Mar 17, 2011 (CIDRAP News) US researchers are predicting on the basis of mathematical modeling that Haiti could have close to 800,000 cholera cases and 11,100 deaths this year, more than three times the 250,000 cases counted since the epidemic began last fall.
Writing in The Lancet, the researchers say their prediction is close to double the estimate of 400,000 cases within 1 year that was offered last October by the United Nations Office for the Coordination of Humanitarian Affairs.
But a spokesman for the Pan American Health Organization (PAHO), part of the World Health Organization, a UN agency, cautioned that forecasts based on modeling can be inaccurate.
The researchers, Sanjay Basu, MD, of the University of California, San Francisco (UCSF), and Jason Andrews, MD, of Harvard Medical School, said they developed their model by starting with existing models of cholera transmission and plugging in cholera incidence data for each Haitian province from Oct 31, 2010, through Jan 24.
Using the model, they projected that 779,000 cholera cases and 11,100 deaths could occur in Haiti between Mar 1 and Nov 30 of this year. The 95% confidence intervals are 599,000 to 914,000 cases and 7,300 to 17,400 deaths.
The researchers also used the model to predict the possible effects of improving access to clean water, vaccination, and antibiotic treatment. The model predicted that a 1%-per-week decrease in consumption of contaminated water could prevent 105,000 cases and 1,500 deaths, and that vaccination of 10% of the population could avert 63,000 cases and 900 deaths.
Providing antibiotics to all patients with severe dehydration and half of those with moderate dehydration could prevent 9,000 cases and 1,300 deaths, the report predicts.
Andrews and Basu write that the decline in Haiti's cholera cases since the beginning of this year "is part of the natural course of the epidemic, and should not be interpreted as indicative of successful intervention. Substantially more cases of cholera are expected than official estimates used for resource allocation."
In a UCSF press release, Basu commented, "The epidemic is not likely to be short-term. It is going to be larger than predicted in terms of sheer numbers and will last far longer than the initial projections."
Daniel Epstein, a PAHO information officer in Washington, DC, said today that Haiti's cholera toll as of Mar 10 was 252,640 cases and 4,672 deaths.
In commenting on the Lancet report, he told CIDRAP News, "We have to be cautious because modeling does not necessarily reflect what's seen on the ground. Modeling estimates can be inaccurate. The model used up to now is consistent with reality. We have seen just over 250,000 people with cholera in 6 months."
Epstein said PAHO's priority in Haiti is to save lives by rapidly providing cholera patients with oral rehydration therapy and using intravenous therapy in more severe cases.
"We need to reconstruct water and sanitation systems for the cholera epidemic to go away completely," he added. "It's a long-term process, and cholera may be around for a number of years yet."
Andrews JR, Basu S. Transmission dynamics and control of cholera in Haiti: an epidemic model. Lancet 2011 Mar 16 (early online publication) [Abstract]
Mar 15 UCSF press release
Related Lancet editorial