Predicting the unmet need for biologically targeted coverage of insecticide-treated nets in Kenya

Abstract

In some countries the biological targeting of universal malaria prevention may offer optimal impact on disease and significant cost-savings compared with approaches that presume universal risk. Spatially defined data on coverage of treated nets from recent national household surveys in Kenya were used within a Bayesian geostatistical framework to predict treated net coverage nationally. When combined with the distributions of malaria risk and population an estimated 8.1 million people were not protected with treated nets in 2010 in biologically defined priority areas. After adjusting for the proportion of nets in use that were not long lasting, an estimated 5.5 to 6.3 million long-lasting treated nets would be required to achieve universal coverage in 2010 in Kenya in at-risk areas compared with 16.4 to 18.1 million nets if not restricted to areas of greatest malaria risk. In Kenya, this evidence-based approach could save the national program at least 55 million US dollars.

Figure 1.

The distribution of the community survey locations showing the reported insecticide-treated nets (ITN) coverage among all ages from the MIS 2007 (N = 199); PSI-TRaC 2007 (N = 280); and the FSD 2009 (N = 646) surveys.

Figure 2.

(A) 1 × 1 km spatial resolution Kenya map of the distribution of predicted posterior mean insecticide-treated nets (ITN) coverage among all ages in 2009; (B) 1 × 1 km map of the number of standard deviations from the posterior mean ITN coverage in 2009. Large values of standard deviation from the mean indicate wider confidence intervals and high uncertainty around the predictions at each 1 × 1 km grid.

Figure 3.

A 100 × 100 m spatial resolution three-dimensional map of population distribution in Kenya 2010 against: (A) malaria risk presented as modeled age-standardized Plasmodium falciparum parasite prevalence (PfPR_2–10) of < 1% (pink) and ≥ 1% (dark red); (B) the predicted posterior mean insecticide-treated nets (ITN) coverage. The darker the color the higher the predicted ITN coverage; and (C) areas of priority for the distribution of long-lasting insecticidal nets (LLIN) defined as those where the posterior mean malaria risk was ≥ 1% PfPR_2–10 and population density was ≥ 1 person per km² shown in green. Areas shown in pink are those where PfPR_2–10 was < 1% or population was < 1 person per km² and were regarded as not priority for LLIN distribution because of the low overall biological risk of infections. The three-dimensional maps were generated using Arcsence 9.3 (ESRI Inc., New York).