October Influenza Testing for the Season. Lauren Anthony, MD, MT(ASCP)SBB Medical Director, Allina Medical Laboratories

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1 October 2010 Lauren Anthony, MD, MT(ASCP)SBB Medical Director, Allina Medical Laboratories Influenza Testing for the Season This Year s Influenza Virus: Sporadic cases of seasonal influenza A (H3N2) were confirmed by the Minnesota Department of Health (MDH) during September and October and all Minnesota cases to date have been caused by the seasonal strain, H3N2. Nationwide, the majority of flu cases this fall have been due to seasonal strains, not H1N1. Influenza Prevalence As of late October, influenza prevalence in Minnesota has been very low (<2.5%). Most of the respiratory viruses circulating have been identified as rhinovirus, adenovirus, coronavirus, and parainfluenza. Vaccine Coverage This year s vaccine provides good coverage of the circulating influenza A and B strains identified to date. The circulating seasonal strain, H3N2/A/ Perth/16/2009, is covered by this years vaccine, but was not in last year s vaccine. This year s vaccine also covers 2009 H1N1 and the currently circulating influenza B strain, B/Brisbane/60/2008. Note: Patients who receive the live nasal influenza vaccine (FluMist) can have positive results for all flu tests (rapid antigen, PCR, culture) for 4 days or more after vaccination. This does not occur with the inactivated injectable flu vaccine. Rapid Influenza Antigen Testing Rapid influenza antigen testing was suspended during the H1N1 outbreak last year due to the inability of available rapid tests to detect this strain. Now that seasonal flu strains dominate, rapid influenza testing has resumed. It is important to understand the limitations of rapid tests when interpreting results.

2 The positive and negative predictive values of rapid flu antigen testing depend upon the prevalence of influenza in the population (See Table 1). This means that: There is a high false positive rate, up to 50%, when flu prevalence is low. Negative rapid flu test results do not exclude influenza. Table 1. The positive and negative predictive values of rapid flu testing depend upon the prevalence of flu in the population. If Flu Prevalence And Specificity Then PPV is False Pos. rate is is is VERY LOW (2.5%) GOOD (98%) POOR (39-56%) HIGH (44-61%) MODERATE (20%) GOOD (98%) GOOD (86-93%) LOW (7-14%) If Flu Prevalence And Sensitivity Then NPV is False Neg. rate is is is MODERATE (20%) HIGH (90%) V. GOOD (97-99%) V. LOW (2-3%) HIGH (40%) HIGH (90%) V. GOOD (93-94%) LOW (6-7%) To learn more about predictive values: MiniModules/Predictive_Values/page01.htm Specimens For Rapid Flu Testing The real-world sensitivity of rapid flu testing is highly dependent on specimen quality. Poor specimen collection is a major cause of rapid flu false negatives. Although influenza infection produces copious amounts of nasal mucus, the actual virus is localized and concentrated in the ciliated columnar epithelium of the posterior nasopharynx, not the squamous lining of the nares or in the mucus discharge. Nasopharyngeal specimens (NP swabs/aspirates/washes) give the best results and are always acceptable. Nasal swabs may be acceptable, depending on the test used, but generally have a lower detection rate, especially in adults. See Table 2. 2

3 Table 2: Rapid flu testing Acceptable Specimens Depend Upon the Laboratory Site and Rapid Flu Test Used Allina Hospitals Directigen Flu A/B Preferred: Nasopharyngeal Minitip Culture swab in Bacti Culturette or viral transport medium. Alternate specimens: Nasopharyngeal aspirate or wash in sterile container. Nasal swabs are not acceptable for this test method. Allina Clinics (AMC, Aspen, Quello) QuickVue Flu A/B Preferred: Nasopharyngeal Minitip Culture swab in Bacti Culturette or viral transport medium. Alternate specimens: Nasopharyngeal aspirate or wash in sterile container. Nasal swabs acceptable if collected using a QuickVue foam swab obtained from the laboratory. Detection rates may be lower with nasal specimens. Non-Allina Sites Contact the specific laboratory for specimen requirements and collection devices. H1N1 Testing No Longer Orderable H1N1 testing is not indicated because the circulating influenza A strains are mostly seasonal H3N2. The Minnesota Department of Health identifies and tracks circulating flu strains through a very robust statewide surveillance system, and will keep laboratories and providers informed of any changes in circulating strains and strategies for testing. What Flu Testing Will Be Performed at MDH? This year, MDH will perform influenza testing and strain identification for surveillance only, and will only accept specimens from one patient group: Hospitalized patients with influenza-like illness (regardless of positive or negative flu test results). MDH will perform influenza testing by PCR on these specimens and determine the strain type (H3N2, H1N1, etc.) for surveillance purposes only, not for clinical care. There is a minimum turnaround time of 1-2 weeks. Which Patients Should Have Specimens Sent to MDH? All hospitalized patients with influenza-like illness (regardless of positive or negative flu test results.) 3

4 Is a Separate Specimen Required? Yes, a separate specimen must be collected for MDH. Acceptable specimens include: Nasopharyngeal swab viral transport medium (VTM) Nasopharyngeal aspirate or nasal wash in sterile container. Nasal swab in VTM (note: Although nasal swabs are acceptable for the highly sensitive PCR test performed at MDH nasal specimens are not optimal for rapid flu antigen testing) What Paperwork is Required? There is a new form this year, posted on the MDH website, to be completed by the provider and submitted with each specimen. Allina Medical Laboratories will forward the specimens and paperwork to MDH. How Long Will it Take to Get Results? This year, MDH is performing flu testing for surveillance only, not patient care. For clinical testing, there are several options available through Allina Medical Laboratories that are summarized in Table 3. Case Reporting to MDH This is different than specimen submission. The following case types need to be reported to MDH: All hospitalized Minnesota residents with laboratory confirmed influenza (including rapid testing). This will be done by Allina Medical Laboratories for positive flu test results. Any suspected influenza death or critical illness. Any unusual case incidence or cluster (including long-term care facilities). What are the Options for Clinical Testing for Patient Care? See Table 3 on page 5 for a summary of available tests and recommendations. 4

5 Table 3. Clinical Testing for Influenza Test Advantages Disadvantages Influenza A/B Antigen LAB6696 (INF) Detects and differentiates influenza A and B. See Table 2 for acceptable specimen types, which are different at the hospitals and clinics. See Table 4 for specimen collection instructions. Same day turnaround Rapid results (at the expense of accuracy). Can be helpful for ambulatory care during flu season. Proper specimen collection is essential. False positives and false negatives. Not accurate enough for patients requiring hospital admission PCR testing is preferred. Similar cost to PCR but much less sensitive or accurate. Influenza A & B by PCR LAB994 ( MSO) Viral nucleic acid detection and differentiation of influenza A & B Specimen: Rayon mini-tip swab or throat swab in viral transport medium. Nasopharyngeal aspirate or wash in sterile container. Similar cost to rapid flu testing but vastly more sensitive and accurate. Most accurate, sensitive, and specific test available. Most clinically effective test for flu detection in patients who need to be admitted to the hospital. Compliance/billing issue Can t be ordered if rapid flu testing is performed* Performed at a reference lab. 1 day turnaround Continued on Page 6 5

6 Continued from page 5 Test Advantages Disadvantages Respiratory Viral Panel by PCR LAB994 (MSO) Nucleic acid detection of influenza A/B and other respiratory viruses. Order as LAB994 Test Description: ViroMed # Specimen: NP Swab in Viral Transport Media or Nasal Wash, Nasal aspirate, BAL or Wash in Sterile Container. 1-2 day turnaround Respiratory Viral Culture LAB4724 (VRP) Specimen: NP Swab in Viral Transport Media or Nasal wash, aspirate or BAL in Sterile Container. 2-5 day turnaround H1N1 Highly sensitive and accurate for diagnosis of influenza as well as other respiratory viral infections when clinically appropriate. Detects: Influenza A Influenza B Parainfluenza 1-3 RSV Adenovirus Metapneumovirus Rhinovirus May be ordered as backup to rapid influenza testing. Detects: Influenza A Influenza B Parainfluenza 1-3 RSV Adenovirus Specific testing not indicated at present, but would be detected by PCR for influenza A. High cost (6-fold higher than rapid flu). Compliance/billing issue Can t be ordered if rapid flu testing is performed* 1-2 day turnaround time Performed at a reference lab. High cost (3-6 fold higher than rapid flu, depends on virus detected.) Performed at a reference lab. Not orderable *Influenza PCR and rapid tests are all considered antigen tests. Ordering more than one antigen test for influenza will result in payer rejections and billing compliance issues. 6

7 What precautions are needed when collecting specimens for flu testing? Droplet precautions during swab/aspirate/wash collection: A regular surgical mask, gown, and gloves should be worn. Airborne precautions during aerosol generating procedures such as bronchoscopy, sputum induction, intubation and extubation, open suctioning of airways: A fit-tested N95 mask or equivalent, gown, and gloves. Why isn t it helpful to perform rapid flu testing on patients who will be admitted to the hospital? Rapid flu testing isn t accurate enough to effectively impact inpatient management and could lead to misdiagnosis. A negative rapid flu test does not exclude influenza; therefore, a patient sick enough to be in the hospital with influenza-like illness and a negative rapid flu test would still receive empirical treatment and isolation precautions for influenza. A false positive rapid flu test could result in inappropriate treatment and delay recognition of the patient s true diagnosis. Even the best rapid flu tests (98% specificity) can have up to a 50% false positive rate, depending on prevalence of flu in the population. Molecular (PCR) testing for influenza A and B with next day turnaround provides more clinically useful results for inpatient management. What testing is recommended for inpatients? Influenza A and B detection by PCR, which has a 1-day turnaround and is performed at a reference laboratory. This is the most sensitive and accurate test available. It will detect all strains of influenza A, including H1N1. Strain typing is performed for at MDH for hospitalized patients with influenza. 7

8 Table 4. Rapid Flu A & B Specimen Collection Instructions: Observe droplet precautions: Wear protective surgical mask, gown, gloves, and protective eyewear when collecting rapid flu specimens. Nasopharyngeal Swab Use a Minitip culture swab and Bacti culturette medium or viral transport medium (VTM). 1. As the mini-tip is removed from the package, bend the wire to the shape of the nasal passage. 2. Maintain sterility of the swab. 3. Tip patient s head back and swab through the nostril into the nasopharynx. 4. Rotate the swab gently and remove. 5. If any resistance is met in the passageways, do not force the swab. Try the other nostril. If the swab cannot be passed through either nostril, it may be bent at a right angle and passed through the mouth to the nasopharynx, taking care to avoid mouth and throat contamination. 6. Place swab in culturette tube or viral transport medium. Nasopharyngeal Washing or Aspirate 1. Obtain a nasopharyngeal washing collection kit. 2. With patient in supine position, tilt head back at 70 angle. 3. Attach sterile syringe to catheter. Insert catheter into nostril and instill 2 or 3 ml normal bacteriostatic saline into one nostril and pharynx. Use the minimum amount of saline possible to avoid over-dilution of antigen in the specimen. 4. Aspirate fluid out of nostril with syringe. 5. Gently suction with syringe while withdrawing catheter. 6. Screw tip onto syringe full of solution to prevent leakage during transport or place into sterile screw top container. Transport immediately. Nasal swab (Allina Clinics only). Nasal swabs generally have a lower detection rate than NP swabs, especially in adults. 1. Obtain a special QuickVue foam nasal collection swab from the clinic laboratory. 2. It is important to obtain as much secretion as possible. 3. Insert the sterile swab into the nostril that presents the most secretion under visual inspection. 4. Using gentle rotation, push the swab until resistance is met at the level of the turbinates (less than one inch into the nostril). 5. Rotate the swab a few times against the nasal wall. For questions, comments, or suggestions about this newsletter or other laboratory issues, please contact Lauren Anthony, MD, Medical Director of Allina Medical Laboratories, (612) or Lauren.Anthony@allina.com 8