Source: Science 332(6031), 776-777, May 13, 2011.
HAITI'S CHOLERA OUTBREAK
Cholera Linked to U.N. Forces, But Questions Remain
by Martin Enserink
They came to the island with the best of intentions—only to sow disease and death.
An eagerly awaited report from an independent panel leaves little doubt that United Nations peacekeeping forces from Nepal inadvertently introduced cholera to Haiti last fall, triggering an epidemic that has killed almost 5000 and whose end is not yet in sight. The four-member committee, which presented its findings to U.N. Secretary-General Ban Ki-moon in New York City on 3 May, dispatches with the theory that Vibrio cholerae had been lurking in local waters and emerged as a result of favorable ecological or environmental circumstances.
Although the study finds fault with the sanitation at three camps of the United Nations Stabilization Mission in Haiti (MINUSTAH), it is careful not to apportion blame; it also says there is no evidence that anyone within the camps ever suffered from cholera. The entire catastrophe may have started with a single carrier: an infected person who wasn't sick himself but shed the bacteria in his stool, says the panel's chair, Alejandro Cravioto, who heads the International Centre for Diarrhoeal Disease Research, Bangladesh, in Dhaka.
This puts the panel's report starkly at odds with another study by French epidemiologist Renaud Piarroux that was published online last weekend by the journal Emerging Infectious Diseases (EID). Based on data gathered in Haiti early in the epidemic, Piarroux concludes that a Nepalese camp near the town of Mirebalais, in Haiti's Centre department, had a major outbreak of cholera among its men and dumped up to 1000 liters of contaminated feces into local waters, despite telling the world all was fine.
The U.N. panel reviewed a series of genetic studies, some not yet published, which strongly suggested that the V. cholerae strain wreaking havoc in Haiti originated in South Asia and was released in Haiti from a single point. A weeklong investigation on the ground in Haiti convinced the group that the outbreak started in Mirebalais and in a matter of days spread along the Artibonite, Haiti's biggest river, which is used widely for collecting drinking water, bathing, washing clothes, playing, and irrigation.
The Artibonite delta saw a wave of thousands of cases in the first few days, followed by a sharp drop. Only a massive, one-time release of contaminated feces racing down the river could explain that pattern, he writes.
A back-of-the-envelope calculation that takes into account the number of bacteria one needs to ingest to contract a serious case of cholera, the water volume of the river, and other factors leads Piarroux to conclude that more than 100 trillion V. cholerae microbes may have been released—which means that dozens or even hundreds of soldiers were sick. “What happened in this river is something I have never seen in all of my experience with cholera,” Piarroux says.
Cravioto says he has no reason to doubt MINUSTAH's claim that it had no diarrhea cases at the camp. The medical records were silent, he says, and “we didn't see any pages that were torn out.”
Suspicions of a U.N. link to the epidemic have incited protests and violence in Haiti, and the panel does not fan those flames. It says that the outbreak “was not the fault of, or deliberate action of, a group or individual,” and that the introduction would never have evolved into disaster without what Lantagne calls a “perfect storm” of other factors, including Haiti's poor infrastructure and the salinity of the Artibonite delta, which favors V. cholerae's growth.
Nevertheless, it proposes a series of measures to prevent such introductions in the future. U.N. installations around the world should get their own waste-treatment facilities so they're independent of questionable local contractors, and U.N. staff coming from cholera-endemic countries should be screened for the disease before leaving home or given a prophylactic dose of antibiotics.
Some scientists have called such measures ineffective or impractical (Science, 28 January, p. 388), and Waldor says The New England Journal of Medicine made him strike similar recommendations, deemed “inflammatory,” from a January paper presenting evidence for an Asian connection. But Cravioto says the measures are not that difficult to implement. Ban Ki-moon has said a new panel will study how to put the advice into practice.
The results of two field investigations -- one by a Haitian-French teach headed by French epidemiologist Dr. Renaud Piarroux and the other a United Nations panel of four experts -- became available at about the same time in early May, 2011. The UN panel presented a report which was widely circulated, while the Piarroux et al findings appeared in an advance release of the Emerging Infectious Diseases. Since Piarroux and colleagues had already presented their major findings months earlier in an unpublished report, the main focus of the press was on the UN panel report.
Martin Enserink in Science noted Piarroux's journal article, and reviewed his more complete analyses. Yet he did not emphasize that the two investigations (i.e., Piarroux et al and UN panel) occurred months apart, and thus were based on different histories and findings.
When confronted with the cholera outbreak, the Haitian government requested the assistance of medical colleagues in the French government. The French government in turn requested the services of Renaud Piarroux, MD, PhD, a prominent cholera epidemiologist at the Université de la Méditerranée and the teaching Hospital of Assistance Publique-Hôpitaux de Marseille in Marseille, France. Dr. Piarroux had much experience with cholera in Africa and has also published on cholera interventions by humanitarian organizations. He and colleagues conducted a joint French–Haitian investigation in Haiti during November 7-27, 2010, less than month after the index cases had occurred on October 14, 2010. Hence their epidemiological investigation was conducted close in time to when the specific causative events took place, with full cooperation of the Haitian government.
The United Nations panel, comprised of four international cholera experts, were assembled in December, 2010 and went to Haiti in February 13-20, 201, or four months following the onset of the epidemic. They provided an excellent overview of what took place, added much on the characterization of the organism and the water and sewage flow patterns. Yet their investigation into the disease patterns that occurred in the MINUSTAH camp at Mirebalais was following a trail that was four months old, and perhaps misleading, given the reluctance of the Nepalese UN peacekeepers to cooperate and possibly incriminate themselves. They also appeared to have trouble getting specimens of Vibrio cholearae from the Nepal government that had occurred in September 2010 shortly before the Nepalese peacekeepers left for Haiti. Instead they had to rely for their molecular analysis on the laboratory work of others on samples gathered in Haiti, and on Dr. Dong Wook Kim at the International Vaccine Institute in Korea for specimens from Nepal. Given the reluctance of the government of Nepal to aid the investigation, either in the field or in the laboratory, it brings into question the value of the clinical evidence (i.e., "The medical records were silent.") presented in the UN panel report.
Conversely, the Piarroux et al report and conjecture about the amount of contaminated feces that would need to have been released to infect persons in both Meille and then down river in Mirebalais was based on both experience and careful field investigation, aided by Haitian epidemiologists and public health specialists. To Piarroux, the statements of those at the Nepalese MINUSTAH camp did not correspond with what he observed. Thus he questioned the veracity of the clinical characterizations put forward by the Nepalese peacekeepers.