Is the prevalence of Clostridium difficile in animals underestimated?

Reported prevalence rates of Clostridium difficile infection in animals differ considerably depending on the nature of the study and the population surveyed. The methods used to recover this organism from faecal samples may account for some of the prevalence variation. The objective of this study was to assess the performance of two different methods of detecting C. difficile in animal faeces in comparison with a conventional isolation procedure ('ethanol shock' of faecal samples followed by culture on a single plate of solid selective medium). Samples were obtained from two populations of pigs where the expected prevalence rate of C. difficile infection was anticipated to differ, namely, 'high prevalence' (<7-day old piglets) and 'low prevalence' (2-3-month old pigs). The first alternative detection method required culturing faecal samples on 10 (instead of one) plate of solid selective medium after ethanol shock, while the second method included an intermediate enrichment step in selective broth prior to ethanol shock and subsequent plating. Both alternative methods considerably increased bacterial recovery in tested samples from both surveyed populations and highlighted the existence of a considerable proportion (≥ 22%) of false negatives. The results confirm previous suggestions that the procedure used to isolate C. difficile can have a significant impact on prevalence data for this pathogen.