At a glance
FoodNet conducts studies to examine the importance of various possible exposures (such as specific foods) and practices (such as food preparation and handling) as contributors to foodborne infections.
Overview
Although foodborne outbreaks are common, approximately 95% of foodborne infections occur as sporadic (non-outbreak) cases. It is difficult to determine what specific exposure caused a person with a sporadic infection to become ill. However, risk factors can be explored through population-based studies.
Studies are conducted to examine the importance of various possible risky exposures (such as specific foods) and practices (such as food preparation and handling practices) as contributors to illness caused by specific pathogens.
Cases of infections with the pathogens under study are ascertained through routine FoodNet surveillance. FoodNet staff contact patients and healthy controls (if a case-control study is being performed) to administer a questionnaire. Studies may also include molecular subtyping or antimicrobial resistance testing of patient isolates.
Study summaries and article references can be found below. Electronic copies of the questionnaires and protocols for these studies can be obtained by contacting foodnet@cdc.gov.
Studies
Case-control study of Campylobacter in infants (2002)
FoodNet conducted a case-control study to identify behavioral, dietary, and medical risk factors for Campylobacter infection in infants (babies less than 12 months old).
Risk factors included consuming reconstituted formula or well water, living on or visiting a farm, having a pet with diarrhea, and riding in a shopping cart next to meat or poultry. Breastfeeding protected against infection.
Campylobacter case-control study (1998)
FoodNet conducted a case-control study to determine risk factors for Campylobacter infection. Food-specific risk factors identified include consuming chicken or non-poultry meat prepared at a restaurant. Non-food risk factors included contact with farm animals, animal stool, and pet puppies.
Isolates from a subset of cases enrolled in this study had antimicrobial susceptibility testing; 11% were resistant to the fluroquinolone ciprofloxacin. Risk factors for fluroquinolone-resistant Campylobacter infection included consumption of chicken or turkey in a commercial establishment and recent foreign travel. In addition, ciproflaxacin-resistant Campylobacter was associated with prolonged diarrhea.
Cryptosporidium case-control study (1999)
FoodNet conducted a case-control study to determine sources and risk factors for Cryptosporidium infection. Objectives included estimating the burden of illness associated with Cryptosporidium infection and determining the proportion of laboratory-confirmed sporadic infections that could be attributed to consuming foods or water, or to contact with recreational water or farm animals.
Risk factors identified included international travel, contact with cattle, contact with persons >2 to 11 years of age with diarrhea, and freshwater swimming. Eating raw vegetables protected against infection.
Listeria monocytogenes case-control study (2000)
FoodNet conducted a case-control study to identify risk factors for sporadic listeriosis and to describe the spectrum of illness. Results identified two new possible risk factors: eating melons at a commercial establishment and eating hummus prepared in a commercial establishment.
Cohort study of multi-drug resistant Salmonella (2006)
FoodNet conducted a cohort study to investigate the impact of resistance to antimicrobial agents on clinical outcome of infection with nontyphoidal Salmonella.
Case-control Study of Salmonella in Infants (2002)
FoodNet conducted a case-control study to identify risk factors for Salmonella infection in infants less than 2 months old. Risk factors identified included exposure to reptiles, attending daycare with a child with diarrhea, consuming meat, consuming reconstituted infant formula, and riding in a shopping cart next to meat or poultry. Breastfeeding was protective.
Case-control study of Salmonella serotypes Enteritidis and Newport (2002)
FoodNet conducted a case-control study of Salmonella Enteritidis (SE) and Salmonella Newport infections. Among persons who had not recently traveled internationally, SE infections were associated with eating chicken prepared outside the home and undercooked eggs inside the home. SE infections were also associated with contact with birds and reptiles.
Infection with Salmonella Newport strains resistant to third generation cephalosporin antimicrobial agents was associated with eating undercooked eggs and beef.
Cohort study of Salmonella Typhi (2002)
FoodNet conducted a retrospective cohort study to examine the impact on clinical outcome of reduced susceptibility to fluoroquinolones in Salmonella serotype Typhi infection. Results showed that patients infected with a strain with reduced susceptibility to fluoroquinolones had more prolonged fever and more frequent treatment failure.
Case-control study of Salmonella Serogroups B and D (1996)
FoodNet conducted a case-control study to identify risk factors for non-typhoidal Salmonella serogroup B or D infection. Reptile contact was associated with infection, and breast feeding protected against it. Eating chicken and undercooked eggs were associated with Salmonella serotype Enteritidis and Salmonella serotype Heidelberg infections. Antimicrobial use in the month before illness was associated with multi drug-resistant Salmonella serotype Typhimurium DT104 infection.
STEC cohort study (2006)
FoodNet began a 4-year cohort study among persons diagnosed with E. coli O157:H7 infection to describe antibiotic exposure and the risk of developing hemolytic uremic syndrome (HUS). Subject enrollment and data collection is complete; data analyses are ongoing.
STEC genomics study (2006)
People enrolled in the E. coli O157:H7 cohort study (above) were also offered enrollment in a genomics study of genetic factors related to development of HUS. Subject enrollment and data collection is complete; data analyses are ongoing.
STEC case-control study (2000)
FoodNet conducted a second E. coli O157 case-control study. This study included subtyping of isolates by pulsed-field gel electrophoresis (PFGE).
Infection was associated with eating pink hamburgers, drinking untreated surface water, and living on or visiting a cattle farm. Eating fruits and vegetables protected against infection.
STEC case-control study (1997)
FoodNet conducted a case-control study to determine risk factors for E. coli O157:H7 infection.
The study found that visiting a farm, living on or visiting a farm that had cattle, eating pink hamburger (either at home or away from home), eating at a table-service restaurant, and obtaining beef through a private slaughter arrangement were the principal risk factors.
Survey of long-term care facilities (2005)
FoodNet conducted a survey of long-term care facilities to assess food preparation practices. The survey evaluated included general food preparation; the types of beef, poultry, eggs, and other foods provided to residents; and policies on use of irradiated beef, irradiated poultry, and pasteurized shell eggs.
Results showed that only three long-term care facilities of 865 surveyed completely followed national recommendations for prevention of Listeria monocytogenes contamination.