Occurrence of Strongyloides stercoralis in Yunnan Province, China, and Comparison of Diagnostic Methods

Abstract

Background

Strongyloides stercoralis is a neglected soil-transmitted helminth species, and there is a lack of parasitologic and epidemiologic data pertaining to this parasite in China and elsewhere. We studied the local occurrence of S. stercoralis in a village in Yunnan province, China, and comparatively assessed the performance of different diagnostic methods.

Methodology/Principal Findings

Multiple stool samples from a random population sample were subjected to the Kato-Katz method, an ether-concentration technique, the Koga agar plate method, and the Baermann technique. Among 180 participants who submitted at least 2 stool samples, we found a S. stercoralis prevalence of 11.7%. Males had a significantly higher prevalence than females (18.3% versus 6.1%, p = 0.011), and infections were absent in individuals <15 years of age. Infections were only detected by the Baermann (highest sensitivity) and the Koga agar plate method, but neither with the Kato-Katz nor an ether-concentration technique. The examination of 3 stool samples rather than a single one resulted in the detection of 62% and 100% more infections when employing the Koga agar plate and the Baermann technique, respectively. The use of a mathematical model revealed a ‘true’ S. stercoralis prevalence in the current setting of up to 16.3%.

Conclusions/Significance

We conclude that S. stercoralis is endemic in the southern part of Yunnan province and that differential diagnosis and integrated control of intestinal helminth infections needs more pointed emphasis in rural China.

Author Summary

An estimated 30 million to 100 million people are infected with the parasitic worm Strongyloides stercoralis, the causative agent of strongyloidiasis, and yet this is a neglected tropical disease. The diagnosis of this parasite requires specialized techniques (e.g. Baermann and Koga agar plate method), but these are rarely employed in epidemiologic studies. We assessed the occurrence of S. stercoralis in a rural part of southern Yunnan province, China, and compared different diagnostic methods. At least two stool samples were obtained from 180 randomly selected individuals, and examined with four diagnostic approaches, including the Koga agar plate and the Baermann technique. Twenty-one individuals were infected with S. stercoralis (prevalence: 11.7%). Males were more often infected than females (18.3% versus 6.1%, p = 0.011). Infections were absent in children below the age of 15 years. The Baermann technique showed a higher sensitivity than the Koga agar plate method, and the examination of multiple stool samples improved the diagnostic performances of both methods. The use of a mathematical model suggested a ‘true’ S. stercoralis prevalence of 16.3%. There is a need to further study the epidemiology of strongyloidiasis in other parts of China, and control measures are required in settings with high prevalences as observed in this area.