1. E. coli O157 Case-Control Study (1996-1997, 1999-2000)

CEIP conducted two population-based case-control studies to explore risk factors for sporadic E. coli O157 infection in 1996-1997 and in 1999-2000. Cases were identified through active surveillance for laboratory-confirmed E. coli O157. Controls were matched to cases on age and telephone exchange and identified through sequential digit dialing. For the first study, 196 cases and 372 controls were enrolled. The study identified eating a pink hamburger, eating at a table-service restaurant, farm exposure, and cattle exposure as significant risk factors. A total of 283 cases and 534 controls were enrolled in the second risk factor study from seven participating FoodNet sites. The study found similar risk factors for sporadic E. coli O157, including eating undercooked ground beef and exposure to surface waters and farms.

2. Neonatal Infections Case-series Study (1996-2001)

CEIP led a study with participation from six FoodNet sites to describe clinical features of illness with foodborne pathogens among neonates and to explore possible risk factors in the first seven days of life. 11 of 11 eligible cases (100%) were enrolled and medical charts abstracted by CEIP staff. CEIP also led the analysis of data on the 54 total cases and presented findings at the Infectious Disease Society of America Annual Meeting in October 2003.

3. Case-Control Study of Shigellosis in San Francisco (1998-1999)

CEIP conducted a population-based case-control study of shigellosis in adults in San Francisco during the period 1998–1999. Cases of Shigella infection were identified through laboratory-based active surveillance conducted by CEIP. 76 case-patients were matched by sex with 146 control subjects. Exposure data were collected on established risk factors, sexual practices, and HIV infection status. From the multivariable analysis, for men, shigellosis was associated with sex with men (odds ratio [OR], 8.24; 95% confidence interval [CI], 2.70–25.2), HIV infection (OR, 8.17; 95% CI, 2.71–24.6), direct oral-anal contact (OR, 7.50; 95% CI, 1.74–32.3), and foreign travel (OR, 20.0; 95% CI, 5.26–76.3), with population-attributable fractions of 0.72, 0.42, 0.31, and 0.18, respectively. For women, shigellosis was associated only with foreign travel (OR, 21.0; 95% CI, 2.52–899), with a population-attributable fraction of 0.37. Among men who have sex with men, shigellosis is predominantly a sexually transmitted disease, with direct oral-anal contact conferring the highest risk and HIV infection likely contributing to increased host susceptibility.

4. Enhanced Yersinia Surveillance (California only, 1998-2000)

Due to the large number of Yersinia enterocolitica cases in California and their diverse racial/ethnic distribution,  CEIP staff interviewed 59 Y. enterocolitica case-patients with a hypothesis-generating questionnaire from 1998 to 2000. In addition, 22 Y. enterocolitica isolates were submitted to MDL for sero- and bio-typing. 17 (77%) of the isolates were serotype O:3, suggesting the involvement of pork products. Results from this project may be used to inform future studies of Y. enterocolitica in California, particularly among communities of color.

5. Cryptosporidium Case-Control Study (1999-2001)

This study investigated risk factors for sporadic infection with Cryptosporidium among immunocompetent persons during 1999-2001. Over the two-year period of data collection, 282 laboratory-confirmed cases and 490 age-matched controls were enrolled, including 26 cases and 62 controls in California. Analysis of the pooled data for all FoodNet sites identified international travel as a significant risk factor. Other risk factors included contact with cattle, contact with children age 2-11 years with diarrhea, and freshwater swimming. A separate analysis of the data collected through California FoodNet showed that international travel was the primary risk factor for the urban population in the San Francisco Bay Area.

6. Physicians Survey (2000)

Randomly selected physicians practicing in the CEIP catchment area were mailed questionnaires to investigate the role of physicians as food-safety educators. CEIP received 106 completed questionnaires. Of the 1100 enrolled physicians in all FoodNet sites, only 331 (30%) of the respondents reported providing food-safety information to their patients.

7. Listeria Case-Control Study (2000-2003)

The goal of this case-control study was to identify dietary and behavioral risk factors for listeriosis. Controls were identified by clinicians and were matched based on underlying medical condition and broad age groups. The study started in California with specimen collection date March 15, 2000, and ended with specimen collection date March 15, 2003. During the study period, 169 cases were enrolled, including 24 cases from California. In addition, 376 controls, including 50 controls from California, were successfully enrolled. Multivariate analysis of study data showed that eating melons and eating hummus were independently associated with infection with Listeria.

8. Infant Salmonellosis and Campylobacteriosis Case-Control Study (2002-2004)

The goals of this study were to identify behavioral, dietary, and medical risk factors for infection of infants under 365 days old with Salmonella or Campylobacter, and to describe the epidemiologic and medical characteristics of infants with these infections. From May 1, 2002 to April 30, 2004, 442 salmonellosis cases, 123 campylobacteriosis cases, and 928 controls were interviewed and enrolled in the study. CEIP contributed substantially to the project’s ability to explore infant illness in Asian communities by contributing 58% of all Asian Salmonella cases, 64% of all Asian Campylobacter cases, and 63% of all Asian controls.

Our study found several important risk factors for Campylobacter infection, including the previously-undocumented risk factor of riding in a shopping cart next to meat or poultry (odds ratio [OR], 4.0; 95% confidence interval [CI], 1.2 – 13.0) among infants 0 – 6 months of age. Risk factors among infants 7 – 12 months of age included visiting or living on a farm (OR, 6.2; CI, 2.2 – 17.0), exposure to a pet with diarrhea (OR, 7.6; CI, 2.1 – 28.0), and eating fruits or vegetables prepared at home (OR, 2.5; CI, 1.2 – 4.9). As in previous studies, breastfeeding was a protective factor for Campylobacter infection among children 0 – 6 months of age (OR, 0.2; CI, 0.1 – 0.6). Recommended preventive measures included breastfeeding and keeping infants away from pets with diarrhea.

Our analysis of Salmonella infection among infants found that riding in a shopping cart next to meat or poultry was a risk factor for illness. In addition, exposure to reptiles, eating concentrated liquid infant formula, and international travel were identified as important risk factors. As with our analysis of Campylobacter infection, infants with Salmonella infection were less likely to have been breastfed.

9. Case-Control Study of Salmonella Newport (2002-2003)

CEIP and its FoodNet partners implemented the first multi-state investigation of S. Newport infections in the United States to identify behavioral, dietary, and medical risk factors associated with S. Newport. From 2002 to 2003, 215 laboratory-confirmed S. Newport cases and 1154 healthy controls were enrolled in the study. The study found substantial evidence of the role of the U.S. food supply in the transmission of multidrug-resistant (MDR) S. Newport. Eating uncooked ground beef (OR, 7.8 [95% confidence interval {CI}, 1.4–44]) and runny scrambled eggs or omelets prepared in the home (OR, 4.9 [95% CI, 1.3–19]) were associated with illness with MDR S. Newport. Use of antimicrobial agents prior to illness was also an important risk factor (odds ratio [OR], 5.0 [95% CI, 1.6–16]). Recommendations included food-safety educational efforts regarding thorough cooking of ground beef and poultry products and education of physicians regarding prudent use of antimicrobial therapy.

10. Prospective Viral Study (2002-2003)

The goal of this project was to better describe the role of caliciviruses (specifically norovirus) in foodborne disease and the associated epidemiologic and clinical profiles. A contracted medical courier facilitated the delivery and pickup of self-contained stool specimen collection kits directly to case-patients in outbreak settings for timely and proper specimen collection. During October 2002 to June 2003, the stool collection kits were deployed in 21 of 29 outbreaks (72%) reported to CEIP. Norovirus was confirmed by polymerase chain reaction (PCR) in 13 (57%) of these outbreaks. Data from this study were pooled with data from two other FoodNet sites and results were published in Clinical Infectious Diseases. The study demonstrated that delivery of kits to and from patients could substantially increase the percentage of outbreaks in which etiology is known.

11. Retrospective Cohort Study of Salmonella Typhi (1999-2000)

A retrospective cohort study was conducted to evaluate the affect of nalidixic acid-resistance on clinical outcome among persons with typhoid fever. Medical records were abstracted for all hospitalized S. Typhi cases with bloodstream or bone marrow infection identified in the FoodNet catchment area from 1999 to 2002. Data from medical chart abstraction were linked to corresponding laboratory test results and existing surveillance data. Medical chart abstractions were successfully completed for all 20 (100%) eligible cases in the California FoodNet site. Data were pooled from seven participating FoodNet sites for analysis. CEIP contributed 35% of the total eligible cases.

12. Survey of Clinical Laboratory Practices for Campylobacter Isolation and Identification (2005-2006)

The purpose of this project was to determine whether the variation in incidence of laboratory-confirmed Campylobacter infection by EIP site was associated with differences in laboratory techniques for Campylobacter isolation at each site. A standardized questionnaire was developed to collect detailed information from the lead microbiologists at clinical laboratories regarding their routine practices to isolate Campylobacter from stool specimens. The questionnaire included routine use of transport media, enrichment, or filtration, choice of selective agar, and incubation duration and temperature, any of which could affect isolation rates for Campylobacter and therefore affect laboratory-confirmed incidence. Questionnaires were mailed in August 2005 and completed surveys were collected until May 2006. A total of 26 (84%) of the 31 public health and private laboratories participating in CEIP FoodNet surveillance completed the questionnaires. Preliminary data of 499 enrolled laboratories in 10 FoodNet sites were summarized and presented at the 2006 International Conference on Emerging Infectious Diseases. The study showed that there were substantial differences in methods such as routine culturing, length of incubation, and use of transport media and most laboratories did not adhere to existing guidelines, likely resulting in under diagnosis.

13. FoodNet Survey of Food Use and Practices in long-term care facilities (2005)

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 food safety. 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 FoodNet sites. Surveys were distributed to 1,630 LTCFs and 55% (865 of 1,568) of eligible facilities returned a completed questionnaire. 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.

14. STEC Physician Survey (2009)

Shiga toxin-producing Escherichia coli (STEC) infections cause acute diarrheal illness and sometimes life-threatening hemolytic uremic syndrome (HUS). E. coli O157 is the most common STEC, although the number of reported non-O157 STEC infections is growing with the increased availability and use of enzyme immunoassay testing, which detects the presence of Shiga toxin in stool specimens. Prompt and accurate diagnosis of STEC infection facilitates appropriate therapy and may improve patient outcomes. 2400 surveys were mailed  to physicians in eight FoodNet site catchment areas to assess their knowledge and practices regarding STEC testing, treatment, and reporting, and their interpretation of Shiga toxin test results. Of 1102 completed surveys, 955 were included in this analysis. Most  physicians (83%) reported often or always ordering a culture of bloody stool specimens, 49% believed that their laboratory routinely tested for STEC O157, and 30% believed that testing for non-O157 STEC was also included in a routine stool culture. 42% of physicians were aware that STEC, other than O157, can cause HUS, and 34% correctly interpreted a positive Shiga toxin test result. All STEC knowledge-related factors were strongly associated with correct interpretation of a positive Shiga toxin test result. Identification and management of STEC infection depends on laboratories testing for STEC and physicians ordering and correctly interpreting results of Shiga toxin tests. Although overall knowledge of STEC was low, physicians who had more knowledge were more likely to correctly interpret a Shiga toxin test result. Physician knowledge of STEC may be modifiable through educational interventions.