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Those tackling the epidemic are struggling to keep pace with an escalating crisis.
As cholera rampages through Haiti, some epidemiologists are warning that the country could face more than half a million cases over the coming year. Yet tracking and treating the disease is proving increasingly difficult as civil unrest grips the county.
Roughly 20,000 clinical cases, and 1,100 deaths, have officially been reported since the outbreak was first detected on 21 October in the Artibonite region of Haiti - figures likely to be underestimates, say epidemiologists, given the many additional cases in the wider community. "It's spreading like wildfire," says Andrew Camilli, a cholera researcher at Tufts University School of Medicine in Boston, Massachusetts (see 'Epidemic proportions').
As the current Haitian population has never been exposed to cholera, they lack any immunity to the disease, which makes the toll even greater. Vaccination might have helped, but it has never been tested during a large cholera outbreak and was not an option in Haiti because of the vaccine's scarcity and the logistical difficulties in getting it to people in time (see 'Would cholera vaccines have helped in Haiti?').
Cholera is caused by the bacterium Vibrio cholerae, transmitted through contaminated water supplies or by direct contact with infective faecal material. Haiti already lacked clean water and basic sanitation, and conditions have deteriorated further following January's huge earthquake (see Nature 467, 1018-1019; 2010) and Hurricane Tomas in early November.
Some 80% of symptomatic cholera cases are mild or moderate, but 20% cause severe dehydration from watery diarrhoea that can kill within hours if untreated. Until the 1970s, when oral rehydration therapy was widely introduced, death rates during outbreaks often exceeded 50%. But cholera is eminently treatable if patients are promptly rehydrated, and public-health responses to cholera epidemics typically reduce mortality rates to below 1%.
Experts think that conditions in Haiti are resulting in far higher death rates than this....