Mapping outbreaks

Joseph Oppong
Associate Professor of Geography
Friday, October 22, 2004

With recent warnings about the worldwide appearance of Severe Acute Respiratory Syndrome, more commonly known as SARS, and Buruli ulcer, a disease caused by skin-eating bacteria, healthcare officials are scrambling to learn more about the spread of infectious diseases.

The emerging field of medical geography is supplying some answers, and University of North Texas medical geographer Joseph Oppong is among researchers leading the way.

Using technology such as geographic information systems and computer models based on satellite and statistical data, Oppong identifies where infectious diseases occur and predicts how they will spread.

"Diseases do not respect political boundaries," he says. "They travel internationally without visas. An outbreak in China or Zimbabwe should concern people in other countries around the world.

"For example, SARS began in Asia and spread to several countries worldwide," he says. "SARS shows us that infectious diseases can put frequent international travelers and their close contacts -- family, friends, co- workers -- at risk."

Oppong says using accurate data to map how a disease is likely to spread ultimately helps to contain it.

"If you know where a disease is most likely to have a severe impact, people in the affected area can be provided with health information and vaccinations or quarantined, if necessary, he says.

Spread factors

To track the path of a disease, Oppong gathers data and programs it into a geographical information system. The GIS produces an electronic geographic map of an outbreak.

"I develop this map by downloading and merging information about the lay of the land and statistics from repositories of information such as the Centers for Disease Control, the World Health Organization and the Texas Department of Health," he says.

Such databank information includes characteristics of the disease, when it arrived at each location and how many people at each site were affected.

Other levels of data include economic indicators, health care policies and practices, and population information according to location. To this, Oppong adds information about social interactions, such as regular meetings where people gather, as possible occasions for an infected person to spread a disease.

"All of these factors can influence the impact of infectious diseases," he says. "For example, outdated, understaffed hospitals and public health facilities may actually contribue to the spread of the disease. High populations in close proximity to animals such as pigs and poultry played a part in the case of SARS."

Oppong says one problem with mapping the spread of SARS is that the disease is new and knowledge about the virus is limited.

"What we know is a critical thing," he says. "We use the information we know about a virus close to the SARS virus, and that's the cold virus or the flu."

According to Oppong, symptoms of SARS are very similar to those of the cold virus, but its mode of transmission differs.

"In addition to the normal means such as respiratory droplets from sneezing and coughing, the SARS virus may be passed through other unknown means. This is a source of concern. For example, according to the World Health Organization, in Hong Kong, feces and urine saturated with the virus may have been a source of spread," he says.

Oppong says the virus may stay outside of the body for many hours, which puts people at greater risk of infection.

During last year's SARS outbreak, Oppong offered updates about the spread of the disease to CNN and other members of the media. Since then, he has been mapping the Buruli ulcer disease.

Skin-eating bacteria

Caused by the bacterium Mycobacterium ulcerans, BU is considered by the World Health Organization to be the third most common mycobacterial infection in humans after tuberculosis and leprosy. The skin-eating disease is prevalent in at least 31 countries in Africa, the Western Pacific, Asia and South America.

The World Health Organization launched the Global Buruli Ulcer Initiative in 1998 in response to the growing spread and impact of the disease. How the disease is transmitted is not understood, but it is known to occur in low-lying wetlands near slow-moving or stagnant bodies of water.

"Researchers are puzzled because they do not know how to prevent this disease and protect the populations at risk," says Dr. Asiedu Kingsley, medical officer responsible for the WHO Global Buruli Ulcer Initiative in Geneva.

"Finding reasons the disease occurs in particular locations and not in others is a serious research question that needs to be answered," he says. "Multidisciplinary approaches to solving the Buruli ulcer puzzle are needed, and that is why the work of medical geographers like Dr. Oppong is very important to the initiative."

As part of this project, Oppong is developing a model for predicting the prevalence of BU in two locations in Africa -- southern Benin and Ghana. He received funding from the WHO to procure satellite data for his efforts.

"This data enables us to identify areas that have a mix of environmental features associated with the presence of Buruli ulcer," Oppong says. "Without actually going to the location, we can use this information to identify areas with high likelihood of Buruli ulcer occurrence."

Kingsley says such information will be useful in targeting control and research efforts.

Tracking tuberculosis

In addition to investigating outbreaks such as BU and SARS worldwide, Oppong studies the spread of infectious diseases within buildings.

"When I learned that SARS spread through faulty seals between sewage and water drains in high-rise apartments in Hong Kong, I decided to explore how diseases such as tuberculosis spread in buildings in the United States," he says.

Primarily a disease of the respiratory system, TB is spread by coughing and sneezing. The bacteria that cause it can attack any part of the body, but they usually target the lungs. After the disease has been released into the air, the risk of infection lasts six hours.

According to the Centers for Disease Control, 5.1 of every 100,000 people in the United States were reported to have TB in 2003.

Oppong looked at the number of TB cases present in different zip code areas in the United States and found an unusually high amount of TB in a homeless shelter and factory in Texas.

He teamed up with UNT computer science professor Armin Mikler and graduate students to create computer simulations of these TB outbreaks.

"With computer analysis, we can design a room, introduce virtual people and have them circulate through a space," Mikler says. "We can also vaccinate our virtual characters and create different scenarios of incubation and infection to understand more about the spread of disease under various conditions."

Oppong says these virtual simulations look similar to a computer game.

"Only in this case it's not a game," he says.

Virtual TB

To build the stage for computer "dress rehearsals' based on actual TB outbreaks, the student teams combined information about homeless shelter residents and factory workers with data about each facility.

The computerized blueprints replicated real-life residents and workers moving around in the interior of the buildings.

Student computer programmers directed the movements of these computer agents and indicated the state of their health with different colors. They programmed the agents to spread the TB bacteria by simulated coughing and sneezing.

The teams also re-created environmental conditions from the shelter and factory and simulated behaviors of the residents and workers. They considered factors such as the settling rate of the bacteria, air flow, heating and cooling systems, architectural elements, social interaction and habits like smoking.

For the people with TB, information was included about the date they were tested, the stage of their disease, their location within the facility and time spent there.

Oppong says that, as expected, the research shows that high foot-traffic areas tend to have a higher concentration of germs. But he adds that the simulations identify where hot spots occur within these areas. Based on their findings, the researchers are examining the role ventilation in buildings plays in the spread of TB.

"Identifying places where TB might pose the greatest threat, whether it is in a building or across a continent, allows us to take measures to contain it," Oppong says.

"Until recently, scientists have not had the technology to adequately predict the spread of infectious diseases. Our new technology gives us tools to create a better map for the future."

UNT News Service Phone Number: (940) 565-2108

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