Mar. 16, 2011 A new study conducted at the University of California, San Francisco (UCSF) and Harvard Medical School predicts that the cholera epidemic in Haiti this year will be far worse than United Nations' projections, which had estimated 400,000 cases of the diarrheal disease over the course of the epidemic.
The study, to be published March 16 in the journal Lancet, is predicting instead that there could be nearly twice that number -- perhaps 779,000 cases of cholera -- between March and November this year alone. U.N. projections are key because they determine how resources are allocated.
"The epidemic is not likely to be short-term," said UCSF medical resident Sanjay Basu, MD, who conducted the study with Jason Andrews, MD, a former UCSF resident who is now a fellow at the Massachusetts General Hospital and Harvard Medical School. "It is going to be larger than predicted in terms of sheer numbers and will last far longer than the initial projections."
In addition to revising the predicted scope of the epidemic, Andrews and Basu modeled the effect of three public health interventions that authorities might use to curtail the epidemic: providing clean water, vaccinating some of the population and prescribing antibiotics more widely.
Expanded access to antibiotics is the most controversial of the three, said Basu, because of the high cost. However, the results of the analysis suggest that antibiotic treatment of cholera could save thousands of lives this year in Haiti.
An Epidemic by the Numbers
Before last year's devastating earthquake in Haiti, no cases of cholera had been seen on the island for more than 100 years. But in the wake of the earthquake, the disease has reemerged as a major epidemic.
Caused by a few related strains of bacteria that spread from person-to-person through contaminated food and water, cholera causes acute diarrhea and can be deadly if untreated. Treatment is simple, for the most part, requiring health care workers to rehydrate patients with salty liquids.
Cholera is completely preventable where modern sanitation systems provide clean water for everyone. The disease thrives, however, where clean water is not available. Cholera is often found in poor and underdeveloped parts of the world, in war-torn countries, and in areas devastated by natural disasters -- places where there are displaced populations, large groups of people living in overcrowded camps, and nonexistent or overtaxed sanitation and sewer systems. These are exactly the conditions that have existed in Haiti following the earthquake last year.
In the three months between October and December of last year, about 150,000 people in Haiti contracted cholera, and about 3,500 died.
In October of last year, the U.N. first projected that some 200,000 people would eventually become infected, and then two weeks later, they doubled this projection to 400,000.
According to Basu, however, the U.N. numbers did not incorporate existing disease trends or take into account major factors like where water was contaminated, how the disease is transmitted or even human immunity to cholera. Instead, they were based on a simple assumption that the disease would infect a set portion (2 to 4 percent) of Haiti's population of 10 million, Basu said.
Using data from Haiti's Ministry of Health and other sources, Andrews and Basu made a more sophisticated model of the spread of disease in several Haitian provinces. The results surprised even them, according to Basu, leading to predictions of 779,000 cases and about 11,100 fatalities in the next eight months.
Their study also examines the effect of making clean water more available and interventions involving vaccines or antibiotics. They estimate that a mere 1 percent reduction in the number of people forced to drink contaminated water would avert more than 100,000 cases of cholera this year and prevent some 1,500 deaths. Vaccinating about 10 percent of the population would spare about 900 lives. The work also predicts that extending the use of antibiotics more widely would prevent 9,000 cases of cholera and 1,300 deaths.
Antibiotics, Basu said, do not just protect "the person who receives them but also reduces their infectiousness and helps reduce transmission."
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- Jason R Andrews and Sanjay Basu. Transmission dynamics and control of cholera in Haiti: an epidemic model. The Lancet, March 16, 2011 DOI: 10.1016/S0140-6736(11)60273-0
Note: If no author is given, the source is cited instead.