Salmonella Enteritidis: Surveillance Data and Policy Implications Alejandro Pérez, MPH Enteric Diseases Epidemiology Branch Division of Foodborne, Bacterial and Mycotic Diseases National Center for Zoonotic, Vector-Borne, and Enteric Diseases Centers for Disease Control and Prevention
Glossary of Terms Salmonella Enteritidis (SE) - the bacteria Salmonella enterica serotype Enteritidis Serotype - strain of Salmonella based on reaction with specific antibodies Salmonellosis - the disease caused by infection by Salmonella enterica Isolate - Salmonella bacterium obtained from a single laboratory culture
Salmonella A genus of gram-negative, rod-shaped bacteria Live in intestines and peri-reproductive tissues (ovaries, milk glands, etc) Few species, but thousands of serotypes
Salmonellosis Disease caused by infection with Salmonella Symptoms include diarrhea, fever, abdominal cramps Starts 12-72 hours after infection and lasts 4-7 days Severe cases can result in hospitalization and can infect the blood and lead to death Infants, the elderly, and immunocompromised are most at risk
Salmonella Enteritidis and eggs Eggs identified as primary vehicle for SE infection Exterior of eggs contaminated by contact with feces Interior of eggs contaminated via transovarian transmission In 1990 s it was estimated that 7% of egg farms had SE and 1 in 20,000 eggs were positive for SE
National Salmonella Surveillance Surveillance for individual patients Salmonellosis is a nationally notifiable disease Surveillance for foodborne outbreaks Two or more people ill due to a common food exposure May be reported to or recognized by health departments
National Salmonella Surveillance Established in 1970s System Collects information on individual patients Public Health Laboratory Information System Electronic reporting of isolate data by public health labs Includes serotype information Passive surveillance
No. Isolates 30000 25000 20000 15000 10000 5000 0 Top four Salmonella serotypes, 1970-2007 70 73 76 79 82 85 88 91 94 97 00 03 06 Year S. Typhimurium S. Enteriditis S. Newport S. Heidelberg
No. Isolates 14000 12000 10000 8000 6000 4000 2000 0 Top four Salmonella serotypes, 1970-2007 70 73 76 79 82 85 88 91 94 97 00 03 06 Year S. Typhimurium S. Enteriditis S. Newport S. Heidelberg
N o. Is o l a t e s 12000 10000 8000 6000 4000 2000 0 SE isolations, 1989-2007 10,201 4,914 5,333 89 91 93 95 97 99 01 03 05 07 Year
12 SE rates by region, 1970-2007 Incidence Rate (per 100,000) 10 8 6 4 2 0 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02 04 06 Year New England Mid Atlantic Pacific Other Mountain
Percent of Salmonella that is Salmonella Enteritidis - 1985 Less than 15% At least 15%, less than 25% CDC 25% or more
Percent of Salmonella that is Salmonella Enteritidis - 1994 CDC Less than 15% At least 15%, less than 25% 25% or more
National Salmonella Surveillance System - Summary Salmonella Enteritidis currently most reported Salmonella serotype Peaked in 1995, but still high with over 5,000 cases in 2007 Spread quickly across the US starting in the northeastern states
FoodNet Active surveillance for foodborne diseases in ten states Participate in conducting active surveillance, surveys, and epidemiologic studies Aim to gain better understanding of epidemiology of foodborne diseases
FoodNet sites 1996-2007 Year 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 Pop (millions) 14.3 16.1 20.7 25.9 30.6 34.9 38.0 41.9 44.5 44.9 45.4 15% of U.S. population 2007 45.9
Relative Rate Relative rates of laboratory-diagnosed Salmonella Enteritidis cases, FoodNet sites, 1996 2008 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 96-98 99 00 01 02 03 04 05 06 07 08 Year
The surveillance pyramid Reported Culture-confirmed case Lab tests for organism Specimen obtained Person seeks care Person becomes ill Population exposed
FoodNet s contribution to the surveillance pyramid Reported Culture-confirmed case Lab tests for organism Specimen obtained Person seeks care Person becomes ill FoodNet: Active surveillance Laboratory survey Physician survey Population survey Population exposed
FoodNet s contribution to the surveillance pyramid Estimate that for every reported case of Salmonella Enteritidis, 37 cases go unreported Estimate that 16% of all Salmonella infections acquired outside the USA
multiplied by 38 Specimen obtained Estimate of SE infections, 2007 Reported 5,333 cases reported Culture-confirmed case Lab tests for organism Person seeks care Person becomes ill General population 202,654 estimated cases
FoodNet - Summary Relative rate of Salmonella Enteritidis infection is on the rise There are 38 times more infections than what is reported through passive surveillance systems Therefore over 200,000 SE cases in 2007 16% of infections are acquired abroad
Foodborne Disease Outbreak Surveillance System State and local health departments investigate and report foodborne outbreaks to CDC Surveillance system started in 1973 and has been web-based since 1998 Approximately 1,300 reports per year Data collected: number of cases, implicated food, pathogen, etc
Foodborne disease outbreak reports 1990-2007 No. Outbreaks 1600 1400 1200 1000 800 600 400 533 531 411 514 690 645 602 806 1403 1339 1317 1320 1249 1094 1328 968 1266 1096 200 0 90 92 94 96 98 00 02 04 06 Year
Outbreaks due to Salmonella Enteritidis, No. Outbreaks 90 80 70 60 50 40 30 20 10 0 1990-2007 90 92 94 96 98 00 02 04 06 Year
Percentage of outbreaks due to Salmonella Enteritidis, 1990-2007 % of All Outbreaks 16 14 12 10 8 6 4 2 0 90 92 94 96 98 00 02 04 06 Year
Determining egg association in SE outbreaks All outbreaks investigated by state/local health departments to determine contaminated food vehicle All foods are considered regardless of etiology When traceback investigations are conclusive, SE of the same subtype is often identified on the farms of origin
Attributing egg association to all cases Uncertainty in attributing proportion of cases in egg-associated outbreaks to: Outbreaks with unknown food vehicle Only ½ of outbreaks have vehicle identified Non-outbreak associated cases Majority of SE cases are not associated with an outbreak
Egg-associated illnesses in SE outbreaks, 1985-2007 Egg status Vehicle of food Egg Total determined known Associated Outbreaks 1,112 523 502 376 Illnesses 35,552 25,555 24,464 18,347 High range estimate: 18,347 / 24,464 = 75% Low range estimate: 18,347 / 35,552 = 52% Mid range estimate: (75% + 52%) / 2 = 64%
Foodborne Disease Outbreak Surveillance System - Summary Number of Salmonella Enteritidis outbreaks decreased early on but has leveled off 75% of SE outbreaks with known vehicle were due to eggs Mid-range estimate for all SE outbreaks due to eggs is 64%
Estimated number of SE cases due to eggs in the United States, 2007 Reported SE cases: 5,333 FoodNet multiplier: 38 Proportion acquired outside US: 16% Proportion due to eggs: 64%
Estimated number of SE cases due to eggs in the United States, 2007 5,333 x 38 = 202,654 total cases of SE 202,654 (0.16 x 202,654) = 170,229 cases of SE acquired in US 170,229 x 0.64 = 108,947 egg-associated cases Round to 109,000 egg-associated cases acquired in the USA in 2007
Egg Quality Assurance Programs (EQAPs) Voluntary measures for minimizing contamination of eggs with Salmonella Enteritidis Follow Hazard Analysis Critical Control Point (HACCP) principles Designed around production, management, and monitoring practices Adopted in various states throughout 1990s
Annualized change in incidence of SE in relation to adoption of EQAPs Annualized change in SE incidence relative to EQAP adoption (%) 40 30 20 10 0-10 -20 Before EQAPs After EQAPs 0-5 -4-3 -2-1 0 1 2 3 4 5 Year, relative to EQAP adoption States with five years of data (n=4) States with two years of data (n=7) States with three years of data (n=6) States with one year of data (n=11)
Conclusions Salmonella Enteritidis estimated to cause more than 200,000 illnesses a year Eggs estimated to cause approximately 64% of these cases (ranging from 75% and 52%) Regulation of egg production has been linked with decreased SE incidence Control programs making progress, but need to be standardized and more widely adopted
Acknowledgements National Surveillance Team FoodNet and Outbreak Surveillance Team Dr Barbara Mahon Dr Chris Braden