To detect detect intestinal schistosome infections, the World Health Organization recommends using the Kato-Katz technique, which analyzes slides of fecal matter. But the approach often misses people who are infected with only a low burden of parasites and, as a consequence, shed only a few eggs in fecal samples. Researchers have now analyzed the efficacy of other testing approaches in a setting with low parasite burden; their results appear in PLOS Neglected Tropical Diseases.

Schistosomiasis, or infection with the flatworm Schistosoma mansoni, affects more than 240 million people worldwide. In some countries -- including Brazil -- control programs have led to a significant reduction in the prevalence and parasite burden of endemic populations. However, in this setting it can be difficult to detect active infections since the Kato-Katz technique loses its sensitivity.

Stefan Geiger, of Brazil's Federal University of Minas Gerais, and colleagues examined 254 individuals in a moderate prevalence area of Northern Minas Gerais, Brazil, using four different approaches to test for intestinal schistosomiasis. The approaches were: the standard Kato-Katz technique, which analyzes slides from up to three fecal samples; a modified Helmintex method, which isolates eggs from 30 g. of feces using magnetic beads; a saline gradient, which cleans 500 mg of feces to detect eggs; and a rapid urine test (POC-CCA) which detects a secreted protein produced mainly by adult worms of S. mansoni.

When additional tests were used alongside the Kato-Katz method, the estimated prevalence of schistosomiasis in the population rose 2.3 times, from 20.4% to 45.9%. All methods lost their high sensitivity at low and very low intensity infections. The sensitivity of the POC-CCA (64.9%) was similar to the sensitivity of analyzing six Kato-Katz slides from three fecal samples. The best sensitivity was obtained with the Helmintex method (84%).

"In its present form, Helmintex is not applicable for large-scale screening due to the required sample size and the time-consuming sieving and sedimentation processes, but might be an adequate reference standard or gold standard for the evaluation of newly developed, field-based diagnostic tests," the researchers say. "We believe that a combination of methods has to be implemented since the schistosomiasis control programs in different regions of the world are moving from morbidity control towards transmission control and elimination."