Antimicrobial use: a risk factor or a protective factor for acquiring campylobacteriosis?

Background. It is well acknowledged that the use of antimicrobial drugs in food animals leads to antimicrobial drug resistance in foodborne bacteria such as Campylobacter; however, the role of human antimicrobial usage is much less investigated. The aim of this study was to quantify the odds of campylobacteriosis conferred by human consumption of fluoroquinolones and macrolides. Methods. We conducted a registry-based retrospective case-control study on 31 669 laboratory-confirmed cases of campylobacteriosis between 1999 and 2005 in Denmark. Data were obtained from several Danish databases: the National Registry of Enteric Pathogens, the Danish Civil Registration System, the Danish National Prescription Database, and the Integrated Database on Labor Market Research. Odds ratios (OR) for campylobacteriosis were calculated by conditional logistic regression. Results. The risk of campylobacteriosis was reduced 1 month after exposure to macrolides (OR, 0.72; 95% confidence interval [CI], 0.56-0.92). Macrolide exposure 1 month to 2 years before infection was associated with an increased risk of a Campylobacter diagnosis (OR, 1.5; 95% CI, 1.4-1.6). A history of fluoroquinolone use was also associated with increased risk (OR, 2.5; 95% CI, 1.8-3.5). This risk was higher for resistant isolates than for susceptible ones. Conclusions. Treatment with macrolides may protect against Campylobacter infection for a limited period of time, possibly due to the antibacterial effects of the drug or its metabolites. Fluoroquinolone treatment confers increased risk, probably due to a combination of competitive and selective effects, similar to what has been observed for nontyphoid Salmonella infection.