Soil-transmitted helminths
For STH infection, WHO recommends the use of cumulative prevalence – the prevalence of infection with at least one STH species – for deciding whether or not to implement targeted mass treatment and, if so, for determining the frequency of treatment. WHO recommend that, when the cumulative prevalence of STH is:
- ≥50% - treatment targeted to all school-age children twice each year
- 20-49% - treatment targeted to all school-age children once each year
Schistosomiasis
A similar classification can be used for targeting treatment of schistosomiasis. When the prevalence of schistosome infection is:
- ≥50% - annual treatment of all school-age children
- 10-49% - treatment once every 2 years of school-age children
- <10% - targeted treatment of all school-age children twice during primary schooling (at entry and on leaving)
The appropriate treatment strategy can be determined by simple and low-cost survey techniques that identify whether the school is in an area with significant risk of infection.
Lymphatic filariasis
WHO recommends mass drug administration of entire districts where prevalence exceeds 1%, as determined on the basis of mapping using immunochromatographic tests (ICT).