Friday, April 18, 2014

Understanding the spatial epidemiology of malaria in Western Uganda

The Bugoye Health Center (BHC) is located in the Kasese District of Western Uganda. This health center functions as the highest level of care for residents of the Bugoye sub-county, serving a rural population of approximately 50,000. The closest higher-level facility, Kilembe Mines Hospital, is located sixty minutes away when traveling by motorcycle. BHC is staffed by clinical officers and nurses from the Ugandan Ministry of Health and provides care at no charge. In addition to the outpatient clinic, there is an inpatient ward of twenty beds and a small laboratory with trained staff capable of performing basic diagnostic tests. As in many other resource-limited settings, the health center suffers from an irregular power and water supply and often faces shortages of key medications.

Entrance to Bugoye Health Center, Level III
Even with these limitations, BHC is always busy. Total reported outpatient attendance was 18,722 in 2013; a number that translates to more than seventy outpatient visits per day. While accurate population statistics are not available, malaria clearly represents the major burden of disease. Like most of Uganda, the climate in Bugoye permits stable, year-round transmission. According to health center reports, there were 7,753 cases of malaria at BHC in 2013. Rapid diagnostic tests (RDTs) have largely replaced light microscopy for the diagnosis of malaria, and are used preferentially given the ease of use and time constraints placed on laboratory staff.
Examining blood smears for malaria parasites in the laboratory

Since their introduction in 2011, nearly 7,000 RDTs have been performed at BHC, two-thirds of which were performed in the last year as the supply became more reliable. Accordingly, the number of parasitologically confirmed cases has increased to 42% in the last six months. While there is room for improvement, the introduction of RDTs has resulted in a marked change from the past, when all febrile patients were presumptively treated for malaria. This approach, while simple, contributed to the over-prescription of anti-malarial drugs and the under-recognition of serious bacterial infections.

Outpatient Clinic, Bugoye Health Center
The RDT positivity rate, which measures the percentage of all RDTs that were positive and is often used as a marker of malaria incidence, was 33% in 2013, with monthly rates as high as 51%. Yet even within this small community, there is significant variation between villages. For example, over the past three months, the RDT positivity rate among patients presenting from the villages of Bugoye, Ndughutu, and Bunyangoni was approximately 30%. Among those presenting from the villages of Muramba and Izinga, the positivity rate was 45% and 68%, respectively.

Looking down on Bugoye from the village of Muramba

Why is the positivity rate in these villages, many of which border each other, so different? Understanding this question is central to my work in Bugoye, and ultimately to developing sustainable malaria control interventions. Given that much of life varies little from village to village, I believe that the difference is best explained by geography. The local terrain ranges from mountain highlands in the west, often reaching altitudes of more than 2,000m near the borders of the Rwenzori National Park, to the densely vegetated wetland areas along the banks of the Sabo and Mubuku Rivers. Many of these “micro-environments” are ideal sites for mosquito breeding, and likely fuel the local variations in malaria incidence. Of course, identifying these high-risk areas, especially in a setting where there are no maps, can be challenging. In my next post, I will describe how we are tackling this issue, drawing on our recent experience in the village of Izinga.

Ross Boyce MD, MSc
PGY-2, Internal Medicine
Global Primary Care Program
Massachusetts General Hospital

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