The use of insecticide treated nets by age: implications for universal coverage in Africa

Abstract

Background: 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.

Methods: Recent national household survey data for 18 malaria endemic countries in Africa were assembled to identify 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.

Results: 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 > or =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.

Conclusion: 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.

Figure 1

Graphs of percentage of sample population sleeping under ITN the night before survey, overall and by gender, against the number of persons enumerated in each age category (left) and pie charts of the proportion of projected 2007 population who did not sleep under ITN by age category (right) in: A) group 1: countries where ≥ 20% of the sample population slept under ITN (Kenya, Tanzania, Zambia, Mali); B) group 2: countries where 10-<20% of the sample population slept under ITN (Benin, Senegal, Angola, Djibouti, Sudan); C) group 3 - countries where<10% of the sample population slept under ITN (Rwanda, Uganda, Namibia, Niger, DRC, Zimbabwe, Ethiopia, Guinea, Swaziland). Pink, blue and black lines on the graphs represent the percentage female, male and total sample population sleeping under ITN the night before survey respectively.

Figure 2

Graph showing the prevalence of infection (red line) among individuals of all ages in the Coast province of Kenya prior to scaled ITN delivery [31]and the proportion of the population sleeping under an insecticide treated net (green line) in 2007 after the national free mass campaign of 2006 [32]. The graph illustrates that in Kenya the national ITNs scaling-up strategies have been sub-optimal in terms of targeting the populations aged 5-19 years (shaded grey), the age-group in which pre-intervention parasite prevalence was at its peak.