Intestinal parasites in Cambodians: comparison of diagnostic methods used in screening refugees with implications for treatment of populations with high rates of infestation.

We performed a retrospective review of screening parasitology examinations on a Cambodian refugee population served by an urban neighborhood health center. Five-hundred twenty of 1084 patients were examined for ova and parasites either by purged stool, which was examined immediately, or preserved stool, examined at a teaching hospital and proprietary laboratories. Overall, 335 (64 percent) of the tested patients had at least one parasite. The prevalence of infection varied by test technique (purged stool examined immediately, 86 percent; preserved stool examined at a hospital, 65 percent; preserved stool sent to a proprietary laboratory, 31 percent, P less than 0.01). In this population where Entamoeba histolytica infection was 44 percent as measured by the purged warm stool technique, the cold preserved stool test had a measured relative sensitivity of 33 percent. Assuming a selectivity of 99 percent, it would take eight negative tests to reach a greater than 95 percent negative predictive value. The high rate of intestinal carriage of pathogenic parasites in this population and the insensitivity of commonly available diagnostic tests make routine presumptive treatment of intestinal parasites an option when the purged stool examination is unavailable.