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 recommends the following for different percentages of cumulative prevalence:
- ≥50% - treatment targeted to all school-aged children twice each year
- 20-49% - treatment targeted to all school-aged children once each year
Schistosomiasis
A similar classification can be used for targeting treatment of schistosomiasis. Treatment depends on the percentage of schistosome infection prevalence:
- ≥50% - annual treatment of all school-aged children
- 10-49% - treatment once every 2 years of school-aged children
- <10% - targeted treatment of all school-aged 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
For treatment of lymphatic filariasis the WHO recommends mass drug administration (MDA) to the entire population in an endemic geographical region where prevalence exceeds 1%. This is determined using the WHO-recommended mapping strategy, which measures the presence of LF antigens in blood samples collected in the selected implementation units (IU), the defined mapping and treatment regions.
The presence of LF antigens in the blood, or antigenemia, is determined by examining 50 -100 individuals over the age of 15 in two locations in each IU using a rapid diagnostic test, immunochromatographic card (ICT). If the prevalence exceeds 1% in at least one of the pre-selected locations, the entire IU is considered endemic to LF and will require a minimum five rounds of MDA.
