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[SANTIAGO] The number of Haitians infected with cholera may end up twice as many as the UN is estimating, according to a mathematical model of the epidemic.

Cholera broke out in Haiti in late October last year, in the wake of the earthquake the preceding January, which displaced more than a million people. The UN predicted 400,000 cholera cases in the country within one year of its onset.

But the new model predicts nearly 800,000 cases and more than 11,000 deaths between 1 March and 30 November 2011 if there are no new interventions to curb transmission and treat victims.

Jason Andrews, a research fellow at the Harvard School of Public Health in the United States and co-author of the new study, said that the UN estimate is based on the assumption that the epidemic will affect four per cent of the population.

"It is essentially a guess, based on no data, and ignoring the dynamics of cholera epidemics," he said.

The researchers fed daily incidence data from all Haiti provinces since 31 October 2010 — the outbreak of the epidemic — to 24 January 2011 into a revised model on cholera transmission.

They also simulated the potential impact of clean water, vaccination and greater distribution of antibiotics. The authors concluded that 170,000 cases of cholera and 3,400 deaths would be prevented by applying all three measures.

Reducing consumption of contaminated water by only one per cent each week would prevent 105,000 cases and 1,500 deaths; vaccinating ten per cent of the population would prevent 63,000 cases and 900 deaths; and treating all severe cases and half of moderate cases with antibiotics would prevent 9,000 additional cases and 1,300 deaths.

Andrews told SciDev.Net that the interventions could be achieved. "It would be possible to increase availability of water at that rate if the international community made serious investments [while] improved early case detection will be essential if transmission is to be decreased by the use of antibiotics."

Vaccinating ten per cent of the population with a two-dose vaccine requires two million doses, he added.

But Marcos Espinal, head of health surveillance, disease prevention and control at the Pan American Health Organization (PAHO), defended the UN's approach. He told SciDev.Net that "the model used up to now is consistent with reality. We have seen just over 250,000 people with cholera in six months".

Link to full paper in The Lancet*

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The Lancet doi:10.1016/S0140-6736(11)60273-0

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