Influenza in the Department of the Navy: Seasonal Summary NMCPHC-EDC-TR

Transcription

1 Influenza in the Department of the Navy: Seasonal Summary Reportable and Emerging Infections Division Prepared July 2018

2 1 Contents Executive Summary... 3 Objective... 5 Background... 5 Methods... 7 Overall Burden... 8 Laboratory Data... 9 Pharmacy Data... 9 Comorbid Diagnoses for Inpatient Laboratory and Pharmacy Cases... 9 Clinical Encounters for ILI... 9 MERs for Influenza-Associated Hospitalizations Coinfections Vaccinations DON Results Overall Burden Laboratory Data Overall Active Duty and Recruits Children and Other Age Groups Inpatient Cases Co-occurring Diagnoses among Inpatient Laboratory Cases Geographical Distribution Pharmacy Data Overall Active Duty and Recruits Children and Other Age Groups Inpatient Dispensed Antivirals Co-occurring Diagnoses among Inpatient Antiviral Cases Geographical Distribution Encounter-Based ILI Overall Active Duty

3 MERs for Influenza-Associated Hospitalizations Coinfections Vaccinations Active Duty MTF Vaccine Distribution US Fleet Forces Command DOD Results Laboratory Data Pharmacy Data Discussion Strengths Limitations Conclusion References Appendix A: ILI Diagnosis Codes

4 3 Executive Summary (EDC) at the Navy and Marine Corps Public Health Center (NMCPHC) monitors influenza activity on a weekly basis throughout the influenza season, using Health Level 7 (HL7) formatted Composite Health Care System (CHCS) laboratory and pharmacy records; inpatient admission records; outpatient medical encounter records; and vaccination records. This report summarizes influenza activity among Department of the Navy (DON) beneficiaries during the season. The DON influenza season began earlier than in recent years, had a greater number of cases than any past season since EDC influenza surveillance began in 2008, and was a high severity season, based on the number of inpatient cases. Influenza activity began diverging from baseline trends in November and remained elevated well into April, with activity remaining at or above baseline levels for more than 80% of the season. DON trends mirrored those in the general civilian population of the United States (US); both the DON and the Centers for Disease Control and Prevention (CDC) reported influenza activity that peaked during late January into early February DON influenza activity peaked during Week 5 (28 January 3 February 2018). Summary of Results Total DON influenza cases identified from laboratory, pharmacy, and clinical encounter records (inpatient and outpatient) peaked at Week 5 with 2,959 cases. The percentage of cases identified in two or more data sources was 41.7%, with only 15.8% of cases identified in all three data sources. The highest proportion of cases was identified among pharmacy records. The overall percent positivity among DON laboratory specimens was 21.8%. Influenza A was the dominant influenza type during the season (60.0% of positive specimens). The volume of laboratory-positive cases was at or above baseline for 25 of 30 surveillance weeks. Laboratorypositive cases peaked during Week 5 and remained above baseline through Week 9; dispensed antiviral medications (AVs) remained elevated through Week 8. Oseltamivir was the most frequently prescribed AV. A higher percentage of inpatient laboratory-positive cases and inpatient dispensed AVs occurred when compared to past seasons, indicating a season of high severity; both inpatient laboratory-positive cases and dispensed AVs exceeded expected levels for at least ten consecutive weeks during the peak of the season. Influenza-like illness (ILI) cases among DON beneficiaries diverged from trends for laboratory-positive cases and dispensed AVs, with peaks occurring during Week 1 and Week 6. Active Duty and Recruits The seasonal trend of DON AD influenza cases was mostly consistent with the trend for all DON beneficiaries, with elevated activity from Weeks 2-7. The vaccination rate for AD and reserve Sailors and Marines was 95.9% at Week 17 (22 April 2018). The DON achieved 90% vaccination coverage in Week 52 (24 December 2017), two weeks later than the DOD s goal date. The majority (78.3%) of influenza cases among AD DON service members had a record of vaccination at least 14 days prior to infection (which is considered immune). 3

5 4 Geographic Distribution Among DON medical treatment facilities (MTFs) Navy Medical Center (NMC) San Diego had the highest frequency of laboratory-positive influenza cases during the season. Naval Hospital (NH) Pensacola had the highest frequency of AVs dispensed among DON beneficiaries. NH Camp Pendleton and NH Pensacola had the next highest volumes of laboratory cases, while NMC San Diego and NMC Portsmouth experienced the next highest volumes of dispensed AVs among DON MTFs. Navy MTFs located in California and regions outside of the continental US (OCONUS) experienced elevated influenza activity earlier in the season than MTFs located in the mid-atlantic and Southeast regions of the US, consistent with previous seasons. Conclusion Compared to recent years, the DON influenza season was high in both volume and severity. Robust influenza surveillance in the DON was achieved through the use of multiple data sources. Multiple data sources increased the validity of the findings and provided a comprehensive overview of influenza trends among DON beneficiaries. This information may assist the Navy Bureau of Medicine and Surgery (BUMED) in determining the overall burden of influenza in the DON community and its impact on mission readiness, and may assist in policy planning and preparation for the upcoming seasons. 4

6 5 Objective This report summarizes influenza activity among DON beneficiaries during the influenza season. Background Influenza is a contagious, viral respiratory illness that can lead to mild or moderate illness. Symptoms include, but are not limited to, fever, sore throat, malaise, and headaches. In severe cases, influenza may result in pneumonia, respiratory failure, and death. A CDC report on influenza seasons from 2010 to 2016 estimated the number of seasonal influenza-associated deaths ranging from a low of 12,000 ( ) to a high of 56,000 ( ) in the US. 1 Worldwide, the CDC estimates that as many as 646,000 people may die from influenza each season. 2 The influenza virus is categorized into three types. Type A and Type B routinely spread among humans and cause seasonal infections each year. Type C usually results in less severe symptoms and does not cause seasonal epidemics, and therefore is not included in regular influenza seasonal surveillance. An emergence of new influenza strains can result in pandemics, such as the 2009 H1N1 influenza pandemic, or sporadic outbreaks, such as the 2013 avian influenza A (H7N9) virus outbreak in China. 3, 4 The CDC monitors US influenza activity on a weekly basis from October through mid-may. Though seasons vary, a typical influenza season is characterized by a lower incidence of illness in October and November with peak incidence most frequently occurring in February. 5 In 2017, CDC created seasonal severity definitions based on threshold calculations. The thresholds, created using recent seasonal data, provide a limit that must be reached before the severity of a season changes. If the thresholds are crossed in the seasonal peak, then the season severity can change. Seasonal severity is defined by CDC as low, moderate, high or very high. 6 The CDC tracks influenza season severity by monitoring key indicators such as the percentage of deaths attributed to pneumonia or influenza, rates of influenza-associated hospitalizations, number of pediatric deaths, and the percentage of outpatient visits for ILI. Bacterial co-infections associated with influenza may also be monitored as an indicator of influenza season severity. Especially during influenza pandemics, bacterial co-infections are a leading cause of morbidity and mortality. Further, morbidity and mortality rates are higher among influenza-associated bacterial infection cases compared to bacterial pneumonia without influenza infection. 7 Seasonal influenza vaccinations are the most effective method for reducing the likelihood of an influenza viral infection as well as the spread of infection to others. These vaccines are typically recommended for anyone over six months of age and are important for those at high risk for developing complications from influenza. The vaccines are formulated based on predictions of the viruses that are expected to be most prevalent in the upcoming season. Viral antibodies develop within 14 days, on average, after vaccine administration. 7 The CDC s Advisory Committee on Immunization Practices (ACIP) recommended the use of injectable inactivated and recombinant influenza vaccines during the influenza season. Based on the low effectiveness of the live attenuated influenza vaccine (LAIV4) against influenza Type A (H1N1) in the US during the 5

7 and seasons, ACIP recommended discontinued use of this vaccine for the season. 8 Influenza-specific AV medications may reduce influenza symptoms, shorten the period of illness, or prevent serious complications such as pneumonia. 9 Influenza-specific AVs are most effective when a five-day course of treatment is administered within 48 hours of symptom onset. However, clinical benefits have been observed when treatment is initiated beyond the 48 hour window. AVs may also be administered for post-exposure chemoprophylaxis. Antiviral treatment and chemoprophylaxis are important elements of outbreak control among high-risk populations in institutional settings, such as child care facilities, nursing homes, correctional facilities, and military barracks. Risk of complications, type and duration of contact, local public health recommendations, and clinical judgement must all be considered prior to the implementation of AV treatment for infected individuals. Indiscriminate use of AVs may elevate resistance to these medications or reduce seasonal availability. 10 The CDC released one alert via the CDC Health Advisory Network (HAN) during the season as influenza activity was increasing in the US during Week 52 (27 December 2017). The HAN alert served primarily as a notice to providers about the increase of influenza A (H3N2) activity and the clinical implications of a predominantly influenza A (H3N2) season. The alert included recommendations for clinicians on the use of AVs, including an updated summary of approved AVs available for the season. The summary of approved AVs indicated the expanded use of intravenous peramivir for uncomplicated influenza in persons aged two years and older. The alert also highlighted the importance of beginning AV treatment for high-risk patients, which include children under two, adults over the age of 65, pregnant women, and those with certain medical conditions, or very ill patients as soon as possible after symptom onset. Treatment for these populations can be administered prior to confirmatory laboratory testing, as AV treatment for influenza is most effective if administered during the first 48 hours after symptom onset. 11 The CDC reported that the influenza season was more severe in comparison with recent seasons Nationally, influenza activity began increasing during November and peaked for five consecutive weeks during Weeks 2-6 (13 January February 2018). Influenza A (H3N2) was predominate through Week 8 (18 February February 2018) and for the overall season. Consistent with previous seasons, influenza B increased in prevalence toward the end of the season, and was the predominant virus from Weeks Vaccine effectiveness was estimated at 36% for the season, which was less than the 42% effectiveness estimated for the season. The reduced vaccine effectiveness may be partially attributed to the vaccine being less protective against the predominant influenza type (influenza A (H3N2)) during the current season. Vaccine effectiveness from past seasons has shown the seasonal vaccine to be less protective for influenza A (H3N2) as compared to influenza A (H1N1) and influenza B viruses. Increased influenza-related hospitalizations and deaths were reported for the influenza season, a trend observed in past influenza A (H3N2) predominant seasons. 12 Influenza is a concern for military service members as they are at increased risk of infection due to exposure from crowded living conditions, stressful work environments, and deployments to 6

8 7 endemic regions. 13 Seasonal influenza vaccination is required annually for all AD service members and recruits. For the season, the DOD set a goal of 90% influenza vaccination coverage for service members by 15 December The EDC began DOD and DON influenza surveillance during the season using HL7 formatted laboratory and pharmacy data from CHCS. The EDC has retrospective influenza surveillance data starting with the season. From 2008 to 2010, the EDC was funded by the DOD Global Emerging Infections Surveillance and Response System (GEIS) program to provide information about influenza laboratory testing and influenza-specific AV treatment at facilities within the Military Health System (MHS). At the start of the influenza season, DON influenza surveillance expanded to include a variety of other data sources available to the EDC such as the Comprehensive Ambulatory/Professional Encounter Record (CAPER) and the Standard Inpatient Data Record (SIDR). During the season, data availability was impacted by the testing and deployment of a new electronic health record system, MHS GENESIS. As a result of the transition to MHS GENESIS, data from Naval Hospital (NH) Oak Harbor, NH Bremerton, Army Medical Center (AMC) Madigan, and Fairchild Air Force Base (AFB) were not captured for the season. The EDC publishes a weekly comprehensive DON Situational Report (SITREP) that includes information on influenza medical event reports (MERs), bacterial coinfections among influenza cases, vaccination coverage, influenza-related news, and influenza activity within vulnerable populations including hospitalized patients, AD service members, and recruits. The weekly SITREP is distributed to the military public health community and published to the EDC website. 15 Through timely surveillance of influenza activity, information can be disseminated to the preventive medicine community and clinicians, ensuring ongoing situational awareness of evolving influenza trends throughout the influenza season. During the off-season, analysts at the EDC continue to monitor influenza activity and produce a monthly report. Methods EDC influenza surveillance followed the season and week definitions as specified by the CDC. The influenza season for the Northern Hemisphere typically lasts from the first week in October through the last week of March (Weeks 40 through 13), a total of 26 weeks. To account for the extended period of elevated activity during the season, this report encompasses Week 40 through Week 17 (end of April). Based on CDC business rules, for Morbidity and Mortality Weekly Report (MMWR) weeks, a week is defined as the period from Sunday through Saturday. 16 The EDC developed a standard method for applying week numbers to current and historical data, which allows for easy comparison across seasons. This method adjusts for years with 53 weeks, which occurred most recently during the season. The EDC receives HL7 formatted laboratory results and pharmacy transactions from CHCS via the Defense Health Agency Solutions Delivery Division (DHA-SDD) within approximately two days of record generation. These data extracts contain information for all DOD beneficiaries who either sought care or had test results entered into the record at a fixed MTF. Due to the transition 7

9 8 to MHS GENESIS, four MTFs (NH Oak Harbor, NH Bremerton, AMC Madigan, and Fairchild AFB) were not captured in the CHCS data extracts made available to the EDC for the season. Laboratory and pharmacy records were classified as inpatient or outpatient based on the data source and Medical Expense and Reporting System (MEPRS) code within the record. MEPRS codes were used to distinguish inpatient and emergency department (ED) medical encounter records from outpatient medical encounters. Inpatient cases were used as a measure of severity for both inpatient laboratory-positive hospitalizations and inpatient-dispensed AVs. Records were defined as cases based on a 14 day gap-in-care rule; separate cases occurred in the same patient if more than 14 days had elapsed since the prior occurrence. Historical baselines were used as a comparison for current season trends with respect to laboratorypositive results, influenza AVs, and ILI trends. The EDC calculated baselines using a three-year weighted average to compare weekly results with those from the same week during the past three seasons. Colored bands representing one and two standard deviations above seasonal baseline estimates were also displayed in figures for laboratory-positive cases and dispensed influenza AVs. The standard deviation bands provide a reference comparison of trends in time or volume across seasons. Beginning in the season, surveillance thresholds were also introduced to signal influenza activity that exceeded expected values and were established for the percentage of ILI encounters, the number of inpatient laboratory-positive cases, and the number of inpatientdispensed AV cases. A 14 day gap-in-care rule was used to define cases; separate cases occurred in the same patient if more than 14 days had elapsed since the prior occurrence. The DOD officially transitioned to International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) codes for recording diagnoses on 01 October Estimates that were calculated prior to the transition were based on queries of the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes. Following the transition, data requests from the CAPER and SIDR included queries for both ICD-9-CM and ICD-10-CM codes to account for potential lags in coding practices. Appendix A provides a detailed list of the ICD-9-CM and ICD-10-CM codes used in the analysis; additional information is also provided below. Overall Burden The overall burden of influenza in the DON was estimated by assessing the total number of influenza cases identified from medical encounters (both outpatient encounters and inpatient hospital admission), laboratory records, and pharmacy transactions. The data sources were aggregated, and unique cases were identified by applying the gap-in-care case definition. The aggregate data were also used to assess the relationship among databases for the purpose of developing and monitoring a comprehensive influenza surveillance system. The data were analyzed to determine the extent to which cases overlapped within laboratory, pharmacy, and medical encounter records. While laboratory and pharmacy data serve as a gold standard for 8

10 9 influenza surveillance in the DON, the inclusion of encounter records consistently provides a more comprehensive picture of overall influenza burden. Laboratory Data HL7-formatted microbiology and chemistry data were used to identify laboratory-positive influenza specimens and cases. The laboratory data were limited to relevant clinical specimen sources, including throat and nasal sources. The test type [rapid polymerase chain reaction (PCR), direct fluorescent antibody (DFA), or cultures], and influenza type (A, B, A and B, or nonspecific) were assessed for each specimen. Percent positivity was calculated by dividing the number of influenza-positive specimens by the total number of specimens (positive and not-positive only; inconclusive results were excluded). Positive specimens were classified as cases based on the gapin-care case definition. Pharmacy Data HL7-formatted pharmacy transactions were used to assess the number of dispensed influenza AVs. Three influenza AV medications approved by the Food and Drug Administration (FDA) were recommended for use in the US during the influenza season: oral oseltamivir, inhaled zanamivir, and intravenous peramivir. Amantadine and rimantadine were not recommended for influenza treatment or chemoprophylaxis during the season by CDC 10 and were excluded from influenza surveillance for the season. Pharmacy transactions that were cancelled, had unknown prescription status, or had no dispensed medication were excluded from the final data as these prescriptions were likely not distributed from the MTF pharmacy. Transactions were classified as cases based on the gap-in-care case definition. Comorbid Diagnoses for Inpatient Laboratory and Pharmacy Cases Common co-occurring diagnoses for inpatient laboratory-positive cases and cases with influenza AV prescriptions are of interest due to the possible antagonistic relationship between influenza and other diseases. To obtain diagnosis information on possible comorbidities, inpatient laboratory and pharmacy records were matched to inpatient admissions and ambulatory encounter records. The inpatient analysis included records where either the laboratory collection date or pharmacy transaction date was between the admission and discharge dates. The ambulatory record analysis included encounter data where the encounter date occurred 14 days before or after the laboratory collection date or the pharmacy transaction date. Clinical Classifications Software (CCS) groupings were used to classify ICD-10-CM diagnosis codes into corresponding diagnosis categories. Unique diagnosis categories were counted once per case; cases may have been classified in more than one diagnosis category. Clinical Encounters for ILI CAPER and SIDR data were used to monitor ILI trends using diagnosis codes matching the syndromic case definition established by the DOD Electronic Surveillance System for the Early Notification of Community-based Epidemics (ESSENCE) (Appendix A). The percentage of 9

11 1 0 outpatient medical encounters and inpatient admissions containing at least one ILI diagnosis was calculated to evaluate the number of ILI diagnoses related to healthcare utilization at fixed MTFs. Denominators for ILI percentages were established by aggregating the total number of unique appointment identifiers. Inpatient and outpatient records, including those from ED visits, were evaluated. MERs for Influenza-Associated Hospitalizations The Disease Reporting System-internet (DRSi) is utilized by all military service branches for notification of reportable conditions. The Armed Forces Reportable Event Guidelines (2017) require reporting of influenza-associated hospitalizations. Reportable cases are those where the patient is younger than 65 years of age with a laboratory-positive test and a hospital admission date within 14 days after a positive test or three days or less before the positive test. 17 Laboratorypositive cases and AV prescriptions were matched to DRSi MER influenza cases where the date of onset for the MER was within 14 days of the laboratory case or the date of the dispensed AV. Coinfections Bacterial coinfections were identified by matching laboratory-positive influenza cases to respiratory specimens from microbiology cultures and chemistry tests within 14 days of the influenza specimen collection date. Chemistry data were used only to capture rapid tests for group A Streptococcus. Specimens were classified as upper or lower respiratory infections using an algorithm developed by the Hospital Associated Infections and Patient Safety Division at the EDC. Upper respiratory infections (URIs) were defined as those isolated above the larynx (e.g., pharynx, ear, sinus) and lower respiratory infections (LRIs) included tracheal, sputum, or bronchial specimens. Records with nonspecific or other non-respiratory specimen sources (e.g., blood) were not considered in analysis. Potential coinfections from matched microbiology data were individually reviewed to ensure accurate organism identification. Due to small case numbers, coinfections were grouped by genera for analysis. Antimicrobial resistance could not be analyzed. Vaccinations Vaccine coverage among active duty and reserve service members was assessed weekly to monitor progress toward the DOD instruction requiring 90% coverage by 15 December Vaccination coverage was monitored using weekly data extracted from the Medical Readiness Reporting System (MRRS), which provides an aggregated number of vaccinated AD and reserve service members, total number eligible for vaccination, and total number exempt from vaccination in each component. The percentage of personnel immunized was calculated by dividing the number of personnel vaccinated by the number eligible in each command. Throughout the season, MRRS data were also used to assess vaccination coverage in the Commander, Fleet Forces Command (CFFC) and Commander, Pacific Fleet (CPF). In addition to the overall vaccination coverage rate, AD personnel and recruits with a positive influenza laboratory result were matched to patient-level data within the Immunization Tracking 10

12 1 1 System (ITS) to determine seasonal influenza vaccination status at the time of illness. Service members who received the vaccine at least 14 days before the specimen collection date were considered fully immunized. The type of vaccine administered [live attenuated (LAIV), inactivated (IIV), recombinant (RIV), multiple formulations, or unknown] was also assessed using the common vaccine code (CVX) contained within ITS to validate vaccination status. Service members with vaccination records from 01 August 2017 through 28 April 2018 were included to calculate the proportion of vaccinated AD and reserve personnel. The seasonal influenza vaccine is typically made available during August. However, vaccine distribution may have been disrupted for some commands during the season due to Hurricanes Harvey, Maria, and Irma. Influenza vaccination was monitored for all DON beneficiaries to track the volume of vaccines administered and anticipate potential vaccine demand throughout the influenza season at the MTF level. Ambulatory encounters with a Current Procedural Terminology (CPT) code for an influenza vaccination administered in a Navy MTF from 01 September 2017 through 30 April 2018 were evaluated. Duplicate vaccination procedure records that occurred on the same day were not included in the analysis. If more than one influenza-related CPT code appeared in a single encounter record, the first listed influenza-related code was used for analysis. All encounters for a beneficiary were retained if they occurred on different days. 11

13 1 2 DON Results Overall Burden The total number of influenza cases identified from laboratory, pharmacy, and encounter (inpatient and outpatient) records among DON beneficiaries increased by 133.6% from 9,306 cases for the season to 22,432 cases for the season. Cases were most frequently identified in pharmacy data (14,443; 64.4 %), followed by encounter (13,261; 59.1%) and laboratory (7,629; 34.0%) data. Overall, 9,347 cases (41.7%) aligned with two or more data sources; 3,543 cases (15.8%) aligned with all three data sources. However, 13,085 cases (58.4%) were found in only a single data source (Figure 1). These results indicate that a single-source surveillance system would miss a significant number of potential influenza cases. Figure 1. DON Influenza Cases by Data Source: Proportion of Overlap among Sources and Frequency of Detection by Source, Season (n=22,432) 12

14 1 3 Influenza cases peaked during Week 5 (28 January 2018) at 2,959 cases (Figure 2). By week, the highest proportion of cases occurred in either pharmacy (46.0% to 71.2%) or encounter data (52.9% to 68.0%). The proportion of cases identified in laboratory data accounted for the fewest cases throughout the season (19.4% to 50.2%), generally increasing after Week 47 (19 November 2017) and peaking during Week 5. Figure 2. DON Total Number of Influenza Cases from Laboratory, Pharmacy, and Encounter Data, (n=22,432) 13

15 1 4 Laboratory Data Overall The overall volume of laboratory-positive influenza cases among DON beneficiaries during the season (n=7,629) was greater than in the season (n=3,936). Laboratorypositive cases occurred among 7,596 DON beneficiaries. The total number of laboratory-positive cases increased 92.5% from the previous season. In comparison to recent influenza seasons, the season was typified by an earlier start to the season and a higher volume of cases. Laboratory-positive influenza cases peaked during Week 5 at 866, more than twice the number of cases (n=426) that occurred during the peak week of the previous season (Figure 3). Figure 3. Frequency of Laboratory-Positive Influenza Cases among DON Beneficiaries, Seasons 14

16 1 5 The number of laboratory-positive cases was consistently at or above baseline from Week 40 (1 October 2017) through Week 9 (25 February 2018). Over the course of the season, the volume of laboratory-positive cases exceeded baseline levels for 25 of 30 surveillance weeks (83.3%). The number of laboratory-positive cases was elevated and exceeded baseline levels by more than two standard deviations for ten consecutive weeks (Figure 4). Figure 4. Frequency of Laboratory-Positive Influenza Cases among DON Beneficiaries in Comparison with Seasonal Baseline, Season (n=7,629) 15

17 1 6 Approximately 8,098 (21.8%) unique specimens tested positive for influenza. The majority of positive cases were identified by rapid diagnostic testing (4,914; 60.7%), followed by PCR (2,790; 34.5%) and culture (394; 4.9%). The percentage of positive specimens rose above 10% during Week 48 (26 November 2017) and remained elevated above 10% through Week 14 (1 April 2018). The highest percentage of positive specimens occurred during Week 2 (588; 30.8%). Influenza types identified were unevenly distributed among the specimens: 5,508 (68.0%) influenza A, 2,472 (30.5%) influenza B, 71 (0.9%) influenza A and B, and 47 (0.6%) with an unknown influenza type. Influenza A was the predominant virus from the beginning through the peak of the season. Type A laboratory-positive specimens peaked concurrently with the overall peak of the season during Week 5 (n=633). As the season progressed, influenza B became more prevalent. Beginning in Week 9 and continuing through the end of the season, the proportion of specimens identified as Type B exceeded the proportion identified as Type A (Figure 5). Figure 5. DON Laboratory-Positive Influenza Specimens by Influenza Type, Season 16

18 1 7 Table 1 illustrates the demographic characteristics of the 7,629 laboratory-positive influenza cases identified in the season. The frequency of cases was similar by gender, with 3,882 (50.9%) cases among males and 3,747 (49.1%) cases among females. The highest frequency of laboratory-positive influenza cases occurred among children (3,557; 46.6%), followed by spouses (1,612; 21.1%), AD personnel (1,230; 16.1%), and other sponsors (1,091; 14.3%). Table 1. Demographic Characteristics of Laboratory-Positive Influenza Cases among DON Beneficiaries, Season Frequency (%) Total 7,629 Gender Age Group Beneficiary Category Male 3,882 (50.9%) Female 3,747 (49.1%) 0-4 1,134 (14.9%) ,272 (29.8%) ,309 (30.3%) 45+ 1,914 (25.1%) Active Duty 1,230 (16.1%) Recruit 135 (1.8%) Spouse 1,612 (21.1%) Child 3,557 (46.6%) Other: Sponsor 1,091 (14.3%) Other: Non-Sponsor 4 (0.1%) Data source: Health Level 7 (HL7) formatted CHCS pharmacy database. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July

19 1 8 Active Duty and Recruits The DON had 1,230 AD laboratory-positive influenza cases during the season. A total of 874 cases (71.1%) occurred among Sailors and 356 (28.9%) cases occurred among Marines. Among recruits, 135 laboratory-positive influenza cases were identified; Eighty-four (62.2%) cases occurred among Sailors and 51 (37.8%) cases occurred among Marines. The seasonal trend of DON AD influenza cases was mostly consistent with the trend for all DON beneficiaries, with elevated activity from Weeks 2-7. The overall frequency of AD cases for the season was significantly higher than the frequency of cases from recent seasons. Influenza rates for AD Sailors and Marines diverged significantly from seasonal baselines during the peak of the season. The rate among AD Sailors peaked in Week 5 at 30.1 per 100,000 service members. The rate among AD Marines peaked three weeks earlier during Week 2 at 26.1 per 100,000 service members. The influenza rate among AD Sailors was higher than that of AD Marines for 23 of 30 weeks, similar to previous seasons (Figure 6). Figure 6. Rates of DON Laboratory-Positive Influenza Cases by Service, per 100,000 Active Duty Service Members, Season 18

20 1 9 Children and Other Age Groups The frequency of laboratory-positive cases among children (aged 0-17 years) during the season was higher than the previous five seasons and increased by more than 61% over the season (data no shown). Peak frequencies were observed during Week 5 (n=438), two weeks earlier than the season. The number of laboratory-positive cases among children was elevated and exceeded baseline levels by more than two standard deviations for six consecutive weeks (Figure 7). Figure 7. Frequency of Laboratory-Positive Influenza Cases among Children Age 17 and Under in Comparison with Seasonal Baseline, Season (n=3,406) 19

21 2 0 Influenza rates for all age groups of DON beneficiaries were monitored throughout the season. The average rates in children (aged 0-4 years and 5-17 years) were higher than in other age groups. The peak rates of laboratory-positive influenza cases were similar between the two age groups and both peaked in Week 5; the peak rate among children age 0-4 years was per 100,000 population, and the peak rate for children aged 5-17 years was per 100,000 population. The rates for all age groups peaked in Week 5 (Figure 8). Figure 8. Rates of DON-Laboratory-Positive Influenza Cases among DON Beneficiaries, By Age Group, Season 20

22 2 1 Inpatient Cases The total burden of laboratory-positive inpatient cases among DON beneficiaries during the season was higher than the previous season. Of 7,629 total laboratory-positive influenza cases, there were 172 (2.3%) inpatient cases during the season, representing a 72% increase over the previous season. The frequency of inpatient cases exceeded the surveillance threshold for five of 30 surveillance weeks. During the previous three seasons, the highest number of inpatient cases during any week was 15; the weekly frequency of inpatient cases exceeded this maximum for three consecutive weeks (Weeks 51-2) during the season (Figure 9). Most inpatient cases were Type A (124; 72.1%). More than half of the inpatient cases were above the age of 45 years (119; 69.2%). The highest frequency of inpatient laboratory-positive cases occurred among other sponsors (70; 40.7%), followed by spouses (63; 36.6%) and children (22; 12.8%) (data not shown). Figure 9. Inpatient Laboratory-Positive Influenza Cases, DON Beneficiaries, Season (n=172) 21

23 2 2 Co-occurring Diagnoses among Inpatient Laboratory Cases Laboratory-confirmed inpatient cases (n=172) were matched to inpatient hospital admissions and outpatient encounter data to identify co-occurring diagnoses. The twenty most common diagnoses (in any diagnostic position) among influenza-positive inpatient cases are shown in Table 2 (excluding administrative and unclassified residual codes). An influenza diagnosis was included in the encounter record among 91.9% of the laboratory-confirmed inpatient cases. Essential hypertension was identified in 54.1% of cases and other lower respiratory disease was identified in 47.1% of the cases. Other conditions that may increase the risk of influenza-related complications include uncomplicated diabetes mellitus (31.4%), diabetes mellitus with complications (23.3%), cardiac dysrhythmias (30.2%), and pneumonia (28.5%). 18 The median duration between admission and discharge for patients with an inpatient admission record and a laboratory-confirmed influenza test was 2 days, with a maximum duration of 71 days. Table 2. Twenty Most Common Diagnoses among Inpatient DON Influenza Laboratory Cases, Season (n=172) Diagnostic Category Frequency Percent Influenza % Essential hypertension % Other lower respiratory disease % Disorders of lipid metabolism % Fluid and electrolyte disorders % Diabetes mellitus without complication % Cardiac dysrhythmias % Pneumonia (except that caused by tuberculosis or sexually transmitted disease) % Other gastrointestinal disorders % Deficiency and other anemia % Other nutritional; endocrine; and metabolic disorders % Esophageal disorders % Diabetes mellitus with complications % Hypertension with complications and secondary hypertension % Screening and history of mental health and substance abuse codes % Chronic kidney disease % Bacterial infection; unspecified site % Fever of unknown origin % Coronary atherosclerosis and other heart disease % Thyroid disorders % Includes all diagnoses in any diagnostic position from inpatient and outpatient records within 14 days of the laboratory-identified case. Cases may be classified within more than one diagnostic category. Data source: Standard Inpatient Data Record (SIDR) and Comprehensive Ambulatory/Professional Encounter Record (CAPER) database. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July

24 2 3 Geographical Distribution NMC San Diego had the highest frequency of laboratory-positive influenza cases during the season, followed by NH Camp Pendleton and NH Pensacola. The seven facilities with the highest frequencies of laboratory-positive cases among DON beneficiaries were Navy facilities. Two joint facilities and two non-navy facilities were also in the top 25 for DON cases. Brook Army Medical Center (BAMC-FSH) reported the highest proportion of cases from a non-navy facility and contributed 4.7% (n=356) of all DON laboratory-positive influenza cases for the season (Figure 10). Figure 10. Top 10 Facilities with the Highest Frequency of Laboratory-Positive Influenza Cases among DON Beneficiaries, Season 23

25 2 4 MTFs in the National Capital and Navy Medicine East regions of the US experienced higher burdens of laboratory-positive influenza cases later in the season as compared to MTFs located in Navy Medicine West regional locations. NMC San Diego peaked in Week 51 (17 December 2017), which was six weeks earlier than the overall DON peak in Week 5 (Figure 11). Figure 11. Weekly Frequencies of Laboratory-Positive Influenza Cases at DON MTFs Reporting the Highest Overall Frequencies in the Season Data source: Health Level 7 (HL7) formatted CHCS pharmacy database Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July

26 2 5 Pharmacy Data Overall The total number of influenza AVs dispensed to DON beneficiaries during the season (n=14,443) increased by more than 154% from the season (n=5,678). The weekly frequency of AVs dispensed among DON beneficiaries in the season peaked earlier than in the season, and the season had the greatest number of AVs dispensed overall compared to the past five seasons. The weekly volume of AVs began to increase sharply after Week 49. The frequency of dispensed AVs peaked during Week 5 (n=1,926) and was more than three times the number of AVs dispensed (n=592) during the peak week of the previous season (Figure 12). Figure 12. Frequency of Influenza Antiviral Prescriptions Dispensed to DON Beneficiaries, By Season,

27 2 6 Similar to the seasonal trend for laboratory-positive cases, the number of dispensed AVs was consistently at or above baseline for the majority of the season. The volume of dispensed AVs exceeded baseline levels for 26 of 30 surveillance weeks (86.6%) and exceeded baseline levels by more than two standard deviations for 11 consecutive weeks (Figure 13). Figure 13. Frequency of Influenza Antiviral Prescriptions Dispensed to DON Beneficiaries in Comparison with Seasonal Baseline, Season (n=14,443) 26

28 2 7 Of all AVs dispensed to DON beneficiaries, oseltamivir was most frequently prescribed (99.9%), followed by zanamivir (<0.1%) (Table 3). In 2017, the FDA expanded peramivir use for children ages 2-17, but only two intravenous peramivir transactions were identified among DON beneficiaries during the season (data not shown). Table 3. Antivirals Dispensed, DON Beneficiaries, Season Drug Outpatient (%) Inpatient (%) Total OSELTAMIVIR 13,886 (96.2%) 554 (3.8%) 14,440 ZANAMIVIR 2 (66.6%) 1 (33.3%) 3 Total 13,888 (96.2%) 512 (3.5%) 14,443 Data sources: Health Level 7 (HL7) formatted CHCS chemistry and microbiology databases. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July Table 4 illustrates the demographic characteristics of the DON beneficiaries among which 14,443 total AVs were dispensed. There were equal amounts of dispensed AVs for females (51.2%) and for males (48.8%). Similar to trends in beneficiary categories among laboratory-positive cases, the highest frequency of AV cases occurred among children (5,731; 39.7%), followed by spouses (3,908; 27.1%), other sponsors (2,373; 16.4%), and AD service members (2,305; 16.0%). 27

29 2 8 Table 4. Demographic Characteristics of DON Beneficiaries Dispensed Antiviral Drugs, Season Frequency (%) Total 14,443 Gender Age Group Beneficiary Category Male 7,051 (48.8%) Female 7,392 (51.2%) 0-4 2,028 (14.0%) ,339 (23.1%) ,537 (31.4%) 45+ 4,539 (31.4%) Active Duty 2,305 (16.0%) Recruit 114 (.8%) Spouse 3,908 (27.1%) Child 5,731 (39.7%) Other: Sponsor 2,373 (16.4%) Other: Non-Sponsor 12 (.1%) Data source: Health Level 7 (HL7) formatted CHCS pharmacy database. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July Active Duty and Recruits In the season, 2,305 (16.0% of the DON) AVs were dispensed to AD service members; Sailors received 1,759 (76.3%) of these AVs and Marines received 546 (23.7%). Among recruits, 114 AVs were dispensed; recruit Sailors received 76 (66.7%) of these AVs and recruit Marines received 38 (33.3%). The weekly frequency of dispensed AVs for AD service members followed a trend similar to the overall trend for DON beneficiaries, with the peak (n=279) occurring during Week 5. The overall frequency of AVs dispensed to AD service members for the season was significantly higher than the volume in recent seasons. AV rates for AD Sailors and Marines moved away from seasonal baselines during the peak of the season. The rate among AD Sailors peaked in Week 5 at 66.7 per 100,000 service members. In contrast, the rate among AD Marines peaked one week earlier during Week 4 at 37.5 per 100,000 service members. The influenza rate among AD Sailors was higher than that of AD Marines for 29 of 30 weeks (Figure 14). 28

30 2 9 Figure 14. Rates of Influenza Antiviral Prescriptions Dispensed by Service, per 100,000 Active Duty Service Members, Season 29

31 3 0 Children and Other Age Groups The total number of AV prescriptions dispensed to children (aged 0-17 years) during the season was 5,367 and was significantly higher than in previous seasons. Peak frequencies were observed during Week 5 (n=822). The number of AVs dispensed among children was elevated and exceeded baseline levels by more than two standard deviations for six consecutive weeks (Figure 15). Figure 15. Frequency of Influenza Antiviral Prescriptions Dispensed among Children Age 17 and Under in Comparison with Seasonal Baseline, Season (n=5,367) 30

32 3 1 The rates of dispensed AVs among DON beneficiaries were highest among children. The peak rates were similar between the two age groups (0-4 years and 5-17 years); both peaked during Week 5. The peak rate among children age 0-4 years was per 100,000 population, and the peak rate for children age 5-17 years was per 100,000 population. Consistent with overall trends for the season, the rates for all age groups peaked in Week 5 (Figure 16). Figure 16. Rates of Influenza Antiviral Prescriptions Dispensed among DON Beneficiaries, By Age, Season 31

33 3 2 Inpatient Dispensed Antivirals Among the 14,443 AVs dispensed during the season, 555 transactions (3.9%) occurred in an inpatient setting among 552 beneficiaries. The frequency of inpatient dispensed AVs exceeded the surveillance threshold for 15 of 30 surveillance weeks (Figure 17). For four consecutive weeks, the frequency of inpatient dispensed AVs exceeded the maximum weekly frequency (n=47) observed in any of the previous three seasons. Figure 17. Influenza Antiviral Prescriptions Dispensed in an Inpatient Setting, DON Beneficiaries, Season (n=555) 32

34 3 3 Co-occurring Diagnoses among Inpatient Antiviral Cases Inpatient dispensed AVs (n=552) were matched to inpatient hospital admissions and outpatient encounter data to identify co-occurring diagnoses. The twenty most common diagnoses (in any diagnostic position) among individuals dispensed an influenza AV in an inpatient setting are listed in Table 5 (excluding administrative and unclassified residual codes). An influenza diagnosis occurred among 78.8% of AV cases. Essential hypertension was identified in 48.7% of individuals and other lower respiratory disease was identified in 45.3% of individuals. A diagnosis of pneumonia, which occurred in 34.1% of inpatient AV cases, is a severe influenza complication. Diagnoses for several other medical conditions that increase the risk of developing influenzarelated complications were also identified, including cardiac dysrhythmias (31.3%), diabetes mellitus without complications (27.5%), and diabetes mellitus with complications (20.1%). 16 The median duration between admission and discharge for patients with an inpatient admission record and dispensed AV was 2 days, with a maximum duration of 77 days. Table 5. Twenty Most Common Diagnoses among DON Influenza Antiviral Recipients, Season (n=552) Diagnostic Category Frequency Percent Influenza % Essential hypertension % Other lower respiratory disease % Disorders of lipid metabolism % Fluid and electrolyte disorders % Pneumonia (except that caused by tuberculosis or sexually transmitted disease) % Cardiac dysrhythmias % Diabetes mellitus without complication % Other nutritional; endocrine; and metabolic disorders % Deficiency and other anemia % Esophageal disorders % Fever of unknown origin % Other gastrointestinal disorders % Screening and history of mental health and substance abuse codes % Hypertension with complications and secondary hypertension % Diabetes mellitus with complications % Chronic obstructive pulmonary disease and bronchiectasis % Chronic kidney disease % Acute and unspecified renal failure % Coronary atherosclerosis and other heart disease % Includes all diagnoses in any diagnostic position from inpatient and outpatient records within 14 days of receiving antiviral medication. Cases may be classified within more than one diagnostic category. Data sources: Standard Inpatient Data Record (SIDR) and Comprehensive Ambulatory/Professional Encounter Record (CAPER) databases. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July

35 3 4 Geographical Distribution NH Pensacola reported the highest volume of dispensed AVs to DON beneficiaries during the season, followed by NMC San Diego and NMC Portsmouth. The five facilities that dispensed the largest number of AVs to DON beneficiaries were Navy facilities. Two joint facilities and two Army facilities were also in the top 25 for dispensed AVs among DON beneficiaries. Brook Army Medical Center (BAMC-FSH) contributed 2.5% (n=358) of all influenza DON AV cases during the season (Figure 18). Figure 18. Top 10 Facilities with the Highest Frequency of Influenza Antiviral Prescriptions Dispensed among DON Beneficiaries, Season 34

36 3 5 MTFs located in California and OCONUS experienced elevated influenza activity earlier in the season than MTFs located in the mid-atlantic and Southeast regions of the US. Among Navy Medicine West facilities, NMC San Diego and NH Camp Pendleton both peaked during Week 1, which was four weeks earlier than the overall DON peak for dispensed AVs in Week 5 (Figure 19). Figure 19. Weekly Frequencies of Dispensed Antivirals at DON MTFs Reporting the Highest Overall Frequencies in the Season Data source: Health Level 7 (HL7) formatted CHCS pharmacy. Prepared by the EpiData Center Department, Navy and Marine Corps Public Health Center, July

37 3 6 Encounter-Based ILI Overall During the season, there were 278,409 total ILI medical encounters and ED visits among DON beneficiaries. The percentage of encounters due to ILI followed general historical trends in the early and late parts of the season. However, ILI trends diverged from historic baselines during the peak of the season. The percentage of ED visits due to ILI peaked during Week 1 (29.8%) and Week 6 (25.2%), and were above baseline from Week 49 through Week 7. The overall percentages of inpatient and outpatient medical encounters due to ILI were less than that of ED visits; inpatient ILI peaked at 11.2% during Week 1 and outpatient ILI peaked one week earlier during Week 52 at 7.9% (Figure 20). ILI trends differ from laboratory and pharmacy trends, exhibiting a peak four weeks earlier in the season. Figure 20. Percentage of Medical Encounters due to Influenza-Like Illness (ILI) among DON Beneficiaries in Comparison with Seasonal Baselines, Season 36

38 3 7 Active Duty The percentage of outpatient encounters attributed to ILI among AD DON service members generally followed baseline trends during the season. A peak occurred during Week 1 with 4.8% of outpatient encounters due to ILI; the baseline peak was one week earlier (Week 52) at 4.2% (Figure 21). Outpatient ILI levels exceeded the surveillance threshold for nine consecutive weeks during the peak of influenza activity. Figure 21. Percentage of Outpatient Medical Encounters due to Influenza-Like Illness (ILI) among Active Duty DON Service Members in Comparison with Seasonal Baselines, Season 37

39 3 8 MERs for Influenza-Associated Hospitalizations During the influenza season, 92 cases of influenza-associated hospitalizations for DON beneficiaries were reported to DRSi. Sixty-one percent (n=56) of MERs had both a corresponding pharmacy and laboratory record. Fourteen percent (n=13) matched only to laboratory records, and 5.4% (n=5) matched only to pharmacy records. Eighteen MERs (19.5%) did not match laboratory or pharmacy records. Influenza-associated hospitalizations were most frequently reported during Week 4 (n=24, data not shown). NMC Portsmouth reported the highest number of influenzaassociated hospitalizations (n=30, data not shown). Those aged years accounted for 50% of MERs, followed by those aged 45 and older (26.1%). A majority of reports were for those with a Navy sponsor service (Table 6). Table 6. Demographic Characteristics of DON Beneficiaries with Inpatient Hospitalizations reported to the Disease Reporting System-internet (DRSi), Season Frequency (%) Total 92 Gender Age Group Service Beneficiary Category Source Male 43 (46.7%) Female 49 (53.3%) (13.0%) (10.9%) (50.0%) (26.1%) Navy 74 (80.4%) Marine Corps 18 (19.6%) Sponsor 50 (54.3%) Spouse 18 (19.6%) Child 24 (26.1%) DRSi Only 18 (19.6%) DRSi and Lab 13 (14.1%) DRSi and Pharmacy 5 (5.4%) DRSi and Lab and Pharm 56 (60.9%) Data sources: Health Level 7 (HL7) formatted CHCS pharmacy database, laboratory database and Disease Reporting System-internet. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July

40 3 9 Coinfections During the season, 3.7% (n=285) of laboratory-positive influenza cases had a bacterial respiratory coinfection. Table 7 details the demographic characteristics of laboratory-positive influenza cases with a bacterial coinfection. Upper respiratory bacterial coinfections (URIs) represented 91.5% (n=261) of all coinfections (n=285) and were present in 3.4% of all influenza cases. Among DON beneficiaries with a coinfection (n=285), 52.2% (n=149) were children ages 5-17 years old with a URI. More than 90% (n=260) of these children were seen in outpatient encounters. Lower respiratory bacterial coinfections (LRIs) represented 8.4% (n=24) of all coinfections and were present in 0.3% of all influenza cases. Among DON beneficiaries with a coinfection (n=285), 7.0% (n=20) were adults ages 45 and older with an LRI. Adults ages 45 and older with a LRI represented 1.0% of all laboratory-positive influenza cases. Of the laboratory-positive cases for children aged 5-17, 6.6% (n=150) had a coinfection identified, the largest percentage by age group. Table 7. Demographics of Laboratory-Identified Influenza Cases by Bacterial Coinfection Status and Specimen Type, DON Beneficiaries, Season Gender Age Upper Respiratory (%) Lower Respiratory (%) Total Coinfection (%) Influenza Cases Male 125 (3.2%) 12 (0.3%) 148 (3.5%) 3,882 Female 136 (3.6%) 12 (0.3%) 137 (3.9%) 3, (3.0) 1 (0.1) 35 (3.0) 1, (6.7) 1 (0.0) 150 (6.6) 2, (2.4) 2 (0.1) 57 (2.4) 2, (1.2) 20 (1.0) 43 (1.2) 1,914 Beneficiary Category Active Duty 31 (2.5) 0 (0.0) 31 (2.5) 1,230 Recruit 3 (2.2) 0 (0.0) 3 (2.2) 135 Spouse 28 (1.7) 11 (0.7) 39 (2.4) 1,612 Child 187 (5.3) 2 (0.1) 189 (5.3) 3,557 Other Sponsor 12 (1.1) 11 (1.0) 23 (2.1) 1,091 Other Non-Sponsor 0 (0.0) 0 (0.0) 0 (0.0) 4 Encounter Type Outpatient 260 (3.5) 15 (0.2) 275 (3.7) 7,457 Inpatient 1 (0.6) 9 (5.2) 10 (5.8) 172 Total 261 (3.4) 24 (0.3) 285 (3.7) 7,629 Data sources: Health Level 7 (HL7) formatted CHCS chemistry and microbiology databases. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July

41 4 0 Coinfections among laboratory-positive influenza cases represented 13 unique genera of bacterial isolates. Overall, the most commonly identified genus was Streptococcus (n=263). Nearly 99% of Streptococcus coinfections were isolated from upper respiratory specimens. Among lower respiratory specimens, Staphylococcus was the most commonly isolated genus (Table 8). Table 8. Genera of Coinfections among Laboratory-Identified Influenza Cases, DON Beneficiaries, Season Specimen Type Coinfection Genus Upper Respiratory (%) Lower Respiratory (%) Total (%) Streptococcus 260 (98.5%) 3 (9.1%) 263 Staphylococcus 3 (1.1%) 10 (30.3%) 13 Haemophilus 1 (0.4%) 4 (12.1%) 5 Serratia 0 (0.0) 3 (9.1%) 3 Cornybacterium 0 (0.0) 2 (6.1%) 2 Enterococcus 0 (0.0) 2 (6.1%) 2 Pseudomonas 0 (0.0) 2 (6.1%) 2 Stenotrophomonas 0 (0.0) 2 (6.1%) 2 Enterobacter 0 (0.0) 1 (3.0%) 1 Escherichia 0 (0.0) 1 (3.0%) 1 Klebsiella 0 (0.0) 1 (3.0%) 1 Neisseria 0 (0.0) 1 (3.0%) 4 Pantoea 0 (0.0) 1 (3.0%) 1 Total Data sources: Health Level 7 (HL7) formatted CHCS chemistry and microbiology databases. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July

42 4 1 Vaccinations Active Duty The DOD sets an annual goal to reach 90% influenza immunization of all military personnel by 15 December (Week 50). The DON achieved 90% vaccination coverage in Week 52, two weeks later than the DOD s goal date. Among AD service components, the Marine Corps reached the DOD goal for vaccination coverage in Week 51 and the Navy reached the goal three weeks later during Week 2. Among reserve components, the Navy Reserve reached the goal of 90% vaccination coverage during Week 1 and the percentage of vaccinated Marine Corps Reserve remained slightly below the goal at 89.9% for the remainder of the season. It should be noted that MRRS relies on timely reporting; a lag in reporting by units into MRRS may result in a delay in meeting the goal. The final immunization coverage for AD and reserve components of the DON (at Week 17) is presented in Table 9. Table 9. Influenza Vaccination Coverage, DON Active and Reserve Components, Season Service/Component Total Population Number Vaccinated a Number Exempt Percent Vaccinated b Navy Active Duty 320, ,495 2, % Navy Reserve 50,316 47, % Marine Corps Active Duty 155, , % Marine Corps Reserve 35,153 30, % Total 561, ,554 4, % a Includes injection influenza vaccines only for the season. b Percent vaccinated is calculated as the proportion of service members vaccinated out of total eligible members. Immunization status is current as of 01 May Data source: Medical Readiness Reporting System (MRRS) database. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July

43 4 2 Among the 1,230 AD service members with a laboratory-positive influenza record in the season, 963 (78.3%) were vaccinated more than 14 days prior to their influenza infection, meaning that they were considered to be fully immune to the influenza virus. One AD case was vaccinated with a vaccine of unspecified formulation. Nearly twelve percent (n=144) of laboratory-positive AD cases had no record of vaccination, and a further 123 (10.0%) were vaccinated less than 14 days prior to infection, meaning that they were not yet immune to influenza at the time of infection. A total of 135 recruits had a laboratory-positive influenza report. Fortyfour (32.6%) recruits were vaccinated more than 14 days prior to their infection and 67 (49.6%) were vaccinated less than 14 days prior to infection. Table 13 presents the vaccination status of AD and recruit laboratory-positive influenza cases and the type of vaccination received. Table 10. Vaccination Status of DON Active Duty and Recruit Influenza Cases, Season Status Immunity Status IIV RIV Unspecified Formulation Active Duty Multiple Formulation None Total Percent Vaccinated; immune % Vaccinated; not immune % No vaccination record % Total 1, ,230. Recruit Vaccine Type Vaccinated; immune % Vaccinated; not immune % % Total RIV=recombinant influenza vaccine (injection), IIV=inactive influenza vaccine (injection). Vaccinated, immune: vaccinated more than 14 days prior to infection. Vaccinated, not immune: vaccinated less than 14 days prior to infection, or after infection. Data source: Health Level 7 (HL7) chemistry and microbiology databases. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July

44 4 3 MTF Vaccine Distribution There were a total of 330,069 outpatient encounters for influenza vaccination at Navy MTFs for all DOD beneficiaries between 01 September 2017 and 30 April The most frequently administered types of influenza vaccines were inactivated, injectable, quadrivalent, preservativefree influenza formulations (59.8%), which are categorized by CPT code (Table 11). Only injectable quadrivalent vaccines were administered to DOD beneficiaries this season; intranasal versions of the influenza vaccine were not recommended for use in the season. Table 11. Influenza Vaccines Administered at Navy MTFs by Type, All DOD Beneficiaries, September 201 through April 2018 CPT Code CVX Code Vaccine Type Count Percent Influenza, injectable, preservative free, quadrivalent (cciv4), for persons 4 years and older 49, % Influenza, injectable, quadrivalent, preservative free, for persons 3 years and older 197, % Influenza, injectable, quadrivalent, contains preservative, for persons 6 months and older 82, % Influenza, injectable, quadrivalent (cciv4), for persons 4 years and older % Total 330,069 Data source: Comprehensive Ambulatory/Professional Encounter Record (CAPER) database. Prepared by the EpiData Center, Navy and Marine Corps Public Health Center, July

45 4 4 US Fleet Forces Command US Fleet Forces achieved 90% influenza vaccination during Week 50, which was the DOD goal date for 90% vaccination (15 December 2017). CPF surpassed the DOD s goal by achieving 91.8% vaccination coverage in Week 49. CFFC reached the goal one week later by achieving 90.2% vaccination coverage in Week 50 (Figure 22). At the end of the season (Week 17), 98.0% of eligible Fleet Forces personnel had received an influenza vaccination. Figure 22. Influenza Vaccination Coverage for Commander, Fleet Forces Command (CFFC) and Commander, Pacific Fleet (CPF), Season 44

46 4 5 DOD Results Laboratory Data During the season, 33,216 laboratory-positive influenza cases occurred among DOD beneficiaries, a 99.7% increase over the season. Approximately 22.8% of unique specimens (n=36,774) tested positive for influenza. The majority of positive specimens were identified by rapid diagnostic testing (23,210; 63.1%), followed by PCR (10,285; 28.0%) and culture (3,278; 8.9%). The highest percentage of positive specimens occurred during Week 2 (32.9%) (7 January 2018). The percentage of positive specimens rose above 10% during Week 46 (12 November 2017) and remained elevated above 10% through the remainder of the season. The most common influenza type among laboratory-positive specimens was influenza A (67.2%), followed by influenza B (31.1%), dual infection with A and B (1.0%), and nonspecific types (0.7%). Influenza A was the predominant virus from the beginning through the peak of the season. Type A laboratory-positive specimens peaked during Week 4 (n=3,104), one week earlier than the overall season peak. Influenza B became more prevalent as the season progressed. Beginning in Week 8 and continuing through the end of the season, the proportion of specimens identified as Type B exceeded the proportion identified as Type A (Figure 23). Figure 23. DOD Laboratory-Positive Influenza Tests by Influenza Type, Season 45