Assessing Risk Factors of Sporadic Campylobacter Infections: A State-Wide Case-Control Study in Arizona

BACKGROUND:  Various case-control studies of sporadic Campylobacter infections have been conducted, although predominately among people of non-Hispanic ethnicity.  Common risk factors include consumption of chicken, unpasteurized dairy products, untreated water, contact with animals and travel history.  In Arizona, rates of campylobacteriosis have been higher than the national average for the past decade, with particularly high rates among Hispanics.  In 2010, state and county health departments and a state University collaborated to conduct a statewide case-control study aimed to determine whether risk factors differ in a region of the United States with a more ethnically diverse case population. 

METHODS:  Epidemiologists administered extended questionnaires for each case identified through routine surveillance that was not part of a known outbreak.  Controls were recruited matched by age group, gender and residence.  Ultimately, due to low matching efficiency, random effects logistic regression, rather than conditional regression, was chosen to keep all case data in the analyses.  A final multivariate model was built using this technique.  Initial analyses found both Hispanic ethnicity and travel to be an increased risk of disease.  To determine if Hispanic was a surrogate for travel or an independent risk factor, a joint variable was created.

RESULTS:  During the study period, 781 laboratory culture-confirmed cases of C.jejuni were reported; 424 cases were eligible for the study; of these 110 cases participated (26%).  61 control interviews were completed, resulting in 37 matched sets (a set consisted of a case and either one or two matched controls).  The final multivariate model found the statistically significant risk factors to be: eating cantaloupe (OR=7.64), handling raw poultry (OR=4.88) and eating queso fresco (OR=7.11).  Protective risk factors included washing the cutting board following raw meat contact (OR=0.14), and consuming blueberries (OR=0.15) or roast beef (OR=0.10).  In addition, compared to Non-Hispanic/Non-Travelers, the highest risk group were Hispanic/Non-Travelers (OR=7.27), and Hispanic/Travelers (OR=5.87-not significant).  Non-Hispanic/Travelers were decreased odds with a non-significant OR=0.59 although the sample size was very small (n=4).   

CONCLUSIONS:  Results of this study suggest Hispanics have higher odds of disease, likely due to differential exposures.  In addition to common risk factors, consumption of cantaloupe was identified as a significant risk factor - a food item linked to outbreaks of other enteric diseases, but not commonly associated with Campylobacter infection.  The results from this study will help to inform public health officials of the varying risk factors for Campylobacter in this region and beyond and can be used to modify routine questionnaires.