The use of insecticide treated nets by age: implications for universal coverage in Africa
© Noor et al; licensee BioMed Central Ltd. 2009
Received: 22 June 2009
Accepted: 1 October 2009
Published: 1 October 2009
The scaling of malaria control to achieve universal coverage requires a better understanding of the population sub-groups that are least protected and provide barriers to interrupted transmission. Here we examine the age pattern of use of insecticide treated nets (ITNs) in Africa in relation to biological vulnerabilities and the implications for future prospects for universal coverage.
Recent national household survey data for 18 malaria endemic countries in Africa were assembled to indentify information on use of ITNs by age and sex. Age-structured medium variant projected population estimates for the mid-point year of the earliest and most recent national surveys were derived to compute the population by age protected by ITNs.
All surveys were undertaken between 2005 and 2009, either as demographic health surveys (n = 12) or malaria indicator surveys (n = 6). Countries were categorized into three ITN use groups: <10%; 10 to <20%; and ≥20% and projected population estimates for the mid-point year of 2007 were computed. In general, the pattern of overall ITNs use with age was similar by country and across the three country groups with ITNs use initially high among children <5 years of age, sharply declining among the population aged 5-19 years, before rising again across the ages 20-44 years and finally decreasing gradually in older ages. For all groups of countries, the highest proportion of the population not protected by ITNs (38% - 42%) was among those aged 5-19 years.
In malaria-endemic Africa, school-aged children are the least protected with ITNs but represent the greatest reservoir of infections. With increasing school enrollment rates, school-delivery of ITNs should be considered as an approach to reach universal ITNs coverage and improve the likelihood of impacting upon parasite transmission.
The slow progress toward the target set by African heads of state in Abuja in 2001 of 60% coverage of insecticide-treated nets (ITNs) among vulnerable children and pregnant women  has, in recent years, shown promising signs of changing with rapid scaling-up of ITNs coverage in many African countries . However the Abuja target, and the Millennium Develop Goal 6 (80% coverage of children and pregnant women) , do not account for scaling ITN to achieve high coverage of all population segments necessary to reduce malaria transmission and protect communities. The scaling of ITNs demands a shift from prioritizing vulnerable populations to protecting everyone, including the most vulnerable, by achieving high coverage and community-wide use of ITNs. ITNs at high coverage levels impact vector population survival and abundance, where those not sleeping under an ITN will benefit and a mass-effect is achieved. The latter has been observed during trials of ITNs during the 1990's [4–8]. Theoretical models strongly support the likely benefit of levels of coverage beyond those most vulnerable to the clinical burden posed by Plasmodium falciparum [9, 10]. Underpinning these models is the fact that it is estimated that 80% of human-to-mosquito transmission originates from human hosts older than 5 years of age, with P. falciparum prevalence, under stable malaria transmission, rising during early childhood, peaking in older children and falling through adolescence and adulthood .
There are now extensive temporal data on ITNs coverage across Africa since 2000 generated as part of national household cluster sample surveys [2, 12, 13]. These data have been used to examine progress toward coverage of ITNs among children under five years of age and pregnant women [2, 12, 14] or determinants of use [15, 16]. Inevitably survey tools and indicators were developed around international targets established 10 years ago and thus most data focus on coverage of ITNs among the vulnerable groups or provide some indication of ownership among households. Notable is the paucity of data presented on coverage and use by age and sex across the entire surveyed community.
Following recent calls for universal coverage of ITNs and other vector control strategies , and given the biological basis for the target, we have analyzed datasets from those recent national surveys that describe coverage by age and sex among all members of a household.
Summary of national households surveys with data on ITN use among all age-groups in African countries where national surveys reported information on all ages: countries are ranked from highest to lowest based on the proportion of individuals of all ages who slept under an ITN the night prior to survey.
Number of clusters sampled for survey
Number of households samples for survey
Number of persons seen during survey
Number of ITN owned by the sampled households
% of household with at least two ITN
% of children <5 years old sleeping under ITN the night before survey
% of persons of all ages sleeping under ITN the night before survey
A summary of ITN use among individuals of ages < 5 years; 5-19 years; 20-44 years; and ≥45 years and the estimated number of persons (millions) in each age group NOT protected with ITN in 2007: countries are ranked from highest to lowest based on the proportion of individuals of all ages who slept under an ITN the night prior to survey.
Millions children < 5 years in 2007 (% sleeping under ITN)
Millions children < 5 years of age NOT sleeping under ITN in 2007
Millions children 5-19 years in 2007 (% sleeping under ITN)
Millions children 5-19 years of age NOT sleeping under ITN in 2007
Millions of persons 20-44 years in 2007 (% sleeping under ITN)
Millions of persons 20-44 years of age NOT sleeping under ITN in 2007
Millions of person ≥ 45 years of age in 2007 (% not sleeping under ITN)
Millions of persons ≥ 45 years of age NOT sleeping under ITN in 2007
Among the 18 national, household surveys analyzed across a range of overall ITNs coverage settings a common pattern of reported ITNs use emerges with highest coverage among children aged less than five years, dropping to lowest levels of coverage among children and adolescents aged 5-19 years and rising again through adulthood before a drop among the oldest household members (Figures 1a-1c). Similar differentials of ITNs use between young children and older age groups have been reported during studies in Tanzania [22–24], South Central Somalia , Ethiopia  and Nigeria . The two most plausible and linked explanations for these observed patterns are that first most ITNs delivery programmes have historically focused on ensuring young children have access to nets either through routine clinic visits, attendance at regular vaccination visits, their mothers while pregnant or nets delivered as part of mass-catch-up immunization campaigns that target young children . Consequently this age group would be expected, following recent efforts to scale coverage, to show the highest reported ITNs use. However, secondly this will be linked to the way people share sleeping structures in a household, where nursing and younger children will sleep with their mothers and/or both parents, who will most often be between 20-44 years of age. Conversely older children will sleep on separate beds or mats elsewhere in the household.
Operations research in Africa show that the pre-existing infrastructure of schools can cost-effectively deliver simple health interventions, including deworming and micronutrients, as well as feeding programmes . In areas of high enrollment, where the majority of non-enrolled school age children have at least one sibling attending school and few differentials in enrollment by socio-economic and health status exists , school health programmes are likely to be extremely equitable. Even in areas of low enrollment, non-enrolled children can still benefit from school health programmes: experience in several African countries demonstrates that many out-of-school children will take advantage of services, such as deworming, provided through schools . Such features of school-based programmes provide a potentially equitable and cost-effective framework for malaria control . Already, drug-based approaches to the prevention of malaria infection and anaemia in this target population are being considered again [35–38] after popular chemoprophylaxis strategies for school children in Africa during the 1950s and 1960's [39–41]. Given the poor coverage of current ITN programmes as a means to prevent infection among school aged children, pragmatic trials or operational investigations of the impact of ITNs delivered to children attending school should be compared to the provision, separately or in combination, with drugs used for intermittent presumptive treatment. In addition there is need to increase effective communication to households to encourage optimum usage of ITNs to address the widespread problem of households often using only a proportion of the nets they own while some household members remain unprotected . Effective use of these reserve nets will also reduce redundancy in ITNs distributions by national programmes.
In conclusion, the study shows that in malaria endemic African countries, school-age children are the least protected with ITNs. School-delivery of ITNs, therefore, should be considered as an approach to reach universal coverage and improve the likelihood of impacting upon malaria parasite transmission. As most sub-Saharan African countries move towards universal coverage of ITNs it becomes important that national survey data can be used to redefine optimal approaches to this new strategy. Therefore data on ITN use must be collected for all household members and not, as is the case with the MICs surveys and some DHS surveys, for those only under the age of five years and pregnant women.
Demographic and Health Surveys
Malaria Indicator Surveys
Multiple Indicators Cluster Surveys
Insecticide Treated Nets
Millennium Development Goals.
Victor Alegana is thanked for his help in data manipulation from the various websites. We thank Drs Dave Smith and Simon Hay for their comments on earlier versions of the manuscript. This paper is published with the permission of the director KEMRI.
AMN is supported by the Wellcome Trust as a Research Training Fellow (#081829). SB is supported by the Wellcome Trust as a Career Development Fellow (#081673). RWS is supported by the Wellcome Trust as Principal Research Fellow (#079080). This work forms part of the output of the Malaria Atlas Project (MAP, http://www.map.ox.ac.uk), principally funded by the Wellcome Trust, UK. We also acknowledge support from the Kenya Medical Research Institute. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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