Rendi Murphree, PhDCDC Epidemic Intelligence Service Officer

Tennessee Department of Health

Council of State and Territorial Epidemiologists Annual Meeting

June 13, 2011

Characteristics of Foodborne Disease Outbreak Investigations Conducted by

FoodNet Sites, 2003–2008

Office of Surveillance, Epidemiology, and Laboratory Services

Scientific Education and Professional Development Program Office

BACKGROUNDFoodNet Outbreak Investigations

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 et al., Foodborne illness acquired in the United States, Emerg Infect Dis, 2011, Jan 7(1)7-15CDC, Foodborne Outbreak Online Database, http://wwwn.cdc.gov/foodborneoutbreaks Accessed 28 June 2010.

Foodborne Disease OutbreakSurveillance 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 OutbreakSurveillance Systems

CDC Foodborne Disease Outbreak Surveillance System NORS All states

Foodborne Disease Active Surveillance Network FoodNet 10 states

OBJECTIVESFoodNet Outbreak Investigations

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

METHODSFoodNet Outbreak Investigations

Data Source

FoodNet sites 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

Variables

NORS 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

Definitions

Foodborne disease outbreak (FBDO) ≥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

*Olsen, et al., MMWR Surveillance Summary, 2000;49(1):1-62

RESULTSFoodNet Outbreak Investigations

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

FBDO by Year — FoodNet Sites, 2003–2008N = 1,200

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

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

FBDO Seasonality by Confirmed Etiology — FoodNet Sites, 2003–

2008 (n = 715)

FBDO Seasonality by Confirmed Etiology — FoodNet Sites, 2003–

2008 (n = 715)

FBDO Seasonality by Confirmed Etiology — FoodNet Sites, 2003–

2008 (n = 715)

FBDO Seasonality by Confirmed Etiology — FoodNet Sites, 2003–

2008 (n = 715)

0

2

4

6

8

10

12

14

16

Pro

po

rtio

n

Month of First Illness Onset

Bacterial Etiology Viral Etiology Unknown Etiology

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)

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)

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%)

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%)

Stool Key to Confirming an Etiology

FBDO Characteristics by Outbreak Size — FoodNet Sites, 2003–2008

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)

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

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 Odds ratio = 4.9 (3.6–6.7)

Source of Initial FBDO Recognition —

FoodNet Sites, 2003–2008Viral

n = 471Bacterialn = 246

No. (%) No. (%)

Private citizen 363 (87) 80 (33)

Reportable disease surveillance 11 ( 3) 75 (30)

Medical professional report 34 ( 8) 43 (17)

DNA match 0 ( 0) 33 (13)

Syndromic surveillance 0 ( 0) 3 ( 1)

Other 10 ( 2) 12 ( 5)

Source of Initial FBDO Recognition —

FoodNet Sites, 2003–2008Viral

n = 471Bacterialn = 246

No. (%) No. (%)

Private citizen 363 (87) 80 (33)

Reportable disease surveillance 11 ( 3) 75 (30)

Medical professional report 34 ( 8) 43 (17)

DNA match 0 ( 0) 33 (13)

Syndromic surveillance 0 ( 0) 3 ( 1)

Other 10 ( 2) 12 ( 5)

Source of Initial FBDO Recognition —

FoodNet Sites, 2003–2008Viral

n = 471Bacterialn = 246

No. (%) No. (%)

Private citizen 363 (87) 80 (33)

Reportable disease surveillance 11 ( 3) 75 (30)

Medical professional report 34 ( 8) 43 (17)

DNA match 0 ( 0) 33 (13)

Syndromic surveillance 0 ( 0) 3 ( 1)

Other 10 ( 2) 12 ( 5)

n = 370

Receipt of Initial FBDO Recognition—

FoodNet Sites, 2006–2007

Settings of FBDO — FoodNet Sites, 2003–2008

Site of food preparation (n = 1,088) 64% restaurant or deli 7% caterer

11% home

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

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%

n = 1,185

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

n = 655

DISCUSSIONFoodNet Outbreak Investigations

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

Study Limitations

Data quality 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

Conclusions & Recommendations

Public health agencies must improve investigation of foodborne disease outbreaks

Recommendations Systematically review complaints from the public Increase stool specimen collection

o Health departments o Clinicians

Consider new methods for identifying and contacting patients and control subjects

Provide training o Conducting epidemiologic studieso Collecting NORS and FoodNet data

For more information please contact Centers for Disease Control and Prevention1600 Clifton Road NE, Atlanta, GA 30333Telephone, 1-800-CDC-INFO (232-4636)/TTY: 1-888-232-6348E-mail: cdcinfo@cdc.gov Web: www.cdc.gov

The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.

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

Office of Surveillance, Epidemiology, and Laboratory Services

Scientific Education and Professional Development Program Office