Evaluating Effectiveness of Mass and Continuous Long-lasting Insecticidal Net Distributions Over Time in Madagascar: A Sentinel Surveillance Based Epidemiological Study

Abstract

Background: The reduction of global malaria burden over the past 15 years is much attributed to the expansion of mass distribution campaigns (MDCs) of long-lasting insecticidal nets (LLIN). In Madagascar, two LUN MDCs were implemented and one district also benefited from a community-based continuous distribution (CB-CD). Malaria incidence dropped but eventually rebounded after a decade.

Methods: Data from a sentinel surveillance network over the 2009-2015 period was analyzed. Alerts were defined as w eekly number o f malaria cases exceeding the 90th percentile value for three consecutive weeks. Statistical analyses assessed the temporal relationship between LLIN MDCs and (i) number of malaria cases and (ii) malaria alerts detected, and (iii) the effect of a combination of MDCs and a CB-CD in Toamasina District.

Findings: Analyses showed an increase of 13.6 points and 21.4 points in the percentile value of weekly malaria cases during the second and the third year following the MDC of LLINs respectively. The percentage of alert-free sentinel sites was 98.2% during the first year after LLIN MDC, 56.7% during the second year and 31.5% during the third year. The number of weekly malaria cases decreased by 14% during the CB-CD in Toamasina District. In contrast, sites without continuous distribution had a 12% increase of malaria cases.

Interpretation: These findings support the malaria-preventive effectiveness of MDCs in Madagascar but highlight their limited duration when not followed by continuous distribution. The resulting policy implications are crucial to sustain reductions in malaria burden in high transmission settings.

Keywords: LLINs effectiveness; Madagascar; Malaria; Sentinel surveillance.

Fig. 1

Location of the health centers participating in the sentinel surveillance system in Madagascar and surrounding climate.

Fig. 2

Mass LLIN campaign distribution held in 2012–2013 in Madagascar. UNICEF: United Nations Children's Fund, PMI: President's Malaria Initiative, NMCP/GF: National Malaria Control Program.

Fig. 3

Percentile value of malaria cases vs LLIN.

Fig. 4

Kaplan Meier of site week probability of alert. Censored observations are denoted by red crosses and numbered in brackets. The number of sites remaining at risk at different points is numbered in orange. The 95-confidence interval is denoted by dots.