Non-O157 STEC Case-Control
Background: Each year many Shiga toxin-producing E. coli (STEC) infections occur in the United States, ranging in severity from mild diarrhea, to hemorrhagic colitis and in some cases, life-threatening hemolytic uremic syndrome (HUS). Non-O157 STEC are a diverse group that includes all Shiga toxin-producing E. coli of serogroups other than O157. Over 50 STEC serogroups are known to have caused human illness; in the United States, over 70% of strains isolated from humans belong to one of six serogroups (O26, O111, O103, O121, O45, and O145); each serogroup may contain several serotypes. Little is known about the specific risk factors for infections due to non-O157 STEC serogroups. Better identification of exposures that lead to these infections could assist in designing effective control and prevention measures.
Objectives: The primary objectives of the study are to identify behavioral, environmental, dietary, and medical risk factors for sporadic non-O157 STEC infections, both as a group and for at least the three most common individual serogroups, and by the most common virulence profiles, and to estimate the proportion of disease risk attributable to specific risk factors (population attributable fraction or PAF).
Design: Matched case-control study.
Participants: A case is defined as isolation of a non-O157 STEC and no isolation of E. coli O157 from a clinical specimen collected from an ill person residing in a FoodNet site catchment area during that site’s 36 month study period. We will attempt to enroll three age- and county-matched controls for each enrolled case. Once a case-patient has been interviewed, controls should be enrolled as soon as possible.
Data collection: Cases and controls will be interviewed by the research coordinator over the phone. The questionnaire covers demographic characteristics, clinical history, and specific food, water, animal, person-to-person, and environmental exposures. Isolates of non-O157 STEC from all cases enrolled into the study will be sent from participating state health department laboratories to CDC E. coli Reference laboratory for additional characterization including complete serotyping and assessment of virulence factors.
Outcome and analysis: Descriptive analyses will be conducted to evaluate how patient demographic and clinical features vary by non-O157 STEC serogroup and by virulence factor profiles. Potential behavioral, environmental, dietary, and medical risk factors will be assessed through calculation of odds ratios and population attributable fraction (PAF); risk factors will be evaluated for all non-O157 STEC collectively as a single group, and individually for the most common serogroups and virulence factor profiles. Multivariate modeling of potential risk factors, confounders and effect modifiers may be performed. Finally, we will compare demographic characteristics, clinical features, and reported exposures between patients with and without land-line telephones in their primary residence and between patients with mixed infections and patients with single etiology infections.
Sponsor: U.S. Centers for Disease Control and Prevention (CDC)
Start date: January 2012
Expected end date: December 2015
To see all Oregon Emerging Infections Program special studies go to EIP special studies.