Sensitivity and specificity of leukocyte count in feces as a predictor of stool culture positivity for Samonella or Shigella

In most studies of fecal leukocyte counts as predictors of the result of stool cultures the sensitivity and specificity were not determined. Objective: to evaluate fecal leukocyte counts as a predictor of the presence of Salmonella and Shigella. Design: a descriptive, cross section study was carried out in 905 stool cultures at a university hospital in Medellin, Colombia. Results for Salmonella and Shigella were taken as the gold standard to evaluate the sensitivity and specificity of fecal leukocyte counts. Results: sensitivity and specificity, according to the level of the count, were, respectively: 1-5 leukocytes: 89.2% and 57.1%; 6-10 leukocytes: 86.2% and 52.8%; 11-20 leukocytes: 77.7% and 62.7%; 21-30 leukocytes: 63.9% and 76.3%; 31-50 leukocytes: 45.2% and 85.5%; more than 50 leukocytes: 28.3% and 90.9%. The area under the curve was 0.7699 (CI 95%: 0.7275-0.8123). Conclusions: sensitivity decreased and specificity increased with higher counts of fecal leukocytes. Low specificity with the lesser values of leukocyte counts may be due to either the presence of enteroinvasive pathogens other than Salmonella and Shigella, or to non-infectious diarrheal disease.