Special Studies

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 case-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, links to study protocols and questionnaires, and article references can be accessed by clicking on the pathogen topic links below.

Campylobacter Studies

Case-control study of Campylobacter in infants, 2002

In 2002, FoodNet conducted a case-control study to identify behavioral, dietary, and medical risk factors for Campylobacter infection in infants (defined as 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.

An electronic copy of the questionnaire and protocol is not currently available. Please contact foodnet@cdc.gov to request a copy.

Reference:
  • Fullerton KE, Ingram A, Jones TF, Anderson BJ, McCarthy PV, Hurd S, Shiferaw B, Vugia DJ, Haubert N, Hayes T, Wedel S, Scallan E, Henao OL, Angulo FJ, EIP FoodNet Working. Sporadic Campylobacter infection in infants: a population-based surveillance case-control study. Ped Infect Dis. J 2007;26(1):19–24.

Campylobacter Case-Control Study, 1998

In 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.

An electronic copy of the questionnaire and protocol is not currently available. Please contact foodnet@cdc.gov to request a copy.

References:
  • Friedman CR, Hoekstra RM, Samuel M, Marcus R, Bender J, Shiferaw B, Reddy S, Ahuja SD, Helfrick DL, Hardnett F, Carter M, Anderson B, Tauxe RV. Risk factors for sporadic Campylobacter infection in the United States: a case-control study in FoodNet sites. Clin Infect Dis. 2004;38(Suppl 3):S286–296.
  • Kassenborg HD, Smith KE, Vugia DJ, Rabatsky-Ehr T, Bates MR, Carter MA, Dumas NB, Cassidy MP, Marano N, Tauxe RV, Angulo FJ; Emerging Infections Program FoodNet Working Group. Fluoroquinolone-resistant Campylobacter infections: eating poultry outside of the home and foreign travel are risk factors. Clin Infect Dis. 2004;38(Suppl 3):S279–284.
  • Nelson JM, Smith KE, Vugia DJ, Rabatsky-Ehr T, Segler SD, Kassenborg HD, Zansky SM, Joyce K, Marano N, Hoekstra RM, Angulo FJ. Prolonged diarrhea due to ciprofloxacin-resistant Campylobacter infection. J Infect Dis. 2004;150:1150–1157.

Cryptosporidium studies

Cryptosporidium Case-Control Study, 1999

In 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.

An electronic copy of the questionnaire and protocol is not currently available. Please contact foodnet@cdc.gov to request a copy.

Reference:
  • Roy SL, Delong SM, Stenzel SA, Shiferaw B, Roberts JM, Khalakdina A, Marcus R, Segler SD, Shah DD, Thomas S, Vugia DJ, Zansky SM, Dietz V, Beach MJ; Emerging Infections Program FoodNet Working Group. Risk factors for sporadic Cryptosporidiosis among immunocompetent persons in the United States from 1999 to 2001. J Clin Micro. 2004;42(7):2944–2951.

Listeria studies

Listeria monocytogenes Case-Control Study, 2000

In 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.

An electronic copy of the questionnaire and protocol is not currently available. Please contact foodnet@cdc.gov to request a copy.

Reference:
  • Varma JK, Samuel MC, Marcus R, Hoekstra RM, Medus C, Segler SD, Anderson BJ, Jones TF, Shiferaw B, Haubert N, Megginson M, McCarthy PV, Graves LM, Van Gilder T. Listeria monocytogenes infection from food in the regulatory era: A case-control study of risk factors for sporadic illness in the United States. Clin Infect Dis. 2007;44(4):521–528.

Salmonella studies

Cohort Study of Multi-Drug Resistant Salmonella, 2006

In 2006, FoodNet conducted a cohort study to investigate the impact of resistance to antimicrobial agents on clinical outcome of infection with nontyphoidal Salmonella.

Reference:
  • Krueger AL, Greene SA, Barzilay EJ, Henao O, Vugia D, Hanna S, Meyer S, Smith K, Pecic G, Hoefer D, Griffin PM. Clinical outcomes of nalidixic acid, ceftriaxone, and multidrug-resistant nontyphoidal salmonella infections compared with pansusceptible infections in FoodNet sites, 2006–2008. Foodborne Pathog Dis. 2014 May;11(5):335–41. doi: 10.1089/fpd.2013.1642. Epub 2014 Mar 11.

Case-control Study of Salmonella in Infants, 2002

In 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.

An electronic copy of the questionnaire and protocol is not currently available. Please use contact foodnet@cdc.gov to request a copy.

Reference:
  • Jones TF, Ingram A, Fullerton KE, et al. A case control study of Salmonella infection in infants, FoodNet, 2002–2004. Pediatrics. 2006;118(6):2380–2387.

Case-control study of Salmonella serotypes Enteritidis and Newport, 2002

In 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 serotype Newport strains resistant to third generation cephaolosporin antimicrobial agents was associated with eating undercooked eggs and beef.

An electronic copy of the questionnaire and protocol is not currently available. Please contact foodnet@cdc.gov to request a copy.

References:
  • Devasia RA, Varma JK, Whichard J, Gettner S, Cronquist AB, Hurd S, Segler S, Smith K, Hoefer D, Shiferaw B, Angulo FJ, Jones TF. Antimicrobial use and outcomes in patients with multidrug-resistant and pansusceptible Salmonella Newport infections, 2002–2003. Microbial Drug Resist. 2005;11(4):371–377.
  • Marcus R, Varma JK, Medus C, Boothe E, Anderson BJ, Crume TL, Fullerton KE, Moore MR, White PL, Lyszkowicz E, Voetsch AC, Angulo FJ, EIP FoodNet Working Group. Re-assessment of risk factors for sporadic Salmonella Enteritidis infections: a case-control study in five FoodNet Sites, 2002-2003. Epidemiol and Infect. 2007;135(1):84–92.
  • Varma JK, Marcus R, Stenzel SA, et al. Highly-resistant Salmonella Newport-MDRAmpC transmitted through the domestic U.S. food supply: a FoodNet case control study of sporadic Salmonella Newport infections, 2002–2003. Am J Infect Dis. 2006;194(2):222–230.

Cohort study of Salmonella Typhi, 2002

In 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.

An electronic copy of the questionnaire and protocol is not currently available. Please contact foodnet@cdc.gov to request a copy.

Reference:
  • Crump JA, Kretsinger K, Gay K, Hoekstra RM, Vugia DJ, Hurd S, Segler SD, Megginson M, Luedeman LJ, Shiferaw B, Hanna SS, Joyce KW, Mintz ED, Angulo FJ; Emerging Infections Program FoodNet and NARMS Working Groups. Clinical response and outcome of infection with Salmonella enterica serotype Typhi with decreased susceptibility to fluoroquinolones: a United States FoodNet multi-center retrospective cohort study. Antimicrob Agents Chemother. 2008 Apr;52(4):1278–84.

Salmonella studies

Case-control study of Salmonella Serogroups B and D, 1996

In 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.

An electronic copy of the questionnaire and protocol is not currently available. Please contact foodnet@cdc.gov to request a copy.

References:
  • Glynn MK, Reddy V, Hutwagner L, Rabatsky-Ehr T, Shiferaw B, Vugia DJ, Segler S, Bender J, Barrett TJ, Angulo FJ; Emerging Infections Program FoodNet Working Group. Prior antimicrobial agent use increases the risk of sporadic infections with multidrug-resistant Salmonella enterica serotype Typhimurium: a FoodNet case-control study, 1996–1997. Clin Infect Dis. 2004;38(Suppl 3):S227–236.
  • Hennessy TW, Cheng LR, Kassenborg H, Ahuja SD, Mohle-Boetani J, Marcus R, Shiferaw B, Angulo FJ. Group egg consumption is the principal risk factor for sporadic Salmonella serotype Heidelberg infections: a case-control study in FoodNet sites. Clin Infect Dis. 2004; 38(Suppl 3):S237–243.
  • Kimura AC, Reddy V, Marcus R, Cieslak PR, Mohle-Boetani JC, Kassenborg HD, Segler SD, Hardnett FP, Barrett T, Swerdlow DL. Chicken consumption is a newly identified risk factor for sporadic Salmonella enterica serotype Enteritidis infections in the United States: a case-control study in FoodNet sites. Clin Infect Dis. 2004;38(Suppl 3):S244–252.
  • Mermin J, Hutwagner L, Vugia D, Shallow S, Daily P, Bender J, Koehler J, Marcus R, Angulo FJ. Reptiles, amphibians, and human Salmonella infection: a population-based, case-control study. Clin Infect Dis. 2004;38(Suppl 3):S253–261.
  • Rowe SY, Rocourt JR, Shiferaw B, Kassenborg HD, Segler SD, Marcus R, Daily PJ, Hardnett FP, Slutsker L. Breast-feeding decreases the risk of sporadic salmonellosis among infants in FoodNet sites. Clin Infect Dis. 2004;38(Suppl 3):S262–270.

Shiga toxin-producing E. coli (STEC) studies

Shiga toxin-producing E. coli O157 (STEC) Genomics Study

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.

E. coli O157:H7 Cohort Study, 2006

In 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.

E. coli O157:H7 Case-Control Study, 2000

In 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.

An electronic copy of the questionnaire and protocol is not currently available. Please contact foodnet@cdc.gov to request a copy.

Reference:
  • Voetsch, AC, Kennedy MH, Keene WE, et al. Risk factors for sporadic Shiga toxin-producing Escherichia coli O157 infections in FoodNet Sites, 1999–2000. Epidemiol Infect. 2007;135(6):993–1000.

E. coli O157:H7 Case-Control Study, 1997

In 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.

An electronic copy of the questionnaire and protocol is not currently available. Please contact foodnet@cdc.gov to request a copy.

Reference:
  • Kassenborg HD, Hedberg CW, Hoekstra M, Evans MC, Chin AE, Marcus R, Vugia DJ, Smith K, Ahuja SD, Slutsker L, Griffin PM. 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. Clin Infect Dis. 2004;38(Suppl 3):S271–278.
Survey of Long Term Care Facilities, 2005

In 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.

An electronic copy of the questionnaire and protocol is not currently available. Please contact foodnet@cdc.gov to request a copy.

Reference:
  • Nelson JM, Bednarczyk R, Nadle J, Clogher P, Gillespie J, Daniels A, Plantenga M, Ingram A, Edge K, Furuno JP, Scallan E; FoodNet Emerging Infections Program Working Group. FoodNet survey of food use and practices in long-term care facilities. J Food Prot. 2008 Feb;71(2):365–72.

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