Mathematical model predicted when cholera epidemic would peak in war-torn Yemen

A recently developed mathematical model accurately forecasted that a large-scale cholera outbreak would peak in war-torn Yemen by early July 2017, triggering more than 750,000 cases.

The model was developed by researchers at Hokkaido University in Sapporo, Japan.

While various amounts of epidemiological research using mathematical models have been conducted throughout the world, most were undertaken in order to contain epidemics and how to best distribute limited public health resources. However, no study has been conducted using mathematical models to provide updated forecasts for the virus.

Using weekly data on suspected cases and fatalities between April 16 and July 1 compiled by the World Health Organization (WHO), Hokkaido researchers utilized time lags between the onset of the disease and the reporting of the disease in its mathematical model to examine the epidemic curve that was updated on a weekly basis.

By studying death rates, the researchers were able to discover a new method that corrects ascertainment bias, which refers to a tendency to report cholera cases after many new suspected cases appear rather than the initial phase of the outbreak.

From its newly-organized dataset, the research team estimated that the cumulative cholera cases at the end of the epidemic would be 790,778 on its logistic model and 767,029 the Richards model, a generalized logistics curve. Additionally, the team was able to forecast that the epidemic curve would peak on the 26th week of 2017 and then drop in subsequent weeks. The drop in suspected cases was noted in WHO data by mid-August 2017.

“Our model succeeded in excluding two biases for the first time and the resulting forecast has been proven reliable so far,” Hiroshi Nishiura, professor in the Department of Hygiene at Hokkaido University, said. “Real-time forecasting could assist enhancing situation awareness about the ongoing epidemic communication between experts and citizens while avoiding excessive pessimism, in addition to crafting future measures against cholera.”

Caused by the bacterium Vibrio cholerae, cholera is an infection of the small intestine that presents symptoms such as watery diarrhea, vomiting, dehydration and muscle cramps. According to research published in the Lancet, approximately 28,000 people worldwide succumb to the disease’s lethal effects each year.