Each year in the United States, an estimated 76 million persons contract
foodborne illnesses (1). CDC's Emerging Infections Program Foodborne Diseases
Active Surveillance Network (FoodNet) collects data about nine foodborne diseases in
eight U.S. sites to quantify and monitor foodborne illnesses
(2--5). This report describes preliminary surveillance data for 2000 and compares them with 1996--1999 data.
The data indicate the relative frequency of diagnosed infections, demonstrate
substantial regional variation, and suggest trends in incidence. FoodNet provides data
for monitoring foodborne illnesses and interventions designed to reduce them.
In 1996, active surveillance began for laboratory-confirmed cases
of Campylobacter, Escherichia coli O157,
Listeria monocytogenes, Salmonella, Shigella,
Vibrio, and Yersinia entercolitica infections in Minnesota, Oregon, and
selected counties in California, Connecticut, and Georgia. In 1997, surveillance for
laboratory-confirmed cases of
Cryptosporidium spp. and Cyclospora
cayetanensis infections was added, and 12 Georgia counties and Fairfield County in Connecticut were added to
the surveillance area. In 1998, the surveillance area for Connecticut became
statewide and active surveillance began in selected counties in Maryland and New York. In
1999, the remaining counties in Georgia and eight counties in the metropolitan Albany,
New York, area were added. In 2000, 11 counties in Tennessee and Contra Costa County
in California were added, bringing the FoodNet surveillance population to 29.5
million persons (10.8% of the 1999 U.S. population)
(6). To identify cases, surveillance personnel contact each clinical laboratory in their surveillance area either weekly
or monthly depending on the size of the clinical laboratory. Cases represent the
first isolation of a pathogen from a person by a clinical laboratory; most specimens
were obtained for diagnostic purposes from ill persons.
Preliminary incidence figures for 2000 were calculated using the number of
cases of diagnosed infections that FoodNet had identified at clinical laboratories as
the numerator and 1999 population estimates as the denominator
(6). Final incidence rates will be calculated when 2000 population census counts are available.
The data for 2000 are presented in two ways: from the five original sites and
from the expanded eight site population. The eight site data are likely to represent
better the national picture. During 2000, 12,631 laboratory-confirmed cases of nine
diseases under surveillance were identified: 4640 of campylobacteriosis, 4237 of
salmonellosis, 2324 of shigellosis, 631 of E.
coli O157 infections, 484 of cryptosporidiosis, 131
of yersiniosis, 101 of listeriosis, 61 of
Vibrio infections, and 22 of cyclosporiasis.
Among the 3686 Salmonella isolates serotyped, 862 (23%) were serotype Typhimurium,
565 (15%) were serotype Enteritidis, 399 (11%) were serotype Newport, and 248
(7%) were serotype Heidelberg. Among the 2192
Shigella isolates with a known species, 85% were
S. sonnei and 13% were S.
flexneri. Among the 52 Vibrio isolates
with known species, 35 (67%) were V.
parahaemolyticus, five (10%) were V.
cholerae nontoxigenic, and four (8%) were V.
Overall in 2000, incidence of diagnosed infections per 100,000 population
was highest for Campylobacter, followed by
Salmonella and Shigella (Table 1).
variation in incidence was reported among the sites for many pathogens. The
most frequently isolated pathogens varied by site (Figure 1), with
Campylobacter most common in five sites and
Salmonella most common in three. The incidence
of laboratory-diagnosed campylobacteriosis ranged from 6.6 per 100,000 population
in Tennessee to 38.2 in California. The incidence of diagnosed infection with
Salmonella was less variable, ranging from 8.9 in Oregon to 18.0 in Georgia. Rates for
infections with specific Salmonella serotypes also varied. Infection with
S. Typhimurium ranged from 1.9 in California to 3.7 in Tennessee,
S. Enteritidis from 1.0 in Georgia and Tennessee to 5.1 in Maryland, and
S. Newport from 0.3 in Oregon to 3.5 in
Tennessee. Incidence of shigellosis ranged from 1.1 in New York to 18.8 in Minnesota,
E. coli O157 infections ranged from 0.5 in Maryland to 4.6 in Minnesota, and yersiniosis varied
from 0.2 in Minnesota to 0.9 in California. The incidence of cryptosporidiosis ranged from
0.2 in Maryland to 3.9 in Minnesota. Listeriosis ranged from 0.1 in Minnesota to 0.5
in Connecticut, and diagnosed Vibrio infections ranged from 0 in New York to 0.9
1996--2000 Rate Comparison
The number of sites and the population under surveillance nearly doubled
since FoodNet began in 1996. To provide consistency, only data from the original five
sites were examined to determine temporal trends (Table 1). Comparing 1996 with
2000, the incidence of laboratory-diagnosed campylobacteriosis declined in the original
five sites combined, and in four of the five original sites individually. The magnitude
and pattern of change varied by site; for example, California, Connecticut, and
Minnesota reported an increase in 2000 compared with 1999 (Figure 2). The incidence
of diagnosed salmonellosis declined in all five sites combined and in each of the
five original sites. Comparing 1996 with 2000, the incidence of infection with each of
the two most common serotypes of Salmonella also declined, from 3.9 to 2.7 for
S. Typhimurium and from 2.5 to 1.8 for
S. Enteriditis. The incidence of listeriosis
declined overall and in each of the sites. The incidence of cryptosporidiosis and
cyclosporiasis also declined after surveillance began in 1997. In comparison, the overall incidence
of shigellosis varied substantially from year to year and from site to site; the
incidence increased in all sites combined and in four of the five individual sites. Large
increases occurred in California and Minnesota during 2000. The overall incidence of
E. coli O157 infections increased in the combined five sites and in four of the five
original sites separately. Substantial year-to-year fluctuation occurred in the rates of
E. coli O157 infections in individual sites, and marked variation occurred from site to
site (Figure 2).
Reported by: S Shallow, MT, M Samuel, DrPH, A McNees, MPH, G Rothrock, MPH,
California Emerging Infections Program; D Vugia, MD, Acting State Epidemiologist, California
Dept of Health Svcs. T Fiorentino, MPH, R Marcus, MPH, S Hurd, MPH, School of Medicine,
Yale Univ, New Haven; P Mshar, Q Phan, M Cartter, MD, J Hadler, MD, State
Epidemiologist, Connecticut State Dept of Public Health. M Farley, MD, W Baughman, MSPH, S Segler,
MPH, Emory Univ School of Medicine and the Atlanta VA Medical Center, Atlanta; S
Lance-Parker, DVM, W MacKenzie, MD, K McCombs, MPH, P Blake, MD, State Epidemiologist, Div of
Public Health, Georgia Dept of Human Resources. JG Morris, MD, M Hawkins, MD, Dept
of Epidemiology and Prevention, Univ of Maryland, Baltimore; J Roche, MD, Acting
State Epidemiologist, Maryland Dept of Health and Mental Hygiene. K Smith, DVM, J Besser, MS,
E Swanson, MPH, S Stenzel, MPH, C Medus, MPH, K Moore, Minnesota Dept of Health.
S Zansky, J Hibbs, MD, D Morse, MD, P Smith, MD, State Epidemiologist, New York Dept
of Health. M Cassidy, T McGivern, B Shiferaw, MD, P Cieslak, MD, M Kohn, MD,
Epidemiologist, Oregon Health Dept of Human Svcs. T Jones, MD, A Craig, MD, W
Moore, MD, State Epidemiologist, Tennessee Dept of Health. Office of Public Health and
Science, Food Safety and Inspection Svc, US Dept of Agriculture. Center for Food Safety and
Applied Nutrition, Food and Drug Administration. Foodborne and Diarrheal Diseases Br, Div
of Bacterial and Mycotic Diseases, Parasitic Diseases Epidemiology Br, Div of
Parasitic Diseases, and Office of the Director, National Center for Infectious Diseases, CDC.
In 2000, FoodNet completed the fifth year of active surveillance
for infections caused by pathogens often transmitted through food. In all 5 years
of FoodNet data collection, Campylobacter was the most frequently
diagnosed pathogen, followed by Salmonella,
Shigella, and E. coli O157; however,
substantial regional and year-to-year variation occurred. Differences in calendar year 2000
rates between the expanded and original populations reflect regional differences
in pathogen isolation rates. Despite year-to-year variation and regional fluctuations,
the general magnitude of incidence and the relative order of pathogens have
remained the same, indicating that this expanded system will be useful for measuring
progress toward the 2010 national health objectives for infections with
Campylobacter (12.3 per 100,000), E.
coli O157:H7 (1.0 per 100,000),
Salmonella (6.8 per 100,000), and
Listeria (0.25 per 100,000) (7).
The incidence of listeriosis in 2000 was lower than in previous years;
however, additional data are required to determine whether these rates represent
year-to-year variation or a sustained trend. Although the incidence of
laboratory-diagnosed Salmonella and
Campylobacter declined from 1996 to 2000, the
year-to-year variations make overall trends difficult to measure precisely. A trend in the
incidence of diagnosed E. coli O157 cannot be discerned, although the incidence increased
from 1999 to 2000 in the original five sites. The substantial overall increase in
shigellosis was caused primarily by large increases in Minnesota and California resulting
from outbreaks (8; T. Aragon, San Francisco Department of Public Health,
personal communication, 2001). An estimated 80% of shigellosis is transmitted
by nonfoodborne routes (1).
Determining the cause of a change in incidence of infections is complex
because foodborne pathogens are transmitted by a variety of food and nonfood routes.
For example, although foods of animal origin are the major source of
Salmonella and E. coli O157 infection, transmission through fresh produce and direct contact
with animals has been increasingly recognized. The changes in incidence of
foodborne infections within FoodNet sites occurred in the context of the introduction of
the HACCP (Hazard Analysis Critical Control Point) regulations for meat and poultry
in processing plants, increased attention to egg and fresh produce safety through
good agricultural practices, industry efforts, food safety education, increased regulation
of imported food, and other prevention measures. Data from outbreak investigations
and comparison of FoodNet data with the results of systematic microbiologic sampling
of meat, poultry, and other foods will help evaluate the impact of prevention measures.
The findings in this report are subject to at least three limitations. First,
although FoodNet surveillance encompassed approximately 10% of the U.S. population in
2000, these data are subject to substantial local variation and may not be
representative nationally, particularly in analyses restricted to the five original sites. Second,
FoodNet data are limited to laboratory-confirmed illnesses, and most foodborne illnesses
are neither laboratory-confirmed nor reported to state health departments. For
example, although clinical laboratories in FoodNet sites routinely test stool specimens
Salmonella and Shigella and almost always test for
Campylobacter, only approximately 50% routinely test for
E. coli O157 and fewer test routinely for
other pathogens. Variations in testing for pathogens might account for some variations
in incidence. Third, some laboratory-confirmed illnesses reported to FoodNet can
be acquired through nonfoodborne routes (e.g., contaminated water,
person-to-person contact, and direct animal exposure); therefore, the reported rates do not
represent foodborne sources exclusively. Additional analyses of FoodNet surveillance
data, foodborne outbreak data (9), and surveys of clinical laboratories,
health-care providers, and consumers will facilitate further interpretation of FoodNet data and
help track temporal trends in foodborne illnesses. Further surveillance and comparison
of the expanded geographic base are necessary to determine which changes
represent year-to-year variation and which are definitive trends.
In 2001, selected counties in Colorado and Maryland will be added to the
FoodNet area, bringing the FoodNet surveillance population to approximately 33.1
million persons (12% of the 1999 U.S. population). The 2000 FoodNet final report will
include incidence figures and other information, such as illness severity, and will be
available later in 2001 at the FoodNet World-Wide Web site, http://www.cdc.gov/foodnet
. Because the population within the FoodNet sites has increased since 1999, the
final 2000 rates will be somewhat lower than the preliminary rates. Preliminary
reports from the 2000 decennial census suggest that population increases might have
been greater than estimated by postcensal figures; therefore, the final adjusted rates
might be lower than the preliminary rates by a greater margin than in previous years.
- Mead PS, Slutsker L, Dietz V, et al. Food-related illness and death in the United
States. Emerg Infect Dis 1999;5:607--25.
- CDC. The Foodborne Diseases Active Surveillance Network, 1996. MMWR
- CDC. Incidence of foodborne illnesses---FoodNet, 1997. MMWR
- CDC. Incidence of foodborne illnesses: preliminary data from the Foodborne
Diseases Active Surveillance Network (FoodNet)---United States, 1998. MMWR
- CDC. Preliminary FoodNet data on the incidence of foodborne illnesses---selected
sites, United States, 1999. MMWR 2000;49:201--5.
- Bureau of the Census, Economics and Statistics Administration, US Department
of Commerce. Population estimates. Available at
http://www.census.gov/population/www/estimates/popest.html . Accessed September 2000.
- US Department of Health and Human Services. Healthy people 2010 (conference ed,
2 vols). Washington, DC: US Department of Health and Human Services, 2000.
- CDC. Outbreak of Shigella sonnei infections associated with eating a
nationally distributed dip---California, Oregon, and Washington, January 2000. MMWR
- CDC. Surveillance for foodborne-disease outbreaks---United States, 1993--1997. In:
CDC surveillance summaries (March). MMWR 2000;49(no. SS-1).