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NET BENEFITS

Sunday, 18th of September 2011

• NET BENEFITS

From the editors’ summary: ‘the pooled relative reduction in mortality between 1 month and 5 years old associated with household ITN ownership was 23%.’

Abstract and editors’ summary below; full text, with figures, is at

http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.1001091

Net Benefits: A Multicountry Analysis of Observational Data Examining Associations between Insecticide-Treated Mosquito Nets and Health Outcomes

Stephen Lim and colleagues report findings from a multi-country analysis of household survey data on the association between possession of insecticide-treated mosquito nets and child mortality and parasitemia. Scale-up of net coverage was associated with a substantial reduction in childhood mortality and in parasitemia prevalence.

Stephen S. Lim1*, Nancy Fullman1, Andrew Stokes2, Nirmala Ravishankar3, Felix Masiye4, Chrisher J. L. Murray1, Emmanuela Gakidou1

1 Institute for Health Metrics and Evaluation, University of Washington, Seattle, Washington, United States of America, 2 Population Studies Center, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America, 3 Abt Associates Inc., Bethesda, Maryland, United States of America, 4 Department of Economics, University of Zambia, Lusaka, Zambia

Abstract 

Background

Several sub-Saharan African countries have rapidly scaled up the number of households that own insecticide-treated mosquito nets (ITNs). Although the efficacy of ITNs in trials has been shown, evidence on their impact under routine conditions is limited to a few countries and the extent to which the scale-up of ITNs has improved population health remains uncertain.

Methods and Findings

We used matched logistic regression to assess the individual-level association between household ITN ownership or use in children under 5 years of age and the prevalence of parasitemia among children using six malaria indicator surveys (MIS) and one demographic and health survey. We used Cox proportional hazards models to assess the relationship between ITN household ownership and child mortality using 29 demographic and health surveys. The pooled relative reduction in parasitemia prevalence from random effects meta-analysis associated with household ownership of at least one ITN was 20% (95% confidence interval [CI] 3%–35%; I2 = 73.5%, p<0.01 for I2 value). Sleeping under an ITN was associated with a pooled relative reduction in parasitemia prevalence in children of 24% (95% CI 1%–42%; I2 = 79.5%, p<0.001 for I2 value). Ownership of at least one ITN was associated with a pooled relative reduction in mortality between 1 month and 5 years of age of 23% (95% CI 13–31%; I2 = 25.6%, p>0.05 for I2 value).

Conclusions

Our findings across a number of sub-Saharan African countries were highly consistent with results from previous clinical trials. These findings suggest that the recent scale-up in ITN coverage has likely been accompanied by significant reductions in child mortality and that additional health gains could be achieved with further increases in ITN coverage in populations at risk of malaria.

Please see later in the article for the Editors' Summary

Citation: Lim SS, Fullman N, Stokes A, Ravishankar N, Masiye F, et al. (2011) Net Benefits: A Multicountry Analysis of Observational Data Examining Associations between Insecticide-Treated Mosquito Nets and Health Outcomes. PLoS Med 8(9): e1001091. doi:10.1371/journal.pmed.1001091

Academic Editor: Abdisalan Mohamed Noor, Kenya Medical Research Institute - Wellcome Trust Research Programme, Kenya

Received: January 21, 2011; Accepted: July 21, 2011; Published: September 6, 2011

Copyright: © 2011 Lim et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: The Bill & Melinda Gates Foundation provided support. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Abbreviations: CI, confidence interval; DHS, Demographic and Health Surveys; ITN, insecticide-treated mosquito net; LLIN, long-lasting insecticide-treated mosquito net; MIS, Malaria Indicator Surveys; OR, odds ratio; PSU, primary sampling unit; RCT, randomized controlled trial; RR, relative risk

* E-mail: stevelim@u.washington.edu

Editors' Summary 

Background

Malaria is a major public health problem. Half the world's population is at risk of this parasitic disease, which kills a million people (mainly children living in sub-Saharan Africa) every year. Malaria is transmitted to people through the bites of infected night-flying mosquitoes. Soon after entering the human body, the parasite begins to replicate in red blood cells, bursting out every 2–3 days and infecting more red blood cells. The presence of the parasite in the bloodstream (parasitemia) causes malaria's characteristic fever and can cause fatal organ damage. Malaria can be prevented by controlling the mosquitoes that spread the parasite and by owning and sleeping under insecticide-treated nets (ITNs) to avoid mosquito bites. In trials, ITN use reduced parasitemia in young children by about 13% and deaths among children by about 18%. Consequently, the widespread provision of ITNs is a mainstay of the World Health Organization's efforts to control malaria, and in 2005 the World Health Assembly agreed a target of providing ITNs for 80% of the people at risk of malaria by 2010.

Why Was This Study Done?

Although progress towards this goal has been variable, several sub-Saharan African countries have rapidly scaled up the fraction of households that own ITNs from near zero to more than 60% with the support of international donors. But has this scale-up of ITN coverage been accompanied by improvements in health outcomes similar to those seen in the trials of ITNs? ITNs may not work as well under routine conditions as in trials because of, for example, the use of nets that are no longer impregnated with active insecticide; nets have to be retreated regularly with insecticide to maintain their protection against mosquitoes. Unfortunately, in many countries in sub-Saharan Africa, health information systems are weak and incomplete records of deaths are kept, which makes it impossible to determine the rates of malaria-specific morbidity (illness) and mortality (deaths) accurately. In this study, the researchers use data collected in household surveys to examine the association between ITN ownership in a number of sub-Saharan African countries and two specific outcomes—the proportion of the population with parasitemia, and child mortality.

What Did the Researchers Do and Find?

The researchers used a statistical method to assess the association between household ITN ownership or use in young children and the prevalence of parasitemia among children using data from a set of household surveys. They looked specifically at the relationship between ITN household ownership and child mortality using data from 29 surveys undertaken in 22 sub-Saharan African countries. They then pooled the results of the individual surveys. The pooled relative reduction in parasitemia prevalence among children associated with household ownership of at least one ITN was 20%. That is, averaged out over the countries studied, household ITN ownership was associated with a reduction of around a fifth in the prevalence of parasitemia. The pooled relative reduction of parasitemia prevalence associated with children sleeping under an ITN was 24%. Finally, the pooled relative reduction in mortality between 1 month and 5 years old associated with household ITN ownership was 23%.

What Do These Findings Mean?

These findings suggest that the rapid scale-up in ITN coverage that has occurred in several sub-Saharan African countries has been accompanied by significant reductions in child deaths. Importantly, these findings are highly consistent with those from trials of ITNs. The accuracy of these findings may be affected by some aspects of the study design. For example, because the study uses observational data, it is possible that people who own ITNs share other characteristics that are actually responsible for the reduction in parasitemia prevalence and childhood deaths. Nevertheless, these findings add to the body of evidence that ITNs are effective in routine use. Thus, they support continued efforts to scale-up ITN coverage in sub-Saharan Africa and highlight the importance of maintaining ITN coverage in countries that have already successfully scaled up coverage.