Rain, temperature may predict cholera months in advance

A study performed by scientists from the International Vaccine Institute in Seoul, Korea, has discovered that rain and temperature fluctuations in at-risk areas may predict epidemics of cholera months in advance.

With recent cholera outbreaks in Cameroon and Haiti, a study such as this that can anticipate outbreaks may allow public health authorities in areas where cholera is more common to move to intervene with measures such as vaccines that are less effective when an epidemic is in full swing.

"Cholera outbreaks are occurring with increasing frequency and severity," Peter J. Hotez, the president of the American Society of Tropical Medicine and Hygiene, said. "This research is an example of an innovative approach that if used in conjunction with other preventive measures could significantly reduce the needless suffering and deaths of thousands of people."

In the study, scientists analyzed several years of disease and environmental data from the cholera-endemic areas of Zanzibar, Tanzania, and found that a mere one degree Celsius increase in the average minimum monthly temperature was a warning sign that cholera cases would double within four months. A 200 millimeter increase in monthly rainfall totals indicated a slightly lower but still substantial increase in cases within two months.

"Our work validates the notion that rainfall and temperature increases are often precursors to cholera outbreaks in vulnerable areas," Rita Reyburn, a research associate at IVI and the study's lead author, said. "We are getting very close to developing a reliable forecasting system that would monitor temperatures and rainfall patterns to trigger pre-emptive measures—like mobilizing public health teams or emergency vaccination efforts—to prepare for an outbreak before it arrives."

The researchers said that their study is an advance in developing a cholera outbreak forecasting system because there are multiple environmental factors known to contribute to infections of cholera and it has thus far been difficult to single out which ones are the most integral to model.

"Predicting outbreaks is crucial because right now public health officials only know for sure that an outbreak is underway when people start getting sick, which is too late for things like vaccines to have maximum effectiveness," Mohammad Ali, a senior scientist at IVI, said. "If we wait for clinical signs of the disease to emerge, that means a large portion of the population is already carrying the cholera bacteria, they just are not yet exhibiting clinical symptoms."