Increased prescription rate of antibiotics prior to non-typhoid Salmonella infections: A one-year nested case-control study

We conducted a nested case-control study of antibiotic consumption 1 y prior to a non-typhoid Salmonella (NTS) infection. We included all 1882 NTS patients diagnosed in 1994-2003 in North Jutland County, Denmark, and for each case we retrieved 10 controls among all residents in the county, matched for the specimen date, gender, and age. Antibiotic redemptions were retrieved from a countywide prescription database. Being a marker of the infection, redemptions within 1 week before NTS infection were excluded. The subject's last antibiotic redemption, if any, was the binary outcome in a conditional logistic regression model, and we adjusted for comorbidity based on previous hospital discharge diagnoses. In the y up to the NTS episode, 42.0% of cases and 28.5% of controls redeemed antibiotics (adjusted odds ratio (OR) 1.59, 95% confidence intervals 1.43-1.77). The OR was constant up to 20 weeks before the NTS episode and increased continuously thereafter. The higher antibiotic consumption during the entire y may imply that NTS patients are frailer than the general population. The increased OR in the weeks close to the NTS infection are consistent with alterations in the intestinal microflora being involved in acquiring an NTS infection.