Location, location, location: environmental factors better predict malaria-positive individuals during reactive case detection than index case demographics in Southern Province, Zambia

Abstract

BackgroundDecreasing malaria transmission leads to increasing heterogeneity with increased risk in both hot spots (locations) and hot pops (certain demographics). In Southern Province, Zambia, reactive case detection has formed a part of malaria surveillance and elimination efforts since 2011. Various factors may be associated with finding malaria infections during case investigations, including the demographics of the incident case and environmental characteristics of the location of the incident case.MethodsCommunity health worker registries were used to determine what factors were associated with finding a malaria infection during reactive case detection.ResultsLocation was a more powerful predictor of finding malaria infections during case investigations than the demographics of the incident case. After accounting for environmental characteristics, no demographics around the incident case were associated with finding malaria infections during case investigations. Various time-invariant measures of the environment, such as median enhanced vegetation index, the topographic position index, the convergence index, and the topographical wetness index, were all associated as expected with increased probability of finding a malaria infection during case investigations.ConclusionsThese results suggest that targeting the locations highly at risk of malaria transmission is of importance in elimination settings.

The use of spatial and genetic tools to assess Plasmodium falciparum transmission in Lusaka, Zambia between 2011 and 2015

“…The results found herein suggest that there is vectoral capacity in the periphery to facilitate malaria transmission if malaria parasites are present or imported. Malaria control programmes aiming for elimination may be more successful when focusing on locations of human settlements where sufficient habitat enables malaria transmission [56].…”

Improving the efficiency of reactive case detection for malaria elimination in southern Zambia: A cross-sectional study

“…Environmental risk factors were associated with the probability of finding households with parasitemic residents using RCD as demonstrated in other studies in Zambia. 13 In the low transmission setting of Choma District, Zambia, identifying streams located near index households to guide and direct screening of other homes has the potential to improve RCD and affect transmission by identifying households with asymptomatic infections. These findings are in line with a previous study conducted within the same study area in 2008 where it was shown that households within 1.98 km from a third-order stream were 2.8 (95% CI: 1.2 -6.9) times more likely to have an RDT positive resident than those within 6.0 km from the same stream.…”

“…10,12 Running head: Improving efficiency of reactive case detection Residual transmission in "hot spots" is driven by many local environmental factors such as vegetation and availability of aquatic habitats that determine vector density and heterogeneity. 13 For example, Anopheles larval sites contract and cluster around permanent aquatic habitats during the dry season, and expand during the wet season. 14 Various topographical features can also predict incident cases.…”

“…14 Various topographical features can also predict incident cases. 13 To increase efforts towards elimination, RCD may be improved by including environmental risk factors into the screening process, leveraging the heterogeneous nature of malaria transmission as a function of environmental features to guide asymptomatic case detection. 13 The Government of Zambia launched their RCD strategy in 2011 to enhance malaria surveillance and engage health systems at the community level to identify and treat individuals infected with P. falciparum who did not seek care or had minimal or no symptoms.…”

“…13 To increase efforts towards elimination, RCD may be improved by including environmental risk factors into the screening process, leveraging the heterogeneous nature of malaria transmission as a function of environmental features to guide asymptomatic case detection. 13 The Government of Zambia launched their RCD strategy in 2011 to enhance malaria surveillance and engage health systems at the community level to identify and treat individuals infected with P. falciparum who did not seek care or had minimal or no symptoms. 15,16,17 This RCD strategy is part of the National Malaria Elimination Strategic Plan (NMESP) to eliminate malaria in Zambia by 2021 and is employed in communities where parasite prevalence is approximately 1% and ten or fewer cases are passively detected at health facilities.…”