Investigation of the epidemiology of Malaria in the Engela health district of the Ohangwena region in Northern Namibia
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Date
2016
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University of Namibia
Abstract
Namibia has seen a decline in reported malaria cases of up to 97.4% between 2001 and 2011. The country was nominated as one of 8 countries in Southern Africa (E8) ready to move from the control phase to the elimination phase by 2020. However, interventions that were successful in bringing down malaria cases during the control phase may no longer be appropriate now that malaria transmission patterns have changed. Gaps in knowledge about infection risk factors at low malaria transmission, such as cross border movement and the possibility of localized malaria hotspots where residual malaria may still persist create an obstacle to eliminating malaria. An effective surveillance system may contribute to zero local transmission of malaria in Namibia. Currently, passive surveillance of malaria cases is conducted; however, this can be complimented by reactive case detection (RACD) which focuses on detection of additional malaria cases within the community. An RACD study was piloted in the Engela Health District of the Ohangwena region from December 2012 to July 2014. All individuals with fever testing malaria positive by rapid diagnostic test (RDT) from the 17 clinics in the district were recruited into the study and visited at their homesteads. Consenting individuals living in the case household were screened for malaria by RDT and interviewed to ascertain the presence of possible malaria risk factors; four surrounding households were also selected and recruited into the study. For the control arm, households in the enumeration area where malaria was not reported were recruited as controls for the study and their four surrounding households were also recruited. During the study period, a total of 190 confirmed malaria cases were reported from Engela Health District of which 70 (36.5%) were local individuals residing within the district and 8 (4.2%) were asymptomatic cases discovered during RACD. From the remaining cases, 47 (24.7%) were of Angolan nationals who do not reside within the district but only crossed the border seeking medical treatment and 65 (35.2%) were regarded as untraceable cases due to various factors such as lack of or false information given at the health facility. Risk mapping and geo-locating of confirmed local cases and asymptomatic cases revealed pockets of infection in the northern regions of the district parallel to areas where clustering occurred. Increased probability of malaria infection in these areas was estimated at a mean of 2.2%, with a range of 0.04% - 28.3%. Travel, insecticide residual spraying (IRS) and mosquito net coverage were among the top significant contributors to increased risk of malaria infection. Travel was found to be more common among male individuals from case neighbourhoods with the most frequent destination being Angola. Net coverage was 4% lower in case neighbourhoods compared to control neighbourhoods with statistical analysis showing that risk of infection was much lower among net users as opposed to non-users (OR=0.89, 95% CI: 0.45-1.74). From control neighbourhoods, 67.4% of sleeping structures were not sprayed compared to 72.2% of sleeping structures from case neighbourhoods. With the presence of eaves in 70.2% of unsprayed case neighbourhood sleeping structures, risk of exposure to mosquitoes was increased due to ease of entry. Despite the need to improve the quality of information collected from patients at health facilities, RACD is a plausible method for monitoring malaria elimination and identifying asymptomatic reservoirs in the district. With RACD, the chance of finding an asymptomatic case was 8 times more likely to occur in the index household where a malaria case was initially reported while also making it possible to identify potential hotspots of infection. Risk factors associated with the likelihood of being a confirmed case were travel, IRS and net coverage which highlighted possible reasons towards continued malaria transmission. However, the perception of low malaria risk due to significant decrease in malaria transmission results in the need to re-educate communities on the importance of continued practice and implementation of vector control strategies such as IRS and net coverage and use in order to bring transmission down to zero.
Description
A thesis submitted in fulfilment of the requirements for the Degree of Master of Science
Keywords
Epidemiology, Malaria, Engela