A cross-sectional analysis of ITN and IRS coverage in Namibia in 2013

Malaria Journal Allcock et al. Malar J (2018) 17:264 https://doi.org/10.1186/s12936-018-2417-z Open Access RESEARCH A cross‑sectional analysis of ITN and IRS coverage in Namibia in 2013 Sophie H. Allcock1,2, Elizabeth H. Young1,2 and Manjinder S. Sandhu1,2* Abstract Background: Achieving vector control targets is a key step towards malaria elimination. Because of variations in reporting of progress towards vector control targets in 2013, the coverage of these vector control interventions in Namibia was assessed. Methods: Data on 9846 households, representing 41,314 people, collected in the 2013 nationally-representative Namibia Demographic and Health Survey were used to explore the coverage of two vector control methods: indoor residual spraying (IRS) and insecticide-treated nets (ITNs). Regional data on Plasmodium falciparum parasite rate in those aged 2–10 years (PfPR2–10), obtained from the Malaria Atlas Project, were used to provide information on malaria transmission intensity. Poisson regression analyses were carried out exploring the relationship between household interventions and PfPR2–10, with fully adjusted models adjusting for wealth and residence type and accounting for regional and enumeration area clustering. Additionally, the coverage as a function of government intervention zones was explored and models were compared using log-likelihood ratio tests. Results: Intervention coverage was greatest in the highest transmission areas (PfPR2–10 ≥ 5%), but was still below target levels of 95% coverage in these regions, with 27.6% of households covered by IRS, 32.3% with an ITN and 49.0% with at least one intervention (ITN and/or IRS). In fully adjusted models, PfPR2–10 ≥ 5% was strongly associated with IRS (RR 14.54; 95% CI 5.56–38.02; p < 0.001), ITN ownership (RR 5.70; 95% CI 2.84–11.45; p < 0.001) and ITN and/or IRS coverage (RR 5.32; 95% CI 3.09–9.16; p < 0.001). Conclusions: The prevalence of IRS and ITN interventions in 2013 did not reflect the Namibian government intervention targets. As such, there is a need to include quantitative monitoring of such interventions to reliably inform intervention strategies for malaria elimination in Namibia. Keywords: Malaria, Indoor residual spraying, Insecticide-treated nets, Vector control, Namibia Background Malaria is a global public health concern, causing approximately 438,000 deaths, worldwide, in 2015 [1]. The World Health Organization (WHO) Africa Region experiences a disproportionately high burden of malaria, with 88% of global cases in 2015 occurring in the region [1]. Namibia is one of eight sub-Saharan African countries aiming to eliminate malaria, and intends to eliminate by 2020. *Correspondence: 2 Wellcome Sanger Institute, Hinxton, Cambridgeshire CB10 1SA, UK Full list of author information is available at the end of the article Interventions for malaria control and elimination include indoor residual spraying (IRS), insecticidetreated nets (ITNs) and long-lasting insecticide-treated nets (LLINs). These are effective tools for reducing the adult mosquito population density and longevity, and are therefore fundamental for interrupting transmission [2]. ITNs and LLINs have successfully reduced the risk of infection in a number of settings [3–5], with up to 90% reductions in malaria transmission recorded following ITN implementation in some high-transmission settings [6]. High coverage of ITNs and IRS can both result in community-level protection [7, 8], highlighting the importance of high coverage and uptake of these interventions. There is also evidence to suggest that using IRS © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Allcock et al. Malar J (2018) 17:264 and ITNs in combination is more effective at reducing the vector population and interrupting transmission than ITNs alone [9, 10]. Malaria transmission in Namibia is heterogeneous. In 2013, it was estimated that 67% of Namibia’s population were living in the highest transmission areas [11]. Prevalence of malaria is highest in the northern regions that border Angola [12]. Namibia has experienced fluctuations in malaria incidence with reported cases rising from 4911 in 2013 [11] to 15,915 in 2014 [1], with two outbreaks occurring in 2016 and 2017 [13–16]. Importantly, between 2000 and 2015, Namibia’s overall malaria incidence and mortality rates increased by over 20% [17], highlighting the need for an effective elimination programme. Namibia’s 2010–2016 Malaria Strategic Plan (MSP) aimed to achieve at least 95% coverage with a combination of vector control interventions in all malaria endemic areas and identified transmission foci by 2013 [12]. However, the 2013 Namibia Demographic and Health Survey (DHS), a nationally-representative survey that collected data on IRS and ITN coverage, reported that only 24% of households had at least one ITN, and just 16% of households had received IRS during the previous 12 months [18]. By contrast, a governmental report indicated that IRS was successfully completed in the eight malaria regions, with 93% coverage of targeted households achieved by the end of January 2013 [19]. To understand these discordant findings, a detailed analysis of ITN and IRS coverage was conducted as a function of DHS data, malaria transmission patterns and government intervention zones across Namibia in 2013. Methods Ethical considerations Data used in these analyses were available through the DHS Programme [20]. Ethical review and approval for procedures and questionnaires for standard DHS surveys is provided by the ICF Institutional Review Board (IRB). Country-specific DHS survey protocols are reviewed by the ICF IRB and typically by an IRB in the host country. Verbal consent is obtained from the participant and a signature is provided by the interviewer to acknowledge that this event has taken place. Displaced geographical coordinates were obtained following approval from the DHS Programme. Data were securely stored separately from individual and household data. Data sources The DHS programme conducts standardized, nationallyrepresentative surveys in over 90 countries worldwide, collecting data pertaining to the broad themes of fertility, family planning, maternal and child health, human Page 2 of 13 immunodeficiency virus (HIV), malaria, and nutrition [21]. The methods of the 2013 Namibia DHS are detailed elsewhere [18]. In summary, the survey used a two-stage stratified clu (...truncated)