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Characteristics of Foodborne Disease Outbreak Investigations Conducted by FoodNet Sites, 2003–2008 Good morning! Today I’ll discuss the results of our.

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Presentation on theme: "Characteristics of Foodborne Disease Outbreak Investigations Conducted by FoodNet Sites, 2003–2008 Good morning! Today I’ll discuss the results of our."— Presentation transcript:

1 Characteristics of Foodborne Disease Outbreak Investigations Conducted by FoodNet Sites, 2003–2008
Good morning! Today I’ll discuss the results of our study to define Characteristics of Foodborne Disease Outbreak Investigations Conducted by FoodNet Sites during 2003 through 2008. Rendi Murphree, PhD CDC Epidemic Intelligence Service Officer Tennessee Department of Health Council of State and Territorial Epidemiologists Annual Meeting June 13, 2011 Office of Surveillance, Epidemiology, and Laboratory Services Scientific Education and Professional Development Program Office

2 FoodNet Outbreak Investigations
BACKGROUND

3 Annual Burden of Foodborne Illness and Outbreaks in the United States
Foodborne illnesses (estimated) 9.4 million illnesses 1,351 deaths 31 major pathogens Foodborne outbreaks (reported) 20,000 illnesses 20 deaths Investigations identify factors contributing to foodborne illness Etiology and food vehicle often unknown Scallan and colleagues recently estimated 9 million foodborne illnesses occur in the United States each year resulting in more than 1,300 deaths. These illnesses are caused by 31 major pathogens; the largest majority by Norovirus and Salmonella. More than a thousand foodborne outbreaks are reported to the CDC each year. These outbreaks are associated with about 20,000 illness and 20 deaths annually. Investigation of foodborne outbreaks are the most efficient method for identifying factors contributing to foodborne illness like etiology, vehicle, and settings of transmission. Though even in outbreak settings these key components are difficult to elucidate. Scallan et al., Foodborne illness acquired in the United States, Emerg Infect Dis, 2011, Jan 7(1)7-15 CDC, Foodborne Outbreak Online Database, Accessed 28 June 2010.

4 Foodborne Disease Outbreak Surveillance Systems
CDC Foodborne Disease Outbreak Surveillance System NORS (National Outbreak Reporting System) All states Outbreak characteristics Foodborne Disease Active Surveillance Network FoodNet 10 states, CDC, FDA and USDA ~45 million people; 15% of the U.S. population Supplemental data on investigation characteristics Foodborne disease outbreak data are reported to the CDC Foodborne Disease Outbreak Surveillance System. The NORS form is used by all states to report data on enteric outbreaks, including those with a common food vehicle. In addition to national surveillance, the Foodborne Diseases Active Surveillance Network or FoodNet is a collaborative project among 10 states, the CDC, FDA, and USDA. The catchment area includes about 45 million people which represents 15% of the US population. FoodNet data are intended to supplement NORS and provide data on investigation characteristics.

5 Foodborne Disease Outbreak Surveillance Systems
CDC Foodborne Disease Outbreak Surveillance System NORS All states Foodborne Disease Active Surveillance Network FoodNet 10 states Don’t let the nomenclature confuse you, as it has me in the past. NORS is the national system with participation by all US states. Enhanced surveillance is conducted by 10 states that participate in FoodNet.

6 FoodNet Outbreak Investigations
OBJECTIVES

7 Study Objectives Summarize data on FoodNet outbreak investigations
Determine factors associated with identifying an etiology and implicating a food vehicle Describe barriers to successful investigations Recommend investigation improvements We sought to summarize data on FoodNet outbreak investigations, determine factors associated with identifying an etiology and implicating a food vehicle, describe barriers to successful investigations, and recommend investigation improvements that might help elucidate key components of foodborne disease outbreaks.

8 FoodNet Outbreak Investigations
METHODS

9 Data Source FoodNet sites 2003–2008 Multi-state outbreaks excluded
CT, GA, MD, MN, OR, TN Counties in CA, CO, NY NM since 2004 2003–2008 Multi-state outbreaks excluded Combined NORS and FoodNet data Data on FBDOs occurring in the 10 FoodNet sites during 2003 through 2008 were analyzed. Outbreaks with multistate exposures were excluded. We combined data available from NORS and FoodNet for all outbreaks included in the analysis.

10 Variables NORS Form FoodNet Outbreak Supplement Form
Information on the outbreak FoodNet Outbreak Supplement Form Information on the outbreak investigation Recognition and reporting Investigation design Specimen testing Barriers impeding the investigation NORS provided standard information on the outbreak…number of illnesses, earliest illness onset date, etc. FoodNet provided data on the investigations themselves…like how the outbreak was recognized, what study designs were used, the type and number of specimens tested, and barriers impeding the investigation.

11 Definitions Foodborne disease outbreak (FBDO) Food vehicle identified
≥2 cases of a similar illness resulting from the ingestion of a common food Food vehicle identified Statistical evidence or laboratory evidence Etiology confirmed CDC criteria Odds ratios adjusted for outbreak size A FBDO was defined as the occurrence of at least 2 cases of a similar illness resulting from the ingestion of a common food. An investigation successfully identied a food vehicle when at least one food was suspected due to statistical evidence from epidemiological investigation or by using laboratory evidence. Outbreak etiology was confirmed using CDC laboratory criteria. All odds ratios were adjusted to account for outbreak size. *Olsen, et al., MMWR Surveillance Summary, 2000;49(1):1-62

12 FoodNet Outbreak Investigations
RESULTS

13 FBDOs — FoodNet Sites, 2003–2008 42 multi-state outbreaks excluded
1,200 outbreaks analyzed Annual mean number = 200 (range 117–253) 18,593 illness caused by 1,111 outbreaks Mean = 17 per outbreak (range 2–273) Marked variability in outbreak frequency and investigation characteristics Data for 1,200 FBDOs occurring in FoodNet sites during 2003–2008 were included in the analysis. A mean of 200 FBDOs were reported annually ranging from 117 to 253 each year. Around 18,500 illnesses were caused by 1,111 outbreaks for which these data were available. On average, 17 illness were associated with each outbreak reported with a wide range of 2 to 273 illness. As you can see here and on the next slides there was marked variability in outbreak frequency and characteristics over time and among states.

14 FBDO by Year — FoodNet Sites, 2003–2008 N = 1,200
The number of FoodNet outbreaks by year are shown here illustrating fluctuations that occurred in the number of outbreaks reported annually.

15 FBDO Characteristics — FoodNet Sites, 2003–2008
All 10 Sites Number reported 1,200 Average annual rate per million 4 Confirmed etiology (%) 50 Food vehicle identified (%) 32 Etiology & food vehicle identified (%) 20 This table contains general characteristics of outbreaks investigated by FoodNet Sites during ,200 outbreaks translates to an average annual rate of 4 per million population. Only 50% of outbreak investigations were successful in confirming an etiology. A smaller proportion identified a food vehicle, and only 20% successfully identified both.

16 FBDO Characteristics — FoodNet Sites, 2003–2008
All 10 Sites Range Number reported 1,200 11–279 Average annual rate per million 4 1–9 Confirmed etiology (%) 50 37–82 Food vehicle identified (%) 32 16–50 Etiology & food vehicle identified (%) 20 7–39 The range of these data further demonstrates the variability of foodborne disease outbreak characteristics among the 10 FoodNet Sites. I wasn’t brave enough to display state names on the low and upper end of these ranges, but catch me during the break if you’d like to know where your state ranks.

17 FBDO Seasonality by Confirmed Etiology — FoodNet Sites, 2003–2008 (n = 715)
A confirmed etiology was reported for 715 outbreaks and they are plotted here to illustrate seasonality by confirmed etiology. Note proportion by month of first illness onset is plotted from June through May. CLICK Outbreaks with a confirmed bacterial etiology are shown as a solid line and most frequently occurred during summer and fall. In contrast, outbreaks with a confirmed viral etiology, shown as a dashed line, most frequently occurred during winter and spring.

18 FBDO Seasonality by Confirmed Etiology — FoodNet Sites, 2003–2008 (n = 715)
Outbreaks with a confirmed bacterial etiology are shown as a solid line and most frequently occurred during summer and fall

19 FBDO Seasonality by Confirmed Etiology — FoodNet Sites, 2003–2008 (n = 715)
In contrast, outbreaks with a confirmed viral etiology, shown as a dashed line, most frequently occurred during winter and spring.

20 FBDO Seasonality by Confirmed Etiology — FoodNet Sites, 2003–2008 (n = 715)
When I add a dotted line to illustrate the seasonality of outbreaks with unknown etiology, you can see it closely mirrors the seasonality of viral outbreaks suggesting that most outbreaks with unidentifed etiology are caused by viruses.

21 Stool Key to Confirming an Etiology
Stool specimens obtained in 89% of 715 outbreaks with a confirmed etiology vs. 48% of 485 without Odds ratio = 9.2 (6.8–12.3) Over the next few slides I’ll support our finding that stool specimens are key to confirming an etiology. Stool specimens were submitted in almost 90% of outbreaks with a confirmed etiology and less than half of those without a confirmed etiology. The strength of this association is demonstrated by the 9.2 odds ratio . CLICK However, the odds of confirming an etiology did not improve with the collection of more than 4 fecal specimens. And finally… the proportion of outbreaks with a confirmed etiology was high regardless of the median number of days from onset of diarrhea or vomiting to collection of stool specimens. 69% of investigations were successful in confirming an etiology even when stool specimens were collected a median of 14 days after onset of diarrhea or vomiting.

22 Stool Key to Confirming an Etiology
Stool obtained in 89% of 715 outbreaks with a confirmed etiology vs. 48% of 485 without Odds ratio = 9.2 (6.8–12.3) Odds of confirming an etiology did not improve with the collection of >4 stool specimens Odds ratio = 7.2 (4.9–10.6) However, the odds of confirming an etiology did not improve with the collection of more than 4 fecal specimens.

23 Stool Key to Confirming an Etiology
Stool obtained in 89% of 715 outbreaks with a confirmed etiology vs. 48% of 485 without Odds ratio = 9.2 (6.8–12.3) Odds of confirming an etiology did not improve with the collection of >4 stool specimens Odds ratio = 7.6 (5.3–10.9) Proportion of outbreaks with a confirmed etiology high, regardless of interval between symptom onset and stool collection Median 0–3 days (70%), 4–7 days (78%), 8–14 days (69%) And finally… the proportion of outbreaks with a confirmed etiology was high regardless of the median number of days from onset of diarrhea or vomiting to collection of stool specimens.

24 Stool Key to Confirming an Etiology
Stool obtained in 89% of 715 outbreaks with a confirmed etiology vs. 48% of 485 without Odds ratio = 9.2 (6.8–12.3) Odds of confirming an etiology did not improve with the collection of >4 stool specimens Odds ratio = 7.6 (5.3–10.9) Proportion of outbreaks with a confirmed etiology high, regardless of interval between symptom onset and stool collection Median 0–3 days (70%), 4–7 days (78%), 8–14 days (69%) In fact, 69% of investigations were successful in confirming an etiology even when stool specimens were collected a median of 8-14 days after onset of diarrhea or vomiting.

25 FBDO Characteristics by Outbreak Size — FoodNet Sites, 2003–2008
In this histogram, I’ve stratified key outbreak characteristics by the number of illnesses caused. In the left grouping, the proportion of outbreaks with a confirmed etiology among those causing 2 to 4 illness is shown as a red bar, the proportion among outbreaks causing 5-9 illness is shown as a green bar, etc. The take home message is this…as the number of illness associated with an outbreak increased, so did the proportion of outbreak investigations successful in confirming an etiology and implicating a food vehicle. This is why we controlled for outbreak size when calculating measures of association.

26 Keys to Implicating a Food Vehicle
Food vehicle implicated in 47% of 671 outbreaks investigated using a case-control or cohort study vs. 14% of 529 using other methods Odds ratio = 4.9 (3.6–6.7) Now I’ll present components of foodborne disease outbreak investigations associated with implicating a food vehicle. A food vehicle was implicated in nearly half of outbreaks investigated using a case-control or cohort study but the success rate dropped to about 1 in 7 or 14% when these methods were not used. CLICK An analytic study was conducted in only 20% of outbreaks causing 2-4 illnesses and less than half of outbreaks causing 5-9 illnesses. This limitation dramatically lessens the chance of implicating a food vehicle responsible transmission during outbreak investigations. Finally, very few outbreak investigation included food specimen testing though this investigative tool was strongly associated with identifying a food vehicle.

27 Keys to Implicating a Food Vehicle
Food vehicle implicated in 47% of 671 outbreaks investigated using a case-control or cohort study vs. 14% of 529 using other methods Odds ratio = 4.9 (3.6–6.7) Analytic study conducted in only 20% of outbreaks causing 2–4 illnesses An analytic study was conducted in only 20% of outbreaks causing 2-4 illnesses and less than half of outbreaks causing 5-9 illnesses. This limitation dramatically lessens the chance of implicating a food vehicle responsible transmission during outbreak investigations.

28 Keys to Implicating a Food Vehicle
Food vehicle implicated in 47% of 671 outbreaks investigated using a case-control or cohort study vs. 14% of 529 using other methods Odds ratio = 4.9 (3.6–6.7) Analytic study conducted in only 20% of outbreaks causing 2–4 illnesses Food specimens collected in 91 (36%) of 253 investigations successful in identifying a food vehicle Finally, very few outbreak investigation included food specimen testing though this investigative tool was strongly associated with identifying a food vehicle.

29 Source of Initial FBDO Recognition — FoodNet Sites, 2003–2008
Viral n = 471 Bacterial n = 246 No. (%) Private citizen 363 (87) 80 (33) Reportable disease surveillance 11 ( 3) 75 (30) Medical professional report 34 ( 8) 43 (17) DNA match ( 0) 33 (13) Syndromic surveillance 3 ( 1) Other 10 ( 2) 12 ( 5) We examined reported data on the source of initial foodborne disease outbreak recognition. CLICK Among 471 confirmed viral outbreaks, the overwhelming majority were reported to public health authorities by private citizens. In contrast, one-third of bacterial outbreaks were first identified in this manner. Bacterial outbreaks were more frequently recognized through routine disease surveillance, medical professional report, and by DNA analyses; mostly likely CDC PulseNet.

30 Source of Initial FBDO Recognition — FoodNet Sites, 2003–2008
Viral n = 471 Bacterial n = 246 No. (%) Private citizen 363 (87) 80 (33) Reportable disease surveillance 11 ( 3) 75 (30) Medical professional report 34 ( 8) 43 (17) DNA match ( 0) 33 (13) Syndromic surveillance 3 ( 1) Other 10 ( 2) 12 ( 5) Among 471 confirmed viral outbreaks, the overwhelming majority were reported by private citizens.

31 Source of Initial FBDO Recognition — FoodNet Sites, 2003–2008
Viral n = 471 Bacterial n = 246 No. (%) Private citizen 363 (87) 80 (33) Reportable disease surveillance 11 ( 3) 75 (30) Medical professional report 34 ( 8) 43 (17) DNA match ( 0) 33 (13) Syndromic surveillance 3 ( 1) Other 10 ( 2) 12 ( 5) In contrast, one-third of bacterial outbreaks were first identified in this manner. Bacterial outbreaks were more frequently recognized through routine disease surveillance, medical professional report, and by DNA analyses; mostly likely CDC PulseNet.

32 Receipt of Initial FBDO Recognition— FoodNet Sites, 2006–2007
We had data regarding the recipient of the initial report for 370 outbreaks investigated during 2006 and % were received by local or state communicable disease staff and the rest were received by environmental health staff emphasizing the need for close communication between these groups. n = 370

33 Settings of FBDO — FoodNet Sites, 2003–2008
Site of food preparation (n = 1,088) 64% restaurant or deli 7% caterer 11% home Among 1,088 outbreaks where contaminated food was prepared in a single location, the most common site was a restaurant or deli. A small proportion of outbreaks were attributed to food prepared by a caterer or at home.

34 Preparation Leading to FBDO — FoodNet Sites, 2008
Timing of contamination (n = 129) 74% at the time of preparation or serving 26% prior to final preparation Contaminated food served (n = 184) 86% single establishment or event To learn more about the settings of foodborne disease outbreaks, FoodNet collected more detailed information beginning Contamination was thought to have occurred at the time of preparation in 74% of 129 outbreaks. In 86% of 184 outbreaks, investigators reported that contaminated food was served in a single establishment or a single event (e.g. one restaurant, wedding, party, conference). To me, these data implicate two possible scenarios…1) a restaurant failed to cook food to a proper kill temperature or 2) ready-to-eat food was contaminated at a restaurant either by cross-contaminated or by an ill food handler.

35 Agencies Involved in FBDO Investigations — FoodNet Sites, 2003–2008
37% local health departments only 47% local and state agencies 5% local, state and federal agencies Local health departments not involved in 12% Data on agencies involved in the investigation were available for almost all outbreaks in our study; 37% were conducted solely by local health departments, 47% were conducted by local health departments with participation by state agencies, 5% involved local, state and federal partners. Local health departments were not involved in 12% of outbreaks investigations. n = 1,185

36 Barriers Affecting FBDO Investigations — FoodNet Sites, 2003–2008
Notification 18% delayed notification of local health departments Cases 26% too few cases 24% lack of cooperation from cases Controls 23% too few controls 10% inability to identify good controls for an analytic study Stool 25% too few stool specimens At least one barrier affecting the success of the investigation was reported in 655 foodborne disease outbreak investigations. The most frequent responses fell into 4 major themes, these are not mutually exclusive. First, delayed notification of local health departments was a barrier in 18% of outbreak investigations. One quarter reported too few cases or lack of cooperation from cases. Too few controls and too few stool specimens were also frequently reported barriers to successful outbreak investigations. n = 655

37 FoodNet Outbreak Investigations
DISCUSSION

38 Overview of Major Findings
FBDOs: Mainly recognized and handled locally Attributed to exposures outside the home Caused by contamination at time of preparation Stool specimens key to confirming an etiology At least 4 Stool collection weeks after symptom onset useful Analytic study best for implicating a food vehicle Cohort or case-control study Food specimen collection rare but helpful in bacterial outbreaks The results of this study remind us that foodborne disease outbreaks are mainly recognized and handled locally; attributed to exposures outside the home and caused by contamination at the time of preparation or serving. This supports the party line that foodborne disease outbreaks can be prevented through safe food preparation and exclusion of ill restaurant employees. Collection of at least 4 stool specimens markedly improved rates of confirming an etiology. And importantly, we showed that stool specimens are helpful even when collected weeks after symptom onset. Conducting an analytic epidemiologic study is important for successfully implicating a food vehicle. But barriers to enrolling cases and controls must be overcome. Though food specimen collection was rare in this sample, it was strongly associated with implicating a food vehicle in bacterial outbreaks.

39 Study Limitations Data quality Results
Incomplete data submitted to CDC Questions changed over time Subjective interpretation No ongoing training for data collectors Some data not reported by staff directly involved in the outbreak investigation Results May not be generalizable to non-FoodNet sites We acknowledge a few limitations of our data and study results. FoodNet data collected and submitted to CDC may have been incomplete or imprecise. Although data collection instruments were developed with workgroup consensus, all questions were not asked in all years during 2003– Some questions are subjective in nature and their interpretation may have changed over time or with staff turnover. There is no formal ongoing training for data collectors. And often, final data are not reported to by staff directly involved in the outbreak investigation. FoodNet sites are funded to conduct active surveillance for foodborne disease, therefore, these findings may not be generalizable to other U.S. populations under surveillance. For example, the proportion of outbreaks with a laboratory confirmed etiology was 15% higher in our study than reported nationally suggesting that barriers to successful investigations are likely even more substantial in other states.

40 Conclusions & Recommendations
Public health agencies must improve investigation of foodborne disease outbreaks Recommendations Systematically review complaints from the public Increase stool specimen collection Health departments Clinicians Consider new methods for identifying and contacting patients and control subjects Provide training Conducting epidemiologic studies Collecting NORS and FoodNet data To continue learning about the epidemiology of foodborne disease, public health agencies must improve their investigation of foodborne disease outbreaks. Based on our findings, we can offer a few recommendations. Because the majority of outbreaks were reported by private citizens and those reports can be made to variety of personnel within the public health system, we think methods to systematically receive and review complaints from the general public are needed to promote more timely detection of foodborne disease outbreaks. Investigators must also increase the number of stool specimens collected during outbreaks of gastroenteritis. This may require extra effort from local health departments and communication with clinicians to get stool specimen from patients with gastrointestinal illness. Finally, we recommend continued training in designing and conducting epidemiologic studies that should include new methods for identifying patients and control subjects. And ongoing training for collecting NORS and FoodNet data is encouraged to promote high quality data collection.

41 Acknowledgements FoodNet Partners 10 states CDC, FDA, USDA
EIS Supervisory Team Timothy F. Jones John R. Dunn William Schaffner W. Randolph Daley Coauthors Katie Garman Quyen Phan Karen Everstine L. Hannah Gould Timothy F. Jones Finally, I’d like to acknowledge FoodNet Partners and my EIS supervisors and thank my coauthors for their contributions and valuable insight. Thank You Office of Surveillance, Epidemiology, and Laboratory Services Scientific Education and Professional Development Program Office


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