Spatial epidemiology on @NPR @MorningEdition: #Malaria and gold mining

Thursday, May 11, 2017

I've unexpectedly found myself in hog heaven since moving to the Maryland side of DC for a new position at the beginning of this month. I'm staying with a friend while I look for my own place and, while I have a much longer commute than I am used to, I am enjoying all 40 minutes of it because I am spending all of them listening to WAMU, the DC-area NPR station out of American University. I've always liked NPR, not only because they provide (I feel) balanced coverage of major news items, but also because they feature so many interesting stories that wouldn't normally get much press, including engaging pieces on public health and human rights.

Case in point: Yesterday's Morning Edition featured a story on how illegal gold mining has been linked to malaria in Colombia. The segment featured an interview with Sandra Rozo, an economist with USC's Marshall School of Business, whose recent work has focused on providing an evidence base for qualitative data suggesting a link between alluvial gold mining and higher incidence of malaria:
As illegal gold mining is mainly performed in open sky mines that are commonly located inside or close to water surfaces where large pits are dug, it is plausible to conceive that these pits are later filled with water, which would make them ideal breed sites for Anopheles mosquito larva. Because these mines do not follow any protocols or rules and are not registered with local authorities, it is likely that illegal miners have limited knowledge of the need for or methods of malaria prevention. They are likely to leave the pits open and do not take any measures to protect themselves against malaria. Finally, illegal gold miners are also a population that sustains high migration rates, which could also help to propagate the parasite incidence to other areas. Due to data limitations, however, at present, the existing evidence has been concentrated on qualitative studies or on documenting correlations between malaria incidence and gold exploitation.
As she points out in her paper, however, there are a number of other factors that could contribute to the correlation without the relationship being causal per se - hence the value of supporting quantitative epidemiological analysis. Rozo is not the first to explore this from an epidemiological perspective, either. This paper by Castellanos et al finds a strong correlation between gold production rates and malaria cases using malaria surveillance data and government data on legal mining activities. One major limitation, though, was that they could examine correlations to legal mining activities - that is, mining operations that are registered with, and regulated by, the government. The paper also notes that between the two types of mining (traditional alluvial vs. the more modern "open sky"), the "open sky" technique is less regulated and more likely to be performed illegally.

Rozo's analysis is interesting for a couple of reasons. She combines satellite data identifying mining operations with geographic data on geochemical anomalies of gold and matches that to malaria surveillance data to determine the relationship between gold mining activity and malaria incidence. She also controls for several potential confounders, including poverty levels, presence of government and health institutions, climactic factors, and chronic disease.

This is the type of analytical application that makes spatial epidemiology so exciting and demonstrates how epidemiology can be used to build or strengthen the case for policy change to benefit public health. It also spotlights why political and economic forces that we don't typically think of as explicitly health related are still very much relevant to public health researchers and policy makers. Less than a month before Rozo's paper was posted, the New York Times ran a story on how malaria has come back with a vengeance in Venezuela since the economic crisis. As many professionals had turned to gold mining to survive, they were repeatedly getting sick with malaria - and taking it back to the cities with them.

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