Co-infection with zoonotic Campylobacter and Salmonella
Kim O. Gradel,
We hypothesized that patients co-infected with thermophilic Campylobacter (TC) and non-typhoid Salmonella (NTS) had different characteristics than patients with TC or NTS mono-infections.
Population-based registry study comprising all TC/NTS co-infected patients (0-7 days between TC and NTS detection) and all first-time mono-infected TC or NTS patients in two Danish counties from 1991 through 2003. Data on recorded comorbidity were retrieved from the Danish Hospital Discharge Registry and data on one-year mortality from the Danish Civil Registration System.
A number of 114 patients were co-infected and 13,335 had mono-infections (6,768 TC [50.8%] and 6,567 NTS [49.2%]). The age distribution (median [1st-3rd quartile]: 26.2 [19.2-44.4] years for co-infected vs. 29.7 [17.6-48.2] years for mono-infected), comorbidity (15 co-infected (13.2%) vs. 1,611 mono-infected [12.1%]; OR [95% CI] = 1.1 [0.6-1.9]), and seasonal distribution (peak date and peak-to-trough ratio [95% CI]: 22 August and 2.6 [1.4-4.9] for co-infected vs. 28 August and 4.4 [4.1-4.8] for mono-infected) did not differ between the two patient groups. All co-infected and 13,100 mono-infected patients (98.2%) were alive after one year (p = 0.15). Co-infected patients had a higher ratio of exotic NTS serotypes (in contrast to Salmonella Enteritidis and S. Typhimurium) than mono-infected NTS patients (53.5% vs. 21.8%; OR [95% CI] = 4.1 [2.8-6.1]), whilst there were no differences between S. Enteritidis and S. Typhimurium (OR [95% CI] = 1.1 [0.6-2.0]).
Co-infected patients were not frailer than mono-infected patients. The differences in serotype distribution amongst NTS infected patients indicate that infection sources and behavioural factors (e.g., travel) are more important determinants of co-infection vs. mono-infection than baseline patient characteristics.