Disease Forecasters Look to the Sky for Predictions

PLEASANT HILL, CA - JUNE 29: Contra Costa County Mosquito and Vector Control District technician David Wexler inspects a carbon dioxide trap for mosquitos on June 29, 2012 in Pleasant Hill, California. As reports of mosquitoes with West Nile virus are increasing across the country and several people have been confirmed to be infected by the potentially dangerous disease, the Contra Costa County Mosquito and Vector Control District is testing mosquito larvae found in standing water throughout the county and is using mosquito fish and BVA Larvacide oils to eradicate the pest. (Photo by Justin Sullivan/Getty Images) (2012 Getty Images)

You may not know whether it will rain next month, but at least you’ll be able to tell whether flu season is still in.

Health scientists are trying to move forward with “disease forecasting” as they increasingly include whether data in their attempts to predict outbreaks.

In one recent study, two scientists reported they could predict — more than seven weeks in advance — when flu season was going to peak in New York City. Theirs was just the latest in a growing wave of computer models that factor in rainfall, temperature or other weather conditions to forecast disease.

At the same time, experts note that outbreaks are influenced as much, or more, by human behavior and other factors as by the weather. Some argue weather-based outbreak predictions still have a long way to go. And when government health officials warned in early December that flu season seemed to be off to an early start, they said there was no evidence it was driven by the weather.

This disease-forecasting concept is not new: Scientists have been working on mathematical models to predict outbreaks for decades and have long factored in the weather. They have known, for example, that temperature and rainfall affect the breeding of mosquitoes that carry malaria, West Nile virus and other dangerous diseases.

Recent improvements in weather-tracking have helped, including satellite technology and more sophisticated computer data processing.

In the United States, researchers at Johns Hopkins University and the University of New Mexico tried to predict outbreaks of hantavirus in the late 1990s. They used rain and snow data and other information to study patterns of plant growth that attract rodents. People catch the disease from the droppings of infected rodents.

Some diseases are hard to forecast, such as West Nile virus. Last year, the U.S. suffered one of its worst years since the virus arrived in 1999. There were more than 2,600 serious illnesses and nearly 240 deaths.

Some think flu lends itself to outbreak forecasting — there's already a predictability to the annual winter flu season. But that's been tricky, too.

Seasonal flu reports come from doctors' offices, but those show the disease when it's already spreading. Some researchers have studied tweets on Twitter and searches on Google, but their work has offered a jump of only a week or two on traditional methods.

In the study of New York City flu cases published last month in the Proceedings of the National Academy of Sciences, the authors said they could forecast, by up to seven weeks, the peak of flu season.

They designed a model based on weather and flu data from past years, 2003-09. In part, their design was based on earlier studies that found flu virus spreads better when the air is dry and turns colder. They made calculations based on humidity readings and on Google Flu Trends, which tracks how many people are searching each day for information on flu-related topics (often because they're beginning to feel ill).

Despite the optimism by some, Dr. Edward Ryan, a Harvard University professor of immunology and infectious diseases, is cautious about weather-based prediction models.

"I'm not sure any of them are ready for prime time," he said.

Based on reporting by the Associated Press.