Outbreak Investigation:

Transcription

1 Outbreak Investigation: Principles & Practice Panithee Thammawijaya, MD PhD Bureau of Epidemiology

2 A Call for Help On 16 May 2005, Bureau of Epidemiology (BoE) received a notification call from a northern province An official of a district hospital observed that hundreds of jaundice cases had risen since mid of April 2005 Some of them were diagnosed as suspect acute hepatitis A viral infection to be continue

3 Definition of outbreak The occurrence of cases of an illness, specific health-related behaviour, or other health-related events clearly in excess of normal expectancy. (The area and the period in which the cases occur are specified precisely) 3

4 Excess of normal expectancy More than 5-Year median or Average number + 2sd of previous 5 yr or Average number of previous few wks or months 2 cases with epidemiologic linkage in short time 1 case of an emerging or re-emerging disease 4

5 Detection of an outbreak Sources of outbreak news: Surveillance data that are collected and analyzed timely Health care providers or citizens who knows of several cases. Media: Newspaper, TV, Internet, 5

6 An outbreak of leptospirosis 1500 Number of Cases Reported Cases of Leptospirosis by Month, Thailand, J M M J S N J M M J S N J M M J S N J M M J S N J M M J A greater number of cases than normally occur in the same place when compared to the same duration in the past. 6

7 Detect Epidemic using Signal Detection System (1) Source: Bureau of Epidemiology, Ministry of Public Health, Thailand

8 Detect Epidemic using Signal Detection System (2) Source: US Centers for Disease Control and Prevention

9 The media: main source of outbreak-related information 9

10 Cluster of diseases reported by local person

11 11 Type of Outbreak Source Common source Point Intermittent Continuous Propagated source = person-to-person transmission Mixed source

12 Common source outbreak Food People are exposed just once, or continuously or intermittently to a harmful source Period of exposure may be brief or long 12

13 Epidemic curve of point common source outbreak Case (Point source) 1 incubation period Date of onset Point source All cases occur in 1 incubation period Sharp upward More gradual down slope Able to predict exposure period 13

14 Period of Exposure/Incubation Period for a Point Common Source Outbreak The time between the exposure and the peak of the epi curve represents the median incubation period In point common source outbreaks: If incubation period is known, epi curves can help determine the average period of exposure If the timing of the exposure is known, epi curves can be used to estimate the incubation period of the disease

15 How to calculate exposure time Example: typhoid fever --median incubation period is 15 days Minimum 3 days, maximum 60 days No.of cases Median Incubation Period (IP) Exposure time Min. IP (Point source outbreak) Date of onset 15

16 Example of an Epi Curve for a Common Source Outbreak with Intermittent Exposure Intermittent exposure often results in an epi curve with irregular peaks that reflect the timing and the extent of exposure

17 Example of an Epi Curve for a Common Source Outbreak with Continuous Exposure Continuous exposure will often cause cases to rise gradually (and possibly to plateau, rather than to peak)

18 Distribution of suspected Botulism cases by time and date of onset, March (N=180) No.of cases Case detection and outbreak investigation was initiated ate time am /3/06 15/3/06 16/3/06 17/3/06 18/3/06 19/3/06 20/3/06 21/3/06 22/3/06 date/tim e 18

19 Outbreak Pattern of Spread-Propagated Is spread from person to person Can last longer than common source outbreaks May have multiple waves The classic epi curve for a propagated outbreak has progressively taller peaks, an incubation period apart

20 Example of an Epi Curve for a Propagated Outbreak Incubation period

21 Number of SARS cases in Singapore, February-May 2003 Source: World Health Organization,

22 22 Mixed pattern Have features of both common and propagated source outbreak Have a common source outbreak followed by secondary person to person transmission

23 Mixed epidemic pattern Number of typhoid cases by date of onset, Province S, Thailand confirmed probable suspect 1-4/10/09 5-8/10/ /10/ /10/ /10/ /10/ /10/09 29/10-1/11/09 2-5/11/09 6-9/11/ /11/ /11/ /11/ /11/ /11/09 30/11-3/12/09 4-7/12/ /12/ /12/ /12/ /12/ /12/ /12/09 1-4/1/10 5-8/1/ /1/ /1/ /1/ /1/ /1/10 29/1-1/2/10 2-5/2/10 6-9/2/ /2/ /2/ /2/ /2/10 26/2-1/3/10 2-5/3/10 6-9/3/ /3/ /3/ /3/ /3/ /3/10 30/3-2/4/10 3-6/4/ /4/ /4/ /4/ /4/ /4/ /4/10 Oct Nov Dec Jan Feb Mar Apr

24 Usual sequence of events Primary Case 1st case at PCU Refer Samples To Hospital taken Lab result Response begins Opportunity for control Days 13 24

25 6/31 DAY Ideal sequence of events Primary Case Response begins CASES Potential cases prevented

26 Dr. Carlo Urbani ( ) Dr. Urbani was the first World Health Organization "If I can't (WHO) work in officer such to identify situations, the outbreak of this new disease, in an American businessman who had been admitted to a hospital in Hanoi. Because of his early detection of SARS, global surveillance was heightened and many new cases have been pushing identified paper? and isolated before they infected hospital staff. what am I here for? Answering e- mails, going to cocktail parties and

27 Objectives of Outbreak Investigation 1. Verify outbreak and diagnosis 2. Describe magnitude, severity, and distribution 3. Identify source, mode of transmission, and risk factors 4. Provide appropriate prevention and control measures

28 Steps of an outbreak investigation Establish the existence of an outbreak Verify the diagnosis Prepare for field work Construct a working case definition Find case systematically & record information Perform descriptive epidemiology Develop hypothesis Analytical studies to test hypotheses Special studies (e.g. environmental study, laboratory study) Implementation of control measures and follow-up Communication - - including outbreak report

29 Steps of an outbreak investigation Establish the existence of an outbreak Verify the diagnosis Prepare for field work Construct a working case definition Find case systematically & record information Perform descriptive epidemiology Develop hypothesis Analytical studies to test hypotheses Special studies (e.g. environmental study, laboratory study) Implementation of control measures and follow-up Communication -- including outbreak report Verification & preparation June course 2013

30 Scenario A hundreds of patient visited three adjacent district hospitals with jaundice for the last couple months Is this an outbreak? What is the likely diagnosis? Should we start the investigation? Outbreak confirmed DDx Hepatitis A, B, C? Not confirmed yet Investigation warranted Always ask yourself: What can be done NOW to intervene/control the outbreak? Start general/empirical control measures ASAP!! 30

31 Prepare for Field Work: Rapid Response Team A. Administration and authorization: inform the concerned B. Brief and mobilize multi-disciplinary team: Define tasks and person who be in-charge C. Consultation: clinician, lab, stakeholders, etc. D. Documentation for knowledge: literature, questionnaires, and preliminary information E. Equipment, material, medical and non-medical supplies, e.g. specimen collection & transport

32 Steps of an outbreak investigation Prepare for field work Establish the existence of an outbreak Verify the diagnosis Construct a working case definition Find case systematically & record information Perform descriptive epidemiology Develop hypothesis Analytical studies to test hypotheses Special studies (e.g. environmental study, laboratory study) Implementation of control measures and follow-up Communication - - including outbreak report Describe the outbreak

33 Case definition Components Time Place Person Clinical: signs & Symptoms Laboratory Sources Textbook Literature Expert Interviewing few cases Case definition should not include exposure history (except some diseases with already known exposurse)

34 Multiple case definition Suspected Patient with symptoms.. Probable Suspect case with laboratory (serology) Confirmed Suspect case with laboratory confirmation e.g., culture positive scenario Suspected - Patient who presented three hospitals with jaundice without any underlying medical conditions that can manifest jaundice sign from 1 January 2005 to 17 May 2005 Confirmed - Suspect case who had serum positive for anti HAV IgM 34

35 Active case finding Identify & count cases Perform in clear defined population Attended the party Visited a festival Live in a village Work at a factory Hospitals, laboratories etc. survey Record review Why do active case finding

36 Descriptive data collection and analysis Obtain information Identifying information Demographic information Clinical details Time Risk factors Place Person

37 Identifying info. Investigation form of hepatitis A cases, Northern Thailand, 2005 Date of interview Interviewer's name Patient number Patient's name Age (in years) Gender Address 1. District A 2. District B 3. District C 4. Others. Occupation 1. Farmer 2. Employee 3. Student Demographic 4. Others. info. Clinical symptoms (Jan-May 2005) Possible risk factors No Yes Onset of symptoms Drinking water Y N Jaundice Ice from FactoryW Y N Nausia/Vomiting Fatigue Food A Y N This hepatitis cases is laboratory confiry N Clinical & Lab info. Exposure/Potential Risk Factor 37

38 Identify & count cases Obtain information Analysis of descriptive data Orienting cases in - time - place - person

39 Distribution by Time: Epidemic curve Number of Hepatitis A cases by date of onset, NUMBER total of 3 affected districts, 1 Jan May 05 N=634 Average incubation period INVESTIGATION Source: Panithee Thammawijaya DATE OF ONSET 39

40 Distribution by Place: Map of Number of Case Distribution of Hepatitis A morbidity by district Chaing Rai Chaing Mai Pa yao Lam pang 40 Source: Panithee Thammawijaya

41 Distribution by Person: Specific Attack Rate Hepatitis A Attack Rate by Age Group, total of 3 affected districts, 1 Jan May 05 Attack rate (per 100,000 pop) Source: Panithee Thammawijaya Age group 41

42 Map of Wangnua district: Distribition of HAV cases and Ice, 1 Jan May 05 Source: Panithee Thammawijaya = 5 HAV cases = Wiangpapao Ice = Wangnua Ice Attack rate of Subdistrict that have Wiangpapao Ice = 528 Subdistrict that not have Wiangpapao Ice = 82 (Or 6.4 times!!) 42

43 Steps of an outbreak investigation Prepare for field work Establish the existence of an outbreak Verify the diagnosis Construct a working case definition Find case systematically & record information Perform descriptive epidemiology Develop hypothesis Hypothesis & Analytical studies to test hypotheses Testing Special studies (e.g. environmental study, laboratory study) Implementation of control measures and follow-up Communication -- including outbreak report

44 Cases Person Place Time Evaluate information Pathogen? Source? Transmission? Develop hypotheses from gathered information 32 44

45 Analytic Study Result: Case-control study in Hepatitis A Outbreak Total recruitment > Exclude 73 (previous immuned) Case 70: Control 98 Risk factors Adjusted OR* 95%CI Ice (Any) Ice from Wiangpapao Ka Nom Jeen Party Restaurant Bottle water Tap water Source: Panithee Thammawijaya *Multiple logistic regression controlling for age and village of subjects 45

46 Special studies, e.g., environmental and laboratory studies scenario: Contaminated ice from Wiang Pa pao was the most suspected source of the outbreak. TOILET ICE PRODUCTION AREA WASHING WATER WELL WATER RESERVOIR ARTESIAN WELL COOLING WATER Source: Panithee Thammawijaya OFFICE 46 46

47 Pitfalls in the production process of the ice factory Field testing: Was the well water fecal contaminated? Was chlorination adequate?

48 Result: Laboratory result of environment Source Specimen Result Wiangpapao Ice factory (10 June 2005) Wiangpapao Ice factory (10 June 2005) A patient s house (10 June 2005) Wiangkalong drinking water factory(10 June 2005) Wangnua drinking water factory (10 June 2005) Juice (10 June 2005) Water from well Water from reservoir Water from well Drinking water Drinking water Juice Positive for HAV-RNA (RT-PCR) Positive for HAV-RNA (RT-PCR) Positive for HAV-RNA (RT-PCR) Negative for HAV-RNA (RT-PCR) Negative for HAV-RNA (RT-PCR) Negative for HAV-RNA (RT-PCR) Source: Panithee Thammawijaya 48

49 Steps of an outbreak investigation Prepare for field work Establish the existence of an outbreak Verify the diagnosis Construct a working case definition Find case systematically & record information Perform descriptive epidemiology Develop hypothesis Analytical studies to test hypotheses Response Special studies (e.g. environmental study, laboratory & Action study) Implementation of control measures and follow-up Communication -- including outbreak report

50 Recommend and implement and follow-up the control measures Propagated Source ควบค มร งโรค ต ดทาง แพร กระจาย ป องก นกล ม เส ยง Common Source Source: Principles of Epidemiology, 2nd Edition, Center for Disease Control and Prevention

51 Number of Hepatitis A cases by date of onset, total of WP district, 1 Jan -12 Nov 2005 Number of cases Identify source N=871 ICE FACTORY CLOSING Increase ice demand in Songkran festival Follow up control measure DATE OF ONSET Source: Panithee Thammawijaya

52 After the end of the outbreak Communicate public health message to public Advocate policy makers Evaluate the performance Hot wash, After Action Review Writing report for scientific development 52

53 Outbreak Investigation...in Reality. time Verification Site visit Case definition Organize Data Recommendations Report Publication Outbreak suspected Confirm Diagnosis Form Outbreak Investigation and Control Team Line list Descripitve Epidemiology Control measures Hypothesis & Testing

54 The epidemiologic method is the only way to ask some questions in medicine, one way of asking others, and no way at all to ask many Jerry Morris,

55 THANK YOU