On Location
Place matters—that’s epidemiology 101.
Until recently, gathering data and charting it on maps meant going door to door to survey families and then plotting the findings on paper. It was a tedious process at best and mostly two-dimensional. Data mapping might show, for instance, which households within a community had been affected by a certain disease or problem and where the condition was most prominent, but would most likely reveal nothing about relevant climate or social demographics in that particular area.
Today’s tools for epidemiological mapping offer much more, not only in detail but also in efficiency and ease. As a result, geographic information systems (GIS) are changing the way epidemiologists approach the entire concept of place as a component of public health. In some cases, GIS mapping requires little more than basic computer skills and a global positioning system (GPS)-enabled cell phone. More complicated applications require extensive training but also offer multidimensional analyses, including environmental factors like elevation and climate. Either way, for scientists looking to demonstrate the importance of place in public health, the options have far outstripped the tools of 20 years ago.
“Some of the biggest advances made have been in supporting technologies, like remote sensing of the environment using satellites and finding out, for instance, the soil moisture in Zambia today versus two days ago. Those are things you certainly couldn’t have gotten in the past,” says epidemiologist Greg Glass, PhD, a professor in the Department of Molecular Microbiology and Immunology.
“One of the limitations we often cite is that we're unclear about the effects of the environment on individuals and communities. GIS has brought a population-based approach that looks at the relationship between people and place.”—Debra Furr-Holden
Such environmental factors often correlate directly with epidemiological concerns. Take, for instance, the relationship between rainfall and the prevalence of malaria-carrying mosquitoes. Knowing which areas are more vulnerable to malaria outbreaks, says Glass, allows aid workers to predict where assistance—such as bed net distribution—is most needed.
In earlier work, Glass used geographic mapping to predict an increased risk of hantavirus in certain areas, based on increased precipitation and vegetation. More vegetation means a booming population of the rodents that carry hantavirus.
The resulting images vary depending on circumstances, sometimes appearing as heat maps—brightly colored maps resembling those used by meteorologists, with the highest risk areas showing a bright red. A map of a predicted malaria outbreak, on the other hand, might illustrate which areas of Bangladesh are both highly populated and highly vulnerable to malaria, encasing those areas in concentric circles.
Shannon Doocy, PhD, with the Center for Refugee and Disaster Response, often uses GIS to study natural disasters and affected communities.
She and her colleagues also use GIS information to analyze approaching storms, in hopes of anticipating which areas are most vulnerable. “If you can have a good understanding of where a hurricane is likely to hit and flooding is likely to occur,” she says, “you can plan humanitarian assistance efforts with a better understanding of what to anticipate post-disaster.”
One example, she says, was Cyclone Nargis in Burma (Myanmar). “After that, we created a GIS model that estimated the affected population,” explains Doocy, an assistant professor in International Health. “There was an area where a lot of aid groups were being restricted, and there wasn’t a lot of access to information or good estimates of the affected population. The UN was able to use our maps and population estimates to inform their emergency response.”
But determining the significance of place has historically proved more complicated when studying less concrete issues, such as the role that one’s social environment might play in substance abuse. Here too, however, GIS is proving valuable, says Debra Furr-Holden, PhD, an associate professor in Mental Health.
Much of Furr-Holden’s research centers on the epidemiology of drug and alcohol abuse in Baltimore City. Using handheld GPS devices, she says, researchers can venture into the community to collect data about where they’re finding indications of violence, alcohol use, tobacco and drugs, as well as potentially influencing factors such as poverty or crime rates. Meanwhile, the GPS automatically records the location where researchers are collecting data.
One successful project occurred a few years ago, when Furr-Holden and her colleagues were studying whether the proximity of liquor stores and bars to schools influenced the rate of underage drinking. Not only did they find an increase in alcohol use in children, they linked it to poor academic and substance abuse outcomes.
Further still, researchers found that several establishments were violating a Baltimore law barring alcohol sales within 300 feet of a church or school. “Using that data, we were able to work with the city to identify which outlets were violating the law,” Furr-Holden says. “They were actually able to get some of those nonconforming outlets closed because we were able to make a strong case from the public health perspective that there would be health improvements if they took this on.”
That, she says, was made possible through GIS.
“One of the limitations we often cite in public health is that we’re unclear about the effects of the environment on individuals and communities has brought to public health a population-based approach that looks at the relationship between people and place. We now have the tools and capacity to look at the broader impact of the environment on individuals and communities and their health and health behaviors.”