How much evidence do we have that mass deworming of children really has much of an impact?

  • muench
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How much evidence do we have that mass deworming of children really has much of an impact?

I would like to ask anyone who is knowledgeable on the subject of deworming the following question:

How much evidence do we have that mass deworming of children really has much of an impact?

Background to my question:

We know that worm infections (helminthiasis) has an impact on cognitive abilities and thus school performance of children - partly via the malnutrition route. Therefore, it seems obvious that mass deworming of children can counteract that.

However, in the Wikipedia article on helminthiasis, a number of studies are quoted that are showing no such effect:

Although mass dewormings improves the health of an individual, outcomes such as improved cognitive ability, nutritional benefits, physical growth and performance, and learning are still in question.[46] For example:

  • A 2000 review of randomised controlled trials of children showed no special benefits on weight gain and cognitive performance.[47]
  • A 2007 Cochrane analysis found no significant improvements in physical growth and cognitive performance among routinely dewormed children.[48]
  • An independent report in 2007 noted no benefit on cognition and school performance, with an inconclusive effect on weight gain.[49]
  • A 2012 Cochrane review found no benefit on weight, blood improvement (haemoglobin content), cognition and school performance.[50]


(see here: en.wikipedia.org/wiki/Helminthiasis#Mass_deworming_of_children )

See also a discussion we have had on the talk page of the article:
en.wikipedia.org/wiki/Talk:Helminthiasis...edit_about_deworming

Another editor pointed out that:

The topic seems to be still under some debate, pending this review: campbellcollaboration.org/lib/project/204/ . Maybe for now we make clear that there are differing opinions, but give weight to the Cochrane review, since the other side of the debate is based on only one study.


The mentioned review sounds really interesting:

Deworming and Adjuvant Interventions for Improving the Developmental Health and Well-being of Children in Low- and Middle-income Countries: A Systematic Review and Network Meta-analysis

Now here is my hypothesis: Deworming on its own is not showing much effect if it is not coupled with sanitation and hygiene improvements (= the mentioned "adjuvant interventions"?) because the re-infection occurs very quickly in that case.

How long is a deworming pill actually effective for? I assume you take it, it gets rid of the worms you have at that time and then the next day you could get re-infected, right? Or is there a "residual" effect against new infections?

It seems to me that deworming is important but that we could possibly make a case that without also having good sanitation (toilets) and hygiene, it is much less effective. Are there good reference to cite for such a statement?

Any deworming experts out there who can enlighten me?
Thanks in advance.

Regards,
Elisabeth

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  • joeturner
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Re: How much evidence do we have that mass deworming of children really has much of an impact?

Members of SuSanA might be interested to know that there is a new Cochrane Review out today which casts additional doubt on the wider effects claimed of deworming programmes.

Deworming drugs for soil-transmitted intestinal worms in children: effects on nutritional indicators, haemoglobin, and school performance by David C Taylor-Robinson, Nicola Maayan, Karla Soares-Weiser, Sarah Donegan, and Paul Garner

onlinelibrary.wiley.com/doi/10.1002/1465...000371.pub6/abstract

The background of this is that claims have been widely made about the cost-effectiveness of deworming programmes, based largely on a trial from Kenya. The data from this trial has now been reanalysed and has been shown to be subject to bias. See

Re-analysis of health and educational impacts of a school-based deworming programme in western Kenya: a pure replication by Alexander M Aiken1, Calum Davey1, James R Hargreaves and Richard J Hayes

ije.oxfordjournals.org/content/early/2015/07/21/ije.dyv127.full

In a fairly scathing commentary on this reanalysis, the editors of the Cochrane review say:

Critically, according to the Cochrane review which two of us author, there is quite good evidence of no effect for the main biomedical outcomes in deworming, making the broader societal benefits on economic development barely credible.

..what weakens the case of deworming still further is that there is now quite good evidence of no effect for most of the main outcomes (Figure 1), including nutritional status, haemoglobin, cognition and school performance. This is important because without these effects it seems implausible that deworming itself would have an independent effect on school attendance or economic development.

We recommend anyone responsible for public or philanthropic money going to large scale deworming to read these replication studies, the original publication, the authors’ responses to the replication and the 2015 version of the Cochrane review that includes corrections from these replications plus data from five further studies, including the recently published DEVTA study of 2 million children


Replication of influential trial helps international policy by Paul Garner, David Taylor-Robinson and Harshpal Singh Sachdev

ije.oxfordjournals.org/content/early/2015/07/21/ije.dyv131.full
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  • F H Mughal
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Re: How much evidence do we have that mass deworming of children really has much of an impact?

This is what WHO says about worm infections in children and the poor:

“Worms infect more than one third of the world’s population, with the most intense infections in
children and the poor. In the poorest countries, children are likely to be infected from the time they stop breast-feeding, and to be continually infected and re-infected for the rest of their lives. Only rarely does infection have acute consequences for children. Instead, the infection is long-term and chronic, and can negatively affect all aspects of a child’s development: health, nutrition, cognitive development, learning and educational access and achievement.”

www.who.int/intestinal_worms/resources/en/at_a_glance.pdf


The executive summary of the WHO publication: National deworming program: Kenya's experience, reads:

"The national census of Kenya 2008 placed the total number of school age going children at 10,624,380 with 8,661,333 (82%) children currently attending school. A national mass fecal examination of 27,729 children from 395 schools, estimated intestinal parasitic worms infections to be five million (56.8%), and subsequently, a mass school deworming program was initiated. Evidence has shown that improved health status leads to increased productivity, educational performance, life expectancy, savings and investments, and decreased debts and expenditure on health care. Studies in the US have shown that worm infections lower’s literacy levels by 13% and lower’s earnings later in life by 43%. Research in Western Kenya showed that schoolbased mass deworming decrease absenteeism by 25%."
www.who.int/sdhconference/resources/draf...nd_paper22_kenya.pdf


Another publication by Deworm the World, titled: School-based deworming: A planner’s guide to proposal development for national school-based deworming programs, says:

“Over 400 million school-age children worldwide are infected with parasitic worms. These infections harm their health and development, and limit their ability to both access and benefit fully from the education system. In 2001, WHO set the goal of treating 75% of school-age children at risk of infection by 2010. However, by the fall of 2006, only 10% of these children were receiving regular treatment. There is a safe, simple, and cost-effective solution: school-based deworming. It has been shown to reduce absenteeism by 25%, and at less than 50 US cents per child per year, school-based deworming is one of the most cost-effective methods of improving school participation ever rigorously evaluated. In pursuit of achieving the Education for All (EFA) and the Millennium Development Goals (MDGs), Ministries of Education, United Nations agencies, the World Bank, and civil society organizations have made school-based deworming an education policy priority. The overwhelming effects of school-based deworming are a crucial step towards achieving universal global education. If there are any best buys or “silver bullets” to support progress in meeting these goals, then school-based deworming is surely one.”
www.schoolsandhealth.org/.../School%20based%20deworming%20-%20 ..

Is it that there are 2 different perceptions, one for the developed countries, and the other for the poor developing countries, with poor hygiene in rural areas?


F H Mughal

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  • muench
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Re: How much evidence do we have that mass deworming of children really has much of an impact?

Dear Mughal,

I am so glad to see that you are another person interested in the issue of intestinal worms! I was starting to worry that it's only me and Joe because we make most posts on this subject. I hope that more people will pipe up with their views, questions or comments on this topic! To everyone: don't just read, but also please post. :-)

After Joe alerted me to that new "re-analysis" of data a couple of days ago, we had a flurry of tweets on twitter with some worm experts (not from the sanitation sector). They sent us links to their statements.

Joe subsequently updated the Wikipedia page on helminthiasis accordingly to summarise the state of the situation which is great!

So it now reads like this (see en.wikipedia.org/wiki/Helminthiasis#Mass_deworming_of_children ):

++++++++++

Discussions about impacts on school attendance and related parameters [edit source | edit]

Although mass dewormings improves the health of an individual, outcomes such as improved cognitive ability, nutritional benefits, physical growth and performance, and learning are still in question.[48] For example:
  • A 2000 review of randomised controlled trials of children showed no special benefits on weight gain and cognitive performance.[49]
  • A 2007 Cochrane analysis found no significant improvements in physical growth and cognitive performance among routinely dewormed children.[50]
  • An independent report in 2007 noted no benefit on cognition and school performance, with an inconclusive effect on weight gain.[51]
  • A 2012 Cochrane review found no benefit on weight, blood improvement (haemoglobin content), cognition and school performance.[52]
  • An updated 2015 Cochrane review added further doubt about the effects on school attendance due to the reanalysis of the data from a major trial in Kenya which showed it to be subject to bias.[53]
Paul Gardner, the co-ordinating editor of the Cochrane Infectious Diseases Group and the 2015 Cochrane review, wrote in a commentary of the reanalysis of the data from the Kenyan trial "there is quite good evidence of no effect for the main biomedical outcomes in deworming, making the broader societal benefits on economic development barely credible... the belief that deworming will impact substantially on economic development seems delusional when you look at the results of reliable controlled trials."[54]

Organisations running large-scale deworming programmes and other public health experts responded to the 2015 Cochrane review in several statements in July 2015:
  • Evidence Action called the reanalysis flawed and said that the authors had "done their darndest to generate controversy."[55]
  • Berk Ozler at the World Bank criticised the methods used in the reanalysis studies and concluded "if anything, I find the findings of the original study more robust than I did before" and that a "number of unconventional ways of handling the data and conducting the analysis are jointly required to obtain results that are qualitatively different than the original study."[56]
  • The aid agency Giving What We Can said in a statement that they would consider the changes, but criticised the choice of papers considered in the Cochrane review, particularly the omission of one important study which did not meet the criteria for inclusion in the review.[57]
  • Academic and commentator Chris Blattman stated that "both sides exaggerate, but the errors and issues with the replication seem so great that it looks to me more like attention-seeking than dispassionate science."[58]
+++++++++

I am personally still very confused about it all and feel a need for further conversations and discussions! If only we could get more of the health (and "health economics") people to interact with us on the forum, I think that would really help.

Joe: I am wondering if we should think about splitting off the deworming debate into a separate Wikipedia page. There is this page on deworming already: en.wikipedia.org/wiki/Deworming
It's very short though and focusses more on animal deworming.

I am wondering if it would be useful to have a deworming page that is separate for humans - separate from the animals deworming page as the issues are really rather different. Worms in animals are not really related to poverty, for one. Animals don't got to school - another difference.
I have actually had discussions around this already on the talk page of the "deworming" page here:
en.wikipedia.org/wiki/Talk:Deworming

Regards,
Elisabeth

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  • joeturner
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Re: How much evidence do we have that mass deworming of children really has much of an impact?

I am also confused, but I do not think the difference here is between developed and developing countries. It seems to me that the debate is between economists and medical colleagues who want to see proof of the claimed benefits.

As I am neither, and do not have the qualifications to understand the debate about statistics and method, I cannot tell who is making more sense.

My feeling is that claims have been made about the low cost of deworming treatment and wide effects in terms of economics, school attainment etc. I think the medics are asking for proof of these claims, but they are very hard to show. I also wonder how effective mass deworming is and whether children need to be regularly retreated - and whether this affects the total cost.

For me, I think, deworming clearly has a big medical effect on an individual basis. I am not really convinced it is necessary (or possible) to prove community effects to a medical standard - but still believe sanitation is more important than deworming for successfully reducing worm infections sustainably. Whilst deworming might be cheaper, I don't believe this should be done without also considering WASH.
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  • hajo
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Re: How much evidence do we have that mass deworming of children really has much of an impact?

I am interested in this discussion as we are on the way implementing a Fit 4 School activity in Moshi and beside hand-washing (with soap) and tooth brushing, regular mass-deworming is a major intervention.

For me as an engineer, and being neither medic nor economist a possible explanation is:

1 Worm treatment of a single child, which otherwise may suffer from chronic worm infection, improves its health, growth, school attendance, learning aptitude. I guess this can be rightly anticipated as I will not go to school and learn properly when I am sick.

2 Worm treatment does not do harm to not infected children. Also treating infected ones protects non-infected from possibility to get infected.

3 It is more economical to treat ‘all’ children than testing for infection and treating only infected ones.

4 When treating ‘all’ children, the ‘success’ (per child) regarding the above criteria (health, growth, attendance, learning) is smaller, because the study includes an (unknown) number of not infected children, whose development is not affected (positively) by the mass treatment. Such the ‘average’ success on the treated children seems low.

5 This low average success makes ‘opponents’ of mass treatment condemn its application.

6 In my view it seems a quarrel between ‘academics’ each fishing for complements and following. And actors like WB, WHO and UNICEF may have a reason to find justification for them promoting mass de-worming.

And ‘yes’, Joe, as far as I know children need regular re-treatment, because de-worming is the treatment of an infection not an immunisation: to-day you are treated against worms, tomorrow you catch a new one.

Ciao Hajo

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Re: How much evidence do we have that mass deworming of children really has much of an impact?

Thanks Hajo, that is very well explained.

I guess part of a debate might be about whether to treat sick children rather than to treat every child twice a year (or whatever it is). If, as you say, giving the medication to healthy children has no adverse effect, then I can believe there are economies of scale.

On the other hand, if this just becomes a box to tick, then the actual provision per child might be inadequate - for example if there are limited amounts of the medication and this only allows sick children to be treated once, when on average they need to be treated twice - meaning that treating healthy children is affecting the healthcare for the sickest.

It feels like handwashing must be similar. A recent trial found handwashing with soap and nail clipping had a dramatic effect on child illness. However it also found that there needed to be a lot invested (in terms of worker time etc) in regularly visiting children's homes to get the effect. So it is more than just about providing free soap and hygiene tuition to people.

Of course, we know this - I just wonder whether the costs calculated and the benefits accrued consider all of these extra costs. Maybe those who want to give the "greatest benefit" for the least cost look at information put out about handwashing and deworming and just end up delivering a single dose of medication or a limited supply of soap to every child. I am uncomfortable about programmes which try to provide a large number of people with a benefit, because the benefit offered is usually inadequate. I would rather supply a smaller number of people with something which is worth having.

I don't really see how handwashing can be considered without addressing drinking/washing water quality or deworming without considering sanitation.
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  • Marijn Zandee
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Re: How much evidence do we have that mass deworming of children really has much of an impact?

Dear colleagues,

I am not a statistician, so I can also not judge the pure technicalities of the arguments. But here is my take:

First off all, this is not happening in a vacuum, there is a lot of debate within (medical) science about research standards. For example:

www.thelancet.com/pdfs/journals/lancet/P...40-67361560696-1.pdf

Despite the comments made in the article above, doing research at the level of medical science is very hard. This is especially true if you are doing the fieldwork in a developing country. Also, research at this level (controlled randomized trials, double blinding, etc.) is relatively new in development. That there are many studies from the last 10 years which do not meet the quality criteria of a Cochrane review is in my opinion not surprising.

One thing which I do find interesting is that there seems to be a strong disagreement between the medical and economical sciences. This disagreement suggests that in the economic sciences (which I think is the corner from which the introduction of randomized trials in development originated) the standards are less strict than in medical science.

I have no time to read the full Cochrane review article, but would be very happy if someone could help me with the following:

That the review comes to the conclusion that the research into the effect of de-worming does not proof that mass de-worming is useful, I can understand. As mentioned above, I can quite easily accept that many of the trials were flawed in some way. What I do find harder to understand is that the reviewers come to a fairly firm conclusion that mass de-worming in not effective based on the same data. I wonder if this is just because they follow the convention that if you cannot prove that something has an effect you have to accept that it does not, or have they done more testing with the available research data which proves that mass de-worming in not effective?

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Marijn

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Re: How much evidence do we have that mass deworming of children really has much of an impact?

Marijn Zandee wrote: Dear colleagues,

That the review comes to the conclusion that the research into the effect of de-worming does not proof that mass de-worming is useful, I can understand. As mentioned above, I can quite easily accept that many of the trials were flawed in some way. What I do find harder to understand is that the reviewers come to a fairly firm conclusion that mass de-worming in not effective based on the same data. I wonder if this is just because they follow the convention that if you cannot prove that something has an effect you have to accept that it does not, or have they done more testing with the available research data which proves that mass de-worming in not effective?

Regards

Marijn


Hi Marijn, they have looked at published results they have decided are suitable for inclusion in the Cochrane review and have collated the overall message.

If anyone wants to check what I've said below, the article is open-access: onlinelibrary.wiley.com/doi/10.1002/14651858.CD000371.pub6/full

Finding 2 says that the data is too poor to know what the effect on infected children is of a single course of deworming medication in terms of weight, haemoglobin, cognition and physical wellbeing.

Finding 3 says that there is better quality information about the effects of giving a single dose of deworming medication to all children in an area where the helminths are endemic. They say there is "probably" no effect on weight gain or haemoglobin and "may be" little or no effect on cognition. And not enough information to make a judgement about well-being and school attendance.

Which isn't a great surprise if children are rapidly getting reinfected after they have received the medication.

In terms of their main finding, they say that the data is mixed in terms of the effects of multiple doses of medication on all children in endemic areas. They say there may be little or no effect on weight gain (low quality data), probably little effect on height (moderate data), little or no effect on haemoglobin (low quality), probably little effect on cognition (moderate), don't know about cognition or school attendance (v low quality data), probably little effect on school performance (moderate data), little or no effect on death (low quality).

It is hard to see these conclusions and see them saying anything other than that single doses of deworming tablets have little effect both on the individual and on a mass basis. They also seem to be suggesting even multiple doses on a mass basis have little measurable effect over not giving any treatment.

edit: in fact the main conclusion is "Current evidence does not support large public health programmes of deworming in developing countries."
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Re: How much evidence do we have that mass deworming of children really has much of an impact?

Joe wrote:
‘Which isn't a great surprise if children are rapidly getting reinfected after they have received the medication.’

If I look at the pictures on Wikipedia (en.wikipedia.org/wiki/Helminthiasis) provided by Elisabeth, I can imagine that these worms have grown over quite some time and have affected the patients’ condition in multiple ways.

My assumption is that treating children every six months ensures that worms never reach numbers and sizes which can affect their wellbeing. I assume developers of the treatment have looked into the growth and multiplication rates of worms.

That may explain why it is not enough to treat once but good enough to treat every 6 months (in living environments where worm infections are endemic).

ciao Hajo

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Re: How much evidence do we have that mass deworming of children really has much of an impact?

hajo wrote: Joe wrote:

That may explain why it is not enough to treat once but good enough to treat every 6 months (in living environments where worm infections are endemic).

ciao Hajo


I have no idea whether the size of the worms is related to medical complications, but can also imagine that it does. But if this is the case, one would think that a single dose that removed large worms would have a big effect, no?

Also, according to Cochrane, there is either not enough information or little evidence of a positive effect of multiple doses of medication when given on a widespread basis to children in areas where the worms are endemic.

Their rather startling point is that the medication does not seem to have any effect on the individual or the community, although they do not seem to have considered multiple doses on infected individuals.

Elsewhere I read that targeting deworming medication to infected children would cost 6-10 times more than treating all children.
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Re: How much evidence do we have that mass deworming of children really has much of an impact?

Dear Joe,

Thanks for your clarification. What had/has me confused in the Cohrane review is the following conclusion:

Treating children known to have worm infection may have some nutritional benefits for the individual. However, in mass treatment of all children in endemic areas, there is now substantial evidence that this does not improve average nutritional status, haemoglobin, cognition, school performance, or survival.

(my emphasis).

While in the table that summarizes their findings:
onlinelibrary.wiley.com/doi/10.1002/14651858.CD000371.pub6/full
They say the quality of the data is low or moderate. So how do they get to such a strong conclusion, from the data that they consider low/moderate in quality? As I said, this is probably somewhere in the report, but I don't have the time to dig it up.

In general the "worm wars" look pretty nasty to me. I don't really have anything to do with de-worming at the moment so I will leave it for what it is.

For me the conclusion is that de-worming alone is not going to solve the problem. So we need safe toilets as a first crucial step. Further, I still wonder how big transmission rates from animals (walking freely in villages) to humans are.

Regards

Marijn

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