Cholera, according to the Mayo Clinic, is a bacterial disease that spreads through contaminated water or food. Symptoms of cholera can include nausea, vomiting, severe diarrhea, dehydration and even death if left untreated. There were more than 130,000 reported cases of cholera worldwide in 2016, according to the World Health Organization, but estimates of the true number of cholera cases are much higher – between 1.4 million to 4 million cases annually.
"In the countries less developed with infrastructure that is not the equivalent, let's say, of Europe or the United States or Canada, then, the population that has to rely on river water or pond water is at risk for cholera," microbiologist Rita Colwell said in a new video from NASA's Goddard Space Flight Center. She is a microbiologist and professor at the University of Maryland, College Park, and at Johns Hopkins University Bloomberg School of Public Health. [Photos: NASA's Rain-Tracking GPM Satellite Mission in Pictures]
According to NASA, cholera outbreaks come in two types: endemic (or seasonal), or an epidemic that happens suddenly. If the use of drinking water and its availability change after a natural disaster, human behavior will also change as people seek out water. But it is difficult to predict the risk of cholera because little information is available on pathogen abundance in local water systems as well as on larger trends in weather and climate.
Researchers focused on Haiti, which suffered a massive cholera outbreak in 2010 after a difficult year of natural disasters. A devastating earthquake and an aftershock hit Haiti in January 2010, followed by the hottest summer in generations. A cholera outbreak occurred in October of the same year, just weeks before Hurricane Tomas grazed the island and unleashed heavy rains.
"The data that we were able to pull together showed that in 2010 it was the hottest summer in 50 years. And then, as if that weren't enough, there was a hurricane that skirted the island, but it dumped the heaviest rainfall in 50 years," added Colwell, who is the former director of the National Science Foundation.
Antarpreet Jutla, a hydrologist at West Virginia University, was part of a team that created an algorithm to determine the risk of cholera. This gave the researchers "the first clues" on the cholera outbreak in Haiti after the earthquake, he said in the NASA video. Then, Hurricane Matthew swept through Haiti in 2016.
By that time, the GPM mission had been in space for two years, tracking global snowfall and precipitation. Jutla's team reused their cholera prediction algorithm, adding improved satellite data from the GPM mission, to see where cholera might occur. The model includes factors such as monthly air temperature, population density, precipitation, the severity of the natural disaster and availability of infrastructure for water, sanitation and hygiene.
"We were able to, in real time, predict the risk of cholera infection in human population at least four weeks in advance. We did the same thing for Yemen," Jutla said. "We knew there was a mass movement of human population due to civil unrest in that part of the world, and then we had very heavy precipitation. And then we immediately started monitoring conditions. And that basically converged to give us a risk on where and when this disease will lock in on human population."
The researchers said they hope to improve the spatial scale of the model as they include more data sets. "I think we can predict and prevent [cholera], and I'd like to see that happen very quickly, in the next three to five years, and I'd like to see the satellite system to be part of the regular public health tools so that we can do prediction as well as the tracking of epidemics that's done traditionally now," Colwell said.