Intended for healthcare professionals


WHO advises blanket anti-worming treatment for children despite lack of benefit

BMJ 2017; 359 doi: (Published 04 October 2017) Cite this as: BMJ 2017;359:j4589
  1. Nigel Hawkes
  1. London

The World Health Organization has strongly recommended the mass treatment of hundreds of millions of children to eliminate worm infections, while admitting that evidence does not prove that it will do any good.1

A Cochrane review2 published in 2015 by a team at the Liverpool School of Tropical Medicine found no evidence that eliminating intestinal worms by treating all children in an area where worms were endemic improved the children’s average height, weight, or nutritional status. A Campbell review published in 2016 confirmed these findings.3

The WHO guideline does not dispute that conclusion. The panel responsible reviewed 65 trials in 23 low and middle income countries and said that children treated twice a year with anthelmintic medicines in areas where worms were endemic showed no evidence of weight gain, height gain, proportion of stunting, cognitive ability, or mortality when compared with children treated with placebo. The quality of evidence showing no effect was moderate to high.

Paul Garner, of the Liverpool School of Tropical Medicine, who is coordinating editor of the Cochrane Infectious Diseases Group, said, “They [WHO] basically recommend community deworming despite the evidence providing what I believe is reasonably good evidence of no effect. It is sleight of hand to make a strong recommendation based on low quality evidence.”

Dirk Engels, director of WHO’s Neglected Tropical Diseases Department, claimed that a “global evidence based consensus” now shows that periodic, large scale deworming is the best way to reduce suffering caused by intestinal worms.

Antonio Montresor, head of WHO’s deworming programme, said that WHO’s plan was to eliminate the harm caused by worm infections in children by regularly treating at least 75% of the estimated 873 million children in areas where prevalence is high. “Now that the world has agreed standards for deworming, at-risk populations are in a better position to reach this target,” he said.

The panel’s rationale for its recommendation comes from trials showing that children known to be infected did show benefits from deworming. The logical conclusion would be to test children and to identify and treat those infected, but this is more expensive than simply treating all children regardless of whether they are infected.

Garner said, “Obviously, children with worms should be treated. But the argument is whether you embark on deworming every child in a continent to ensure this. And it isn’t cheap—the overall costs are high, when you add it all up.”

He also questioned whether the WHO panel should emphasise weight gain seen in children known to be infected. The Cochrane group, in its assessment of the evidence, did not pool the results for weight gain, because two studies carried out 30 years ago in Kenya showed large effects not seen in more recent trials.

Deworming has long been seen by campaigners as a panacea for health, education, and development problems in poor countries. In 2005 WHO claimed that eliminating worm infections would improve intellectual development and cognitive function and help meet the millennium development goals; but the new guideline does not mention these claims, which were based on a single randomised trial4 whose methods have been contested. A recent reanalysis of the data from that trial did not support its main conclusions.5

But many influential bodies, including the Gates Foundation (which provided financial support for the preparation of the WHO guideline), remain committed to deworming. The STH (soil transmitted helminths) coalition coordinates the activities of 55 partner organisations.

In 2015 STH organised a teleconference to discuss how to maintain momentum for deworming in the face of contrary evidence. The main message, participants were told, was that “Cochrane is useful for some understanding but is not a good tool for policy development.”

Participants were urged not to trash randomised controlled trials, which would make them look “panicky and unscientific.” The message, it concluded, should be that mass drug administration is the most effective and cost efficient way to ensure that infected children are treated.


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