Deworming for Soil-Transmitted Helminths

The World Health Organization (WHO) recommends fighting soil-transmitted helminth infections by giving all at-risk population groups periodic anthelminthic treatment with one of two safe, effective, and low-cost medicines: albendazole (400 mg) or mebendazole (500 mg) in areas with endemic infection levels (WHO 2002). At-risk groups include preschool-age children, starting at 12 months of age; school-age children and women of reproductive age, particularly pregnant women after the first trimester; and lactating women.

According to WHO, treatment should be given once a year in areas with an infection burden higher than 20 percent and twice a year in areas with prevalence higher than 50 percent (WHO 2016). WHO prevalence categories are used to recommend the frequency of deworming; prevalence is based on school-age children because this population group has available data most often, but treatment applies to all populations (see Table 3).

In many countries where soil-transmitted helminths are endemic, administration of anthelmintic medication is combined with other routine health events: Child Health Days, school health programs, and others. Anthelmintic medication is also administered as part of routine primary health care and routine antenatal care for high-risk groups. The medicines, widely administered to everyone in the high-risk groups, can be given without prior diagnosis and, often, by non-medical personnel.

Table 3: Prevalence Levels for Treatment of Soil-Transmitted Helminth Infection

Prevalence of Any Soil-Transmitted Helminth Infection Among School-Age Children Treatment
≥50% Blanket treatment: 2 times per year for school-age children.
Also treat:
  • Preschool children
  • Women of childbearing age, including pregnant women in 2nd and 3rd trimester and lactating women
  • Adults at high risk in certain occupations (e.g., tea pickers and miners)
≥20% and <50% Blanket treatment once per year for school-age children.
Also, treat—
  • Preschool children
  • Women of childbearing age, including pregnant women in 2nd and 3rd trimester and lactating women
  • Adults at high risk in certain occupations (e.g. tea pickers and miners)

Source: Crompton and WHO 2006

Measurement and data sources

Population-based surveys typically report the percentage of children 6–59 months who were given deworming medication in the six months preceding the survey, as well as the percentage of women with a live birth in the two to five years before the survey who were given deworming medication during their most recent pregnancy. In post-event coverage surveys, coverage is the percentage of the eligible population who received deworming medication during the last campaign. These surveys usually take place within a few weeks of the campaign, and interviewers will show the participants the medications to ensure accurate recall.

Surveys that collect information related to deworming coverage include—

  • Demographic and Health Surveys
  • Multiple Indicator Cluster Surveys
  • National Micronutrient Surveys
  • post-event coverage surveys
  • Knowledge, Practice, and Coverage Surveys
  • other research or evaluation activities.

In addition, health monitoring information systems may include coverage estimates of deworming activities, both from mass treatment events, as well as routine treatment. In the case of campaign-based distribution, these data often come from tally sheets completed at the time of mass drug administration, which are compared against the total target population to obtain coverage estimates.

Methodological issues

  • Generally, tally sheets and other administrative data may overestimate deworming coverage compared to post-event coverage survey data, so it is preferable to use post-event coverage data.
  • Recall bias in these routine population-based surveys may result in lower coverage estimates compared to post-event surveys.
  • Consider the regularity of deworming campaigns, as well as the timing of data collection in relation to a deworming campaign. Discrepancies may be noted between different data sources, based on whether information was collected prior to or following a deworming campaign. In other words, coverage estimates from Demographic and Health Surveys, Multiple Indicator Cluster Surveys, or National Micronutrient Surveys may be affected by the time interval between the survey and the mass antihelminthic treatment, especially when estimates are compared between years.
  • While WHO recommends anthelminthic treatment for children starting at 12 months, many population-based surveys collect information about deworming coverage in children younger than 12 months. It is best to exclude these younger children in the overall assessment of deworming coverage, especially if a country policy is aligned with WHO recommendations of starting deworming at 12 months.
  • While looking for information on this topic, remember that most data on deworming refers to both treatment for schistosomiasis and soil-transmitted helminths.
  • Understanding antenatal care visits is helpful for interpreting data regarding deworming for pregnant women. Many countries, however, do not consistently record or report these data, complicating efforts to explain coverage of antenatal care services (Dwivedi et al. 2014).