A pilot study to evaluate an efficient testing strategy for surveillance of Schistosoma Mansoni infection

Abstract

Introduction: Control strategies for schistosomiasis depend on the understanding of the population specific magnitude of the infection. We present pilot results of a testing strategy suggested by theoretical statistical investigation that lowers cost yet retains similar accuracy profile as the standard Kato-Katz technique.
Methods: We use an estimator of the prevalence of Schistosoma Mansoni based on pooled stool samples. To test this estimator in real-time, we collected 100 samples of stools from rural Tanzania. All samples were first subjected to standard 41.7mg Kato-Katz technique and then again to two rounds of 25 pooled four-sample tests (11mg from each of the 4 samples). Separate technicians blinded to the other results were used for the standard and pooled tests.
Results: Of the 100 individual standard Kato-Katz tests, 31 tested positive. Estimate of the prevalence from the individual testing was 0.31 with a 95% confidence interval of (0.05, 0.23). Of the first set of 25 four-sample pool Kato- Katz, 19 tested positive. Similarly, 19 also tested positive in the second set of 25 pools. Thus, the two pooled estimates of prevalence were the same, and yielded a prevalence estimate of 0.30 based on the Maximum likelihood estimator and 0.29 based on the less biased Burrows’ estimator. The mean squared error associated with the Burrow’s estimator was approximately 0.00485. Thus, an approximate 95% confidence interval around this estimate was (0.15, 0.43).
Conclusion: Inference drawn from the theoretical and pilot prevalence estimate of Schistosoma Mansoni from 25 four– sample pooled Kato-Katz tests is as accurate as it is from 50 single-samples standard tests. The proposed pooled strategy could therefore be more efficient and cost effective surveillance strategy especially in resource constrained countries where the burden of infection is high. This method would guide timely decision making and have the potential to increase the intended treatment coverage.

Keywords: Schistosoma Mansoni, KatoKatz, testing strategy, Surveillance, Tanzania