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Mathematical model projects almost double the cases estimated by U.N., supports additional public health measuresCurrent projections regarding the eventual size and extent of the cholera epidemic in Haiti may greatly underestimate the potential number of cases, according to a report that will appear in
The Lancet and has been released online. A mathematical model based on current knowledge about the transmission and course of the diarrheal disease arrives at estimates of new cases through November 2011 that almost double those currently projected by the United Nations. The model also reflects the probable impact of public health measures designed to combat the epidemic.
"Our findings suggest that more resources are needed than may be currently planned," says lead author Jason Andrews, MD, of the Massachusetts General Hospital Division of Infectious Diseases. "The number of cases is currently falling, but this is the natural history of an epidemic, and cholera may continue to exact a significant toll over the next year as it becomes established in Haiti."
Before the devastating earthquake of January 2010, cholera had not been reported in Haiti for more than 100 years; but the aftermath of the earthquake, which largely destroyed the country's already inadequate water and sewer systems, set the stage for the cholera outbreak that began in October. The initial U.N. projection of a probable 200,000 cases during the first year was soon raised to 400,000 cases. But those estimates were based on rough estimates of 2 to 4 percent of the population being infected.
According to Andrews and his co-author Sanjay Basu, MD, University of California San Francisco, the U.N. projections were not based on known patterns of infection and disease progression. Nor did they take into account the asymptomatic nature of some infections, the potential impact of vaccination or treatment, and the immunity that develops in those who recover from the disease. To arrive at more accurate estimates, they devised a mathematical model based on information from previous cholera outbreaks that incorporates current understanding of the disease and also includes data from the first months of the Haitian outbreak. Their model predicted that, without additional intervention, 779,000 new cases and more than 11,000 deaths would result from the epidemic from March through November 2011.