FoodNet Sites Research Articles

Clinical Laboratory Practices for the Isolation and Identification of Campylobacter in Foodborne Diseases Active Surveillance Network (FoodNet) Sites: Baseline Information for Understanding Changes in Surveillance Data

Campylobacter is a leading cause of foodborne illness in the United States. Understanding laboratory practices is essential to interpreting incidence and trends in reported campylobacteriosis over time and provides a baseline for evaluating the increasing use of culture-independent diagnostic methods for Campylobacter infection. The Foodborne Diseases Active Surveillance Network (FoodNet) conducts surveillance for laboratory-confirmed Campylobacter infections. In 2005, FoodNet conducted a survey of clinical laboratories to describe routine practices used for isolation and identification of Campylobacter. A profile was assigned to laboratories based on complete responses to key survey questions that could impact the recovery and isolation of Campylobacter from stool specimens. Of 411 laboratories testing on-site for Campylobacter, 97% used only culture methods. Among those responding to the individual questions, nearly all used transport medium (97%) and incubated at 42°C (94%); however, most deviated from existing guidelines in other areas: 68% held specimens in transport medium at room temperature before plating, 51% used Campy blood agar plate medium, 52% read plates at <72 hours of incubation, and 14% batched plates before placing them in a microaerobic environment. In all, there were 106 testing algorithms among 214 laboratories with a complete profile; only 16 laboratories were fully adherent to existing guidelines. Although most laboratories used culture-based methods, procedures differed widely and most did not adhere to existing guidelines, likely resulting in underdiagnosis. Given the availability of new culture-independent testing methods, these data highlight a clear need to develop best practice recommendations for Campylobacter infection diagnostic testing.

Relative Risk of Listeriosis in Foodborne Diseases Active Surveillance Network (FoodNet) Sites According to Age, Pregnancy, and Ethnicity

Quantitative estimates of the relative risk (RR) of listeriosis among higher-risk populations and a nuanced understanding of the age-specific risks are crucial for risk assessments, targeted interventions, and policy decisions. The RR of invasive listeriosis was evaluated by age, pregnancy status, and ethnicity using 2004-2009 data from the Foodborne Diseases Active Surveillance Network (FoodNet). Nonparametric logistic regression was used to characterize changes in risk with age and ethnicity. Adjusted RRs and 95% confidence intervals (CIs) were evaluated using negative binomial generalized linear models. Among non-pregnancy-associated cases, listeriosis incidence rates increased gradually with age (45-59 years: RR, 4.7; 95% CI, 3.3-6.8; >85 years: RR, 53.8; 95% CI, 37.3-78.9; reference: 15-44 years). The RR was significantly higher for Hispanics than for non-Hispanics (RR, 1.8; 95% CI, 1.3-2.5). Among women of reproductive age (15-44 years), pregnant women had a markedly higher listeriosis risk (RR, 114.6; 95% CI, 68.9-205.1) than nonpregnant women. The RR was higher for Hispanic than non-Hispanic women, regardless of pregnancy status, and this increased during the study period (2004-2006: RR, 1.9; 95% CI, 1.0-3.3; 2007-2009: RR, 4.8; 95% CI, 3.1-7.1). This study quantifies the increases in risk of listeriosis among older persons, pregnant women, and Hispanics in the United States. Additional research is needed to better describe the independent effects of age on risk while accounting for underlying conditions. These estimates are needed both to optimize risk assessment models and to inform targeted interventions and policy decisions.

Characteristics of Foodborne Disease Outbreak Investigations Conducted by Foodborne Diseases Active Surveillance Network (FoodNet) Sites, 2003–2008

A mean of ≥ 1000 foodborne disease outbreaks (FBDOs) causing ≥ 20,000 illnesses are reported to the Centers for Disease Control and Prevention (CDC) annually. We evaluated characteristics of successful outbreak investigations (ie, those that identified an etiologic agent or food vehicle) in the Foodborne Diseases Active Surveillance Network (FoodNet). FBDOs were defined as the occurrence of ≥ 2 cases of a similar illness resulting from ingestion of a common food. FBDOs reported to CDC Foodborne Disease Outbreak Surveillance System during 2003-2008 with FoodNet supplemental data available were included in the analyses. Data regarding 1200 FBDOs were available. An etiologic agent was confirmed in 715 (60%); a food vehicle was identified in 387 (32%). At least 4 fecal specimens were collected in 425 of 639 outbreaks (67%) with a confirmed etiologic agent and 48 of 232 (21%) without a confirmed etiologic agent (odds ratio [OR], 7.6; 95% confidence interval [CI], 5.3-10.9). A food vehicle was identified in 314 (47%) of 671 outbreaks investigated using a case-control or cohort study, compared with only 73 (14%) of 529 outbreaks investigated by using other methods (OR, 5.5; 95% CI, 4.1-7.3). At least 1 barrier affecting the success of the investigation was reported for 655 outbreaks, including too few patients (n = 172; 26%), too few stool specimens (n = 167; 25%), and too few control subjects (n = 152; 23%). Etiologic agent and vehicle are frequently undetermined in FBDOs. Greater emphasis on fecal specimen collection and overcoming barriers to pursuing analytic epidemiologic studies can improve ascertainment of these factors.

Ground beef consumption patterns in the United States, FoodNet, 2006 through 2007.

Infection resulting from foodborne pathogens, including Escherichia coli O157:H7, is often associated with consumption of raw or undercooked ground beef. However, little is known about the frequency of ground beef consumption in the general population. The objective of this study was to describe patterns of self-reported ground beef and pink ground beef consumption using data from the 2006 through 2007 FoodNet Population Survey. From 1 July 2006 until 30 June 2007, residents of 10 FoodNet sites were contacted by telephone and asked about foods consumed within the previous week. The survey included questions regarding consumption of ground beef patties both inside and outside the home, the consumption of pink ground beef patties and other types of ground beef inside the home, and consumption of ground beef outside the home. Of 8,543 survey respondents, 75.3% reported consuming some type of ground beef in the home. Of respondents who ate ground beef patties in the home, 18.0% reported consuming pink ground beef. Consumption of ground beef was reported most frequently among men, persons with incomes from $40,000 to $75,000 per year, and persons with a high school or college education. Ground beef consumption was least often reported in adults ≥65 years of age. Men and persons with a graduate level education most commonly reported eating pink ground beef in the home. Reported consumption of ground beef and pink ground beef did not differ by season. Ground beef is a frequently consumed food item in the United States, and rates of consumption of pink ground beef have changed little since previous studies. The high rate of consumption of beef that has not been cooked sufficiently to kill pathogens makes pasteurization of ground beef an important consideration, especially for those individuals at high risk of complications from foodborne illnesses such as hemolytic uremic syndrome.

Laboratory Practices for the Identification of Shiga Toxin–ProducingEscherichia coliin the United States, FoodNet Sites, 2007

Clinical laboratory practices affect patient care and disease surveillance. It is recommended that laboratories routinely use both culture for Escherichia coli O157 and a method that detects Shiga toxins (Stx) to identify all Stx-producing E. coli (STEC) and that labs send broths or isolates to a public health laboratory. In 2007, we surveyed laboratories serving Foodborne Diseases Active Surveillance Network sites that performed on-site enteric disease diagnostic testing to determine their culture and nonculture-based testing practices for STEC identification. Our goals were to measure changes over time in laboratory practices and to compare reported practices with published recommendations. Overall, 89% of laboratories used only culture-based methods, 7% used only Stx enzyme immunoassay (EIA), and 4% used both Stx EIA and culture-based methods. Only 2% of laboratories reported simultaneous culture for O157 STEC and use of Stx EIA. The proportion that ever used Stx EIA increased from 6% in 2003 to 11% in 2007. The proportion that routinely tested all specimens with at least one method was 66% in 2003 versus 71% in 2007. Reference laboratories were less likely than others to test all specimens routinely by one or more of these methods (48% vs. 73%, p=0.03). As of 2007, most laboratories complied with recommendations for O157 STEC testing by culture but not with recommendations for detection of non-O157 STEC. The proportion of laboratories that culture stools for O157 STEC has changed little since 2003, whereas testing for Stx has increased.

Methods for Monitoring Trends in the Incidence of Foodborne Diseases: Foodborne Diseases Active Surveillance Network 1996–2008

Foodborne illnesses are a substantial health burden in the United States. The Foodborne Diseases Active Surveillance Network (FoodNet) is the principal foodborne disease component of the Centers for Disease Control and Prevention's Emerging Infections Program. FoodNet is a collaborative project among Centers for Disease Control and Prevention, Emerging Infections Program sites, the U.S. Department of Agriculture, and the U.S. Food and Drug Administration. One of FoodNet's main objectives is to monitor changes in the incidence of selected foodborne pathogens. In 1996, FoodNet began active, population-based surveillance for laboratory-diagnosed cases of Campylobacter, Listeria, Salmonella, Shiga toxin-producing E. coli O157, Shigella, Vibrio, and Yersinia infection. Surveillance for cases of Cryptosporidium and Cyclospora infection was added in 1997 and surveillance for non-O157 Shiga toxin-producing E. coli was added in 2000. From 1997 to 2008, the FoodNet surveillance population increased, primarily through the addition of new sites. The increase in the number of FoodNet sites and the size of the population under surveillance as well as the variation in the incidence of infections among sites posed challenges in the selection of the most appropriate method to monitor changes in incidence. To account for variation introduced by changes in population size, a main-effects, log-linear Poisson (negative binomial) regression model was adopted to estimate the magnitude of changes in the incidence of pathogens by comparing current year incidence to reference periods. The article explains how FoodNet uses the negative binomial model to examine changes in incidence over time, describes the reference periods used, explains the graphics used to display results, and discusses future directions in the analysis of trends over time.

Yersinia pseudotuberculosisandY. enterocoliticaInfections, FoodNet, 1996–2007

<i>Yersinia pseudotuberculosis</i>and<i>Y. enterocolitica</i>Infections, FoodNet, 1996–2007

Acute Bloody Diarrhea: A Medical Emergency for Patients of All Ages

Acute bloody diarrhea should be considered a medical emergency. Its causes are frequently serious or actionable or both and are usually identified. However, acute bloody diarrhea as a stand-alone clinical presentation has received little scholarly attention in the past several decades. Although the range of possible causes of acute bloody diarrhea is broad, infectious considerations are paramount and should always be prioritized in the evaluation of such patients. History, examination, and laboratory testing should be focused on minimizing time to diagnosis (and, by extension, to implementing appropriate therapy). Strategically chosen tests and imaging, avoidance of extraneous diagnostic pursuits, and provision of supportive care while awaiting diagnostic clarity are central to the adroit management of patients with acute bloody diarrhea. Diagnostic considerations differ somewhat between adults and children but have many elements in common, including the need for vigilance in detecting Escherichia coli O157:H7 infection. In this review, we discuss diagnostic approaches (emphasizing the importance of rapid, accurate, and thorough microbiologic investigation) and measures that can be taken to support patients while awaiting information that determines the cause of their disease. These topics are discussed in the context of the medical care that is available to children and adults with bloody diarrhea in most institutions in developed nations.

Continued Decline in the Incidence ofCampylobacterInfections, FoodNet 1996–2006

Campylobacter is a leading cause of foodborne illness worldwide. In the United States, changes in the incidence of culture-confirmed Campylobacter infections have been monitored by the Foodborne Diseases Active Surveillance Network (FoodNet) since 1996. In 2006, the incidence of culture-confirmed Campylobacter infection in the FoodNet sites was 12.7 per 100,000 persons. This represents a 30% decline (95% confidence = 35% to 24% decrease) compared to the 1996-1998 illness baseline; however, most of the decline occurred between 1996 and 1999 and the incidence still remains above the national health objective. Important declines were observed in four FoodNet sites (California, Connecticut, Georgia, and Maryland), all age groups, and both sexes. To promote continued progress towards achieving the national health objective, the epidemiology of Campylobacter infections in the United States, including geographic variation and higher incidence among the very young, warrants further study.

FoodNet Survey of Food Use and Practices in Long-Term Care Facilities

Foodborne illness is an important problem among the elderly. One risk factor for foodborne illness and diarrhea-associated mortality among the elderly is residence in a long-term care facility (LTCF); thus, these facilities must implement measures to ensure safe food. To assess safe food practices, knowledge, and policies, we used a mailed, self-administered questionnaire to survey food service directors at LTCFs that were certified to receive Medicare or Medicaid at eight Foodborne Diseases Active Surveillance Network (FoodNet) sites. Surveys were distributed to 1,630 LTCFs; 55% (865 of 1,568) of eligible facilities returned a completed questionnaire. Only three LTCFs completely followed national recommendations for prevention of Listeria monocytogenes contamination. Nine percent of LTCFs reported serving soft cheeses made from unpasteurized milk. Most LTCFs reported routinely serving ready-to-eat deli meats; however, few reported always heating deli meats until steaming hot before serving (only 19% of the LTCFs that served roast beef, 13% of those that served turkey, and 11% of those that served ham). Most LTCFs (92%) used pasteurized liquid egg products, but only 36% used pasteurized whole shell eggs. Regular whole shell eggs were used by 62% of facilities. Few LTCFs used irradiated ground beef (7%) or irradiated poultry products (6%). The results of this survey allowed us to identify several opportunities for prevention of foodborne illnesses in LTCFs. Some safety measures, such as the use of pasteurized and irradiated foods, were underutilized, and many facilities were not adhering to national recommendations on the avoidance of certain foods considered high risk for elderly persons. Enhanced educational efforts focusing on food safety practices and aimed at LTCFs are needed.

FoodNet: Overview of A Decade of Achievement

The Foodborne Diseases Active Surveillance Network (FoodNet) performs active, population-based laboratory surveillance for nine common foodborne pathogens and one syndrome in a catchment area of 44.5 million persons. FoodNet surveillance data are an important resource for examining trends in specific diseases over time. Population surveys and laboratory surveys have been used to estimate the burden of disease, for example that there are 38.6 cases of Salmonella infection for each reported case. FoodNet case-control studies have identified new risk factors for E. coli O157, Campylobacter, and several Salmonella serotypes. FoodNet sites have demonstrated the value of delivered stool kits for improving the rate of confirming an etiology in foodborne disease outbreaks. FoodNet helps build capacity for foodborne disease surveillance in participating sites and through close collaborations with PulseNet, EHS-Net, Global SalmSurv, and other partners.

Knowledge, Attitude, and Practice of the Use of Irradiated Meat among Respondents to the FoodNet Population Survey in Connecticut and New York

Irradiation of fresh meat to control microbial pathogens received approval from the federal government in February 2000. Food irradiation is a useful, albeit underutilized, process that can help protect the public from foodborne illnesses. The objective of this study was to determine consumer knowledge, attitudes, and practices toward irradiated meat products. Data were obtained from a single-stage random-digit dialing telephone survey of residents of the Foodborne Diseases Active Surveillance Network (FoodNet) sites conducted in 2002 to 2003, which included supplemental questions about food safety and irradiated meat for residents of the Connecticut and New York sites. Thirty-seven percent of 3,104 respondents knew that irradiated fresh meat was available for purchase; however, only 2% found the product where they shopped. Knowledge of product availability was significantly influenced by whether a respondent lived in a county with one or more grocery stores operated by chain A, which had actively promoted the sale of irradiated fresh ground beef during the survey period. In a logistic regression model, after adjusting for other factors, respondents living in a county with chain A were more likely to know that irradiated products could be purchased than respondents living in other counties (odds ratio 2.0; 95% confidence interval 1.5 to 2.5). This finding suggests that public education efforts by an individual grocery store chain can have an important effect on knowledge of irradiated food.

A population-based estimate of the substantial burden of diarrhoeal disease in the United States; FoodNet, 1996–2003

From 1996 to 2003, four 12-month population-based surveys were performed in FoodNet sites to determine the burden of diarrhoeal disease in the population. Acute diarrhoeal illness (ADI) was defined as > or =3 loose stools in 24 hours with impairment of daily activities or duration of diarrhoea >1 day. A total of 52840 interviews were completed. The overall weighted prevalence of ADI in the previous month was 5.1% (95% CI+/-0.3%), corresponding to 0.6 episodes of ADI per person per year. The average monthly prevalence of ADI was similar in each of the four survey cycles (range 4.5-5.2%). Rates of ADI were highest in those age <5 years. Of those with ADI, 33.8% (95% CI+/-2.7%) reported vomiting, 19.5% (95% CI+/-2.1%) visited a medical provider, and 7.8% (95% CI+/-1.4%) took antibiotics. Rates of ADI were remarkably consistent over time, and demonstrate the substantial burden placed on the health-care system.

Re-assessment of risk factors for sporadic Salmonella serotype Enteritidis infections: a case-control study in five FoodNet Sites, 2002-2003.

Active surveillance for laboratory-confirmed Salmonella serotype Enteritidis (SE) infection revealed a decline in incidence in the 1990s, followed by an increase starting in 2000. We sought to determine if the fluctuation in SE incidence could be explained by changes in foodborne sources of infection. We conducted a population-based case-control study of sporadic SE infection in five of the Foodborne Diseases Active Surveillance Network (FoodNet) sites during a 12-month period in 2002-2003. A total of 218 cases and 742 controls were enrolled. Sixty-seven (31%) of the 218 case-patients and six (1%) of the 742 controls reported travel outside the United States during the 5 days before the case's illness onset (OR 53, 95% CI 23-125). Eighty-one percent of cases with SE phage type 4 travelled internationally. Among persons who did not travel internationally, eating chicken prepared outside the home and undercooked eggs inside the home were associated with SE infections. Contact with birds and reptiles was also associated with SE infections. This study supports the findings of previous case-control studies and identifies risk factors associated with specific phage types and molecular subtypes.

Antimicrobial Resistance and Genetic Relatedness Among Salmonella from Retail Foods of Animal Origin: NARMS Retail Meat Surveillance

Salmonella isolates were recovered from a monthly sampling of chicken breasts, ground turkey, ground beef, and pork chops purchased from selected grocery stores in six participating FoodNet sites (Connecticut, Georgia, Maryland, Minnesota, Oregon, and Tennessee) in 2002 and an additional two sites in 2003 (California and New York). In 2002 and 2003, a total of 6,046 retail meats were examined, including 1,513 chicken breasts, 1,499 ground turkey samples, 1,522 ground beef samples, and 1,502 pork chops. Retail meat samples tested increased to 3,533 in 2003 as compared to 2,513 in 2002. Overall, six percent of 6,046 retail meat samples (n = 365) were contaminated with Salmonella, the bulk recovered from either ground turkey (52%) or chicken breast (39%). Salmonella isolates were serotyped and susceptibility tested using a panel of 16 antimicrobial agents. S. Heidelberg was the predominant serotype identified (23%), followed by S. Saintpaul (12%), S. Typhimurium (11%), and S. Kentucky (10%). Overall, resistance was most often observed to tetracycline (40%), streptomycin (37%), ampicillin (26%), and sulfamethoxazole (25%). Twelve percent of isolates were resistant to cefoxitin and ceftiofur, though only one isolate was resistant to ceftriaxone. All isolates were susceptible to amikacin and ciprofloxacin; however, 3% of isolates were resistant to nalidixic acid and were almost exclusive to ground turkey samples (n = 11/12). All Salmonella isolates were analyzed for genetic relatedness using pulsed-field gel electrophoresis (PFGE) patterns generated by digestion with Xba1 or Xba1 plus Bln1. PFGE fingerprinting profiles showed that Salmonella, in general, were genetically diverse with a total of 175 Xba1 PFGE profiles generated from the 365 isolates. PFGE profiles showed good correlation with serotypes and in some instances, antimicrobial resistance profiles. Results demonstrated a varied spectrum of antimicrobial resistance and PFGE patterns, including several multidrug resistant clonal groups among Salmonella isolates, and signify the importance of sustained surveillance of foodborne pathogens in retail meats.

Population-Based Incidence of Infection With Selected Bacterial Enteric Pathogens in Children Younger Than Five Years of Age, 1996–1998

Previous studies of bacterial enteric infections have suggested a disproportionate disease burden for children younger than 5 years of age. This study describes population-based incidence of culture-confirmed infections with 6 bacterial enteric pathogens in children younger than 5 years of age in the Foodborne Diseases Active Surveillance Network (FoodNet), 1996-1998. Cases were ascertained through active laboratory-based surveillance in Minnesota, Oregon and selected counties in California, Connecticut, Georgia, Maryland and New York. Twenty-one percent (5218 of 24,358) of infections were in children younger than 5 years of age, but this age group made up only 7% of the total person-years of observation. Among those younger than 5 years of age, the incidence (cases per 100,000 person-years) for each pathogen was: Salmonella, 55.3; Campylobacter, 43.4; Shigella, 32.7; E. coli O157, 10.3; Yersinia enterocolitica, 7.1; Listeria monocytogenes, 0.7. Incidence varied widely among the 7 FoodNet sites. This study confirmed a disproportionate disease burden in young children. Investigation of risk factors specific to this age group and review and enhancement of current prevention and control strategies for children younger than 5 years of age may reduce illness.

Prolonged diarrhea due to ciprofloxacin-resistant campylobacter infection.

Campylobacter causes >1 million infections annually in the United States. Fluoroquinolones (e.g., ciprofloxacin) are used to treat Campylobacter infections in adults. Although human infections with ciprofloxacin-resistant Campylobacter have become increasingly common, the human health consequences of such infections are not well described. A case-control study of persons with sporadic Campylobacter infection was conducted within 7 FoodNet sites during 1998-1999. The E-test system (AB Biodisk) was used to test for antimicrobial susceptibility to ciprofloxacin; ciprofloxacin resistance was defined as a ciprofloxacin minimum inhibitory concentration of > or =4 microg/mL. We conducted a case-comparison study of interviewed persons who had an isolate tested. Of 858 isolates tested, 94 (11%) were ciprofloxacin resistant. Among 290 persons with Campylobacter infection who did not take antidiarrheal medications, persons with ciprofloxacin-resistant infection had a longer mean duration of diarrhea than did persons with ciprofloxacin-susceptible infection (9 vs. 7 days [P=.04]). This difference was even more pronounced among the 63 persons who did not take antidiarrheal medications or antimicrobial agents (12 vs. 6 days [P=.04]). In a multivariable analysis-of-variance model, the persons with ciprofloxacin-resistant infection had a longer mean duration of diarrhea than did the persons with ciprofloxacin-susceptible infection (P=.01); this effect was independent of foreign travel. The association between ciprofloxacin resistance and prolonged diarrhea is consistent across a variety of analytical approaches. Persons with ciprofloxacin-resistant Campylobacter infection have a longer duration of diarrhea than do persons with ciprofloxacin-susceptible Campylobacter infection. Additional efforts are needed to preserve the efficacy of fluoroquinolones.

Farm visits and undercooked hamburgers as major risk factors for sporadic Escherichia coli O157:H7 infection: data from a case-control study in 5 FoodNet sites.

In 1996, active surveillance in 5 Foodborne Diseases Active Surveillance Network (FoodNet) sites revealed up to a 9-fold difference in Escherichia coli O157:H7 (O157) infection incidence between sites. A matched case-control study of sporadic O157 cases was conducted in these sites from March 1996 through April 1997. Case subjects were patients with non-outbreak-related diarrheal illness who had O157 isolated from their stool samples. Control subjects were healthy persons matched by age and telephone number exchange. Overall, 196 case patients and 372 controls were enrolled. O157 infections were associated with farm exposure, cattle exposure, eating a pink hamburger (both at home and away from home), eating at a table-service restaurant, using immunosuppressive medication, and obtaining beef through a private slaughter arrangement. Variations in cattle exposures may explain a part of the regional variability of O157 infection incidence. O157 control measures should focus on reducing risks associated with eating undercooked hamburger, dining at table-service restaurants, and farm exposures.

Population-based surveillance for Yersinia enterocolitica infections in FoodNet sites, 1996-1999: higher risk of disease in infants and minority populations.

Active surveillance for laboratory-confirmed Yersinia enterocolitica (YE) infections was conducted at 5 Foodborne Diseases Active Surveillance Network (FoodNet) sites in the United States during 1996-1999. The annual incidence averaged 0.9 cases/100,000 population. After adjusting for missing data, the average annual incidence by race/ethnicity was 3.2 cases/100,000 population among black persons, 1.5 cases/100,000 population among Asian persons, 0.6 cases/100,000 population among Hispanic persons, and 0.4 cases/100,000 population among white persons. Incidence increased with decreasing age in all race/ethnicity groups. Black infants had the highest incidence (141.9 cases/100,000 population; range, 8.7 cases/100,000 population in Minnesota to 207.0 cases/100,000 population in Georgia). Seasonal variations in incidence, with a marked peak in December, were noted only among black persons. YE infections should be suspected in black children with gastroenteritis, particularly during November-February. Culturing for YE should be part of routine testing of stool specimens by clinical laboratories serving populations at risk, especially during the winter months.

Breast-feeding decreases the risk of sporadic salmonellosis among infants in FoodNet sites.

Among the population of the Foodborne Diseases Active Surveillance Network (FoodNet) surveillance areas ("FoodNet sites") in 1996, children under 12 months of age had the highest incidence of sporadic salmonellosis. We conducted a case-control study in 5 FoodNet sites to identify risk factors for sporadic infant salmonellosis. A case patient was a child under 12 months of age with a laboratory-confirmed, nontyphoidal serogroup B or D Salmonella infection. Twenty-two case patients were matched with 39 control subjects by age and either telephone exchange or vital record birth list. In a multivariate analysis, case patients were more likely to have a liquid diet containing no breast milk than a liquid diet containing only breast milk (matched odds ratio, 44.5; P=.04). Case-patients were more likely to reside in a household where a member had diarrhea (matched odds ratio, 13.2; P=.01). To decrease their infants' risk of salmonellosis, mothers should be encouraged to breast-feed their infants. Caretakers of infants should learn about salmonellosis, hand washing, and safe preparation of formula and solid food.