The effect of fecal sample weight on detection of Salmonella enterica in swine feces

The effect of different fecal sample weights on the detection of Salmonella enterica in swine feces was examined. Sample weights evaluated were rectal swabs and fecal samples weighing 1 g, 10 g, and 25 g. Comparisons were mad e on matched fecal samples obtained from individual pigs housed on 2 commer cial swine farms in North Carolina. Relative sensitivity (number of positiv e pigs per fecal weight category/number positive in all weight categories) increased (P < 0.001) with fecal sample weight, and ranged from 9% for rect al swabs to 78% for 25-g samples. Stomaching of fecal samples did not affec t detection of S. enterica. These observations demonstrate that fecal sampl e weight can markedly influence estimates of prevalence of S. enterica in e pidemiologic studies. Failure to consider the imperfect sensitivity of bact erial culture in the design and interpretation of epidemiologic studies wil l lead to underestimation of prevalence and reduced power to detect the pre sence of S. enterica-infected herds.