Impact of an insecticide treated net programme on the prevalence of parasitaemia and anaemia in children under two years of age in the Kilombero Valley Tanzania.

Referee Opinion

General Comments

This paper has tackled a very important question in Malaria control. Can what is demonstrated in controlled conditions be maintained when the intervention is extended to the community where many other factors as well as less control will operate.

This paper has not clearly answered the question put forward in the title. Nevertheless it has answered an important question for malaria control. This paper clearly demonstrates that using bed nets in a community setting will have an advantage in children at risk for malaria. It will decrease the anaemia and the parasitaemia when bed nets are used. However the advantage that is seen with Insecticide Treated Nets (ITN) over the use of untreated nets is not very clear here. In addition there are many other factors associated with the ability to buy and own bed nets which will have favourable effects on decreasing the anaemia and parasitaemia in the children. The paper has correctly tried to include these factors in its analysis but it may be difficult to isolate the impact of ITN in these situations. The statement in the Results section under "Health impact of ITN’s" demonstrates the problem – "Untreated nets had a protective efficacy (PE) of 51% (95% CI: 0 to 76%), while for treated nets the PE was 63% (95% CI:38 to 77%) when compared with children without nets". Therefore the major protective effect appears to be the nets itself. Considering the fact that this was a project to extend from a controlled situation to the community, the fact they were able to extend the nets to the community is significant by itself.

Specific comments

In the Introduction in the last sentence of the first paragraph, there is a statement that most children at the risk of severe anaemia live beyond the reach of hospitals. This statement only has unpublished data for support. I would think that a better reference for this should be given or the statement omitted. In the fourth paragraph of the Introduction, the first statement is that there is large-scale implementation of ITN’ s underway in a number of African countries. Again this is an unsupported statement and references would be needed.

In the Methods section it is mentioned that ITNs were sold at 5 US dollars. It would be useful to get some idea of the local income to assess how expensive or not the ITNs were. In the design it is only in the last of third surveys, that households were examined for nets. It is not explained as why this was not done in the first and second. Perhaps this was an improvement which was realised midway through the study. If so, this should be specifically stated. It might also be useful to mention whether the slides for malaria parasite were read "blind" or the microscopist knew whether the slide had been taken from a child who had, or did not have a bed net. It is also specified that the treatment of nets was classified on the basis of respondents answers as either "ever treated" or "not treated". This is a reasonable measure as it would have been difficult to do more refined data collection. However this crude assessment again goes to the central problem of whether insecticide treatment has been important or not. Thus the intrinsic limitations present in the study, makes one hesitant to accept the conclusion of importance of insecticide treated nets.

In the Results section in the subsection on net ownership and use, the last paragraph which describes observation of sleeping places is confusing. It does not appear that the figures add up and this paragraph should be clarified.

In Procedure the first sentence begins as "Selected children …………". This should be "The selected children …"; omitting this word gives a very different meaning to the sentence, which, I do not think is what the authors intended.

To conclude, comments as requested in the BMJ letter

Research question – This was clearly defined but may not have been appropriately answered although a part of the problem was the intrinsic limitation of such an observational study.

Overall design of the study – The design was adequate but could have been better with inspection of the observation of sleeping places done from the beginning. Participants studied were adequately described and the conditions were defined well.

Methods – Adequately described and ethically adequate.

Results – Here, there is quite a lot of data and at times the reader gets lost in all the figures. Perhaps the authors should emphasise the important results more.

Interpretation and Conclusions – Here the focus on insecticide treated nets does not appear warranted. Nets by themselves appear to have been the major factor that decreased the parasitaemia and anaemia. Insecticide treatment could have had a small and additive effect.

References – Appear adequate and up to date. However reference 14 is given in slightly greater detail in an already published article.