Global Prevalence of Threadworm Determined

Worldwide data on infection rates of threadworm have been collected from a number of sources, analyzed using spatial statistics, and presented on a global map.

The threadworm, also called Strongyloides stercoralis, is a soil-transmitted worm endemic worldwide, yet more prevalent in hot and humid climates as well as resource poor countries with inadequate sanitary conditions.

Parasitologists at the Swiss Tropical and Public Health Institute (Basel, Switzerland) performed a meta-analysis to obtain country-specific prevalence estimates and to compare disease odds ratios in different risk groups taking into account the sensitivities of the diagnostic methods applied. A total of 354 studies from 78 countries were included for the prevalence calculations, 62.4% were community-based studies, 34.2% were hospital-based studies and 11.0% were studies on refugees and immigrants. Included were articles published between January 1989 and October 2011.

Some studies reported on tropical West and East Africa. However, infection rate data is scarce for Sahelian, Central, and Southern Africa. Most of the available studies used low sensitivity diagnostic methods. Adequate diagnostic techniques, such as the Baermann funnel technique and Koga Agar plate culture, were employed in only 19.0% of the studies in African countries. A large amount of information is available for Brazil, where 43 studies were undertaken. Most investigations were conducted in communities rather than in hospitals. For the USA, 22 studies were identified and almost two thirds of them focused on refugees and immigrants.

Studies on refugees and immigrants were mostly conducted, with a few exceptions, in developed countries. Most found high infection rates in immigrants and refugees, reaching prevalence rates of up to 75%. Infection rates varied substantially depending on the refugees' country of origin. In Canada, where they used high sensitivity diagnostic tools, they found a prevalence rate of 11.8% in Vietnamese refugees compared to 76.6% in Cambodian refugees. In most cases, the infection remains undiagnosed and untreated.

The authors recommend that to further increase diagnostic sensitivity, more than one stool sample should be examined from the same individual over consecutive days. It is necessary to conduct further studies using highly sensitivity diagnostic methods, coprologically the Koga Agar plate culture or the Baermann or the enzyme-linked immunoassay (ELISA) in serology, to achieve a more comprehensive and detailed picture of the global prevalence of S. stercoralis. The study was publishes on July 11, 2013, in the journal Public Library of Science Neglected Tropical Diseases.

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Swiss Tropical and Public Health Institute