Lessons, scientific clues emerge from Haiti's cholera outbreak

Oct 17, 2011 (CIDRAP News) – The first cases in Haiti's cholera outbreak were confirmed nearly a year ago, and public health lessons from the experience and scientific clues about the Vibrio cholerae strain continue to emerge, including new details from the US Centers for Disease Control and Prevention (CDC) and its research partners.

The CDC recently published four new reports on cholera in Haiti in an early online edition of its journal Emerging Infectious Diseases (EID). One describes the CDC's response to the outbreak, highlighting lessons learned from the experience.

The other three are research reports that address the genetic relatedness of Haiti's outbreak strain to cholera circulating in Asia and Africa, cholera control in Port-au-Prince, and the outbreak strain's microbial resistance.

The CDC experts were already on the ground in Haiti assisting with earthquake response when the first cholera cases were reported, according to a report by Jordan Tappero, MD, MPH, director of the health systems reconstruction office in the CDC's Center for Global Health, and Robert Tauxe, MD, MPH, deputy director of the CDC's Division of Foodborne, Waterborne, and Environmental Diseases.

Haiti's health ministry had asked the CDC to help it strengthen the country's disease surveillance and laboratory capacity in the wake of the natural disaster, which the authors said helped rapidly detect cholera when it appeared on the scene.

Tappero and Tauxe noted that the availability of safe water and sanitation in Haiti were already in danger before the earthquake struck: Only 63% had access to an improved water source, and 17% had access to a latrine.

Early in the health ministry's cholera outbreak response, the CDC and other partners helped it identify that untreated drinking water was the primary source of cholera, which drove the push to distribute water purification tablets and show Haitians how to use them. The CDC also developed materials on cholera treatment and helped train local health providers.

Emergency funds from the US government helped nongovernmental organizations shore up their clinical capacity and provided emergency water treatment supplies for households and piped water systems.

Tappero and Tauxe warn that cholera may increase seasonally in Haiti each year during the rainy season, but said it's difficult to predict the future burden of the disease, based on uncertainty surrounding the proportion of the population that has now been immunized by natural infection and how long the protection might last.

Going forward, Haiti's challenges will include managing cholera treatment with limited resources and ensuring that people in earthquake disaster camps, where water and sanitation tend to be better than elsewhere, transition to more permanent living quarters that have safe water and adequate sewage systems.

The two experts wrote that Haiti's experience is a reminder that cholera is a threat anywhere in the world where people drink untreated water and have poor sanitation. "The epidemic also shows how cholera can emerge where it is least expected," noting that it appeared first in rural Haiti instead of a more urban setting, such as crowded camps in Port-au-Prince.

Cholera's more moderate impact in the neighboring Dominican Republic and the that fact that it mostly spared the displaced-persons camps shows how safer water and sanitation can prevent transmission, they wrote. Economic experts have estimated a $750 million price tag for improved water and sanitation, which Tappero and Tauxe said would fall well within the more than $6 billion range that countries have pledged for Haiti's earthquake relief.

In another new EID report, an international group of researchers, including some from the CDC, described the work of a task force that explored the ancestry of Haiti's cholera outbreak strain using whole-genome sequencing. They looked at 23 isolates from recent clinical infections, comparing 9 from Haiti and the Dominican Republic with 12 from Asia and Africa and 2 others from the Western Hemisphere.

The authors noted that 2010 isolates from Nepal were not available for analysis. Epidemiological studies have suggested an outside source for Haiti's cholera outbreak, most likely United Nations peacekeepers from Nepal who came to Haiti to assist with earthquake response.

The group's phylogenetic analysis suggested that the outbreak strain is genetically related to cholera strains originating in India, with a potential link to an isolate from Cameroon.

Genetic analysis of Haiti's cholera strain could have global implications, because it is more infective and ecologically fit, and this antibiotic-resistant strain could become endemic and cause future outbreaks, they wrote.

Though the number if isolates they explored is too small to conclusively show how cholera was introduced into Haiti, their analysis provides clear evidence that it came from an outside source, not a local aquatic environment, according to the report.

In an effort to explore cholera transmission in Port-au-Prince, CDC researchers and their colleagues in Haiti conducted a case-control study in December 2010, about 2 months into the cholera outbreak, to explore health practices that may have influenced disease spread.

Their study included 53 case-patients from a cholera treatment center in a slum and 106 neighborhood-matched controls.

Researchers found that though water sources did not differ between cases and controls, food diversity, proper hand washing, and treating drinking water were factors that were protective against illnesses in an urban setting, though treating drinking water did not reach statistical significance. They suggested that food diversity could have been a proxy for improved nutrition.

They concluded that the findings underscore the importance of personal hygiene in preventing cholera in a contaminated urban environment.

In the fourth study, researchers from the CDC, Canada, and Haiti explored 122 clinical isolates from Haiti to characterize drug-resistance mechanisms.

All showed susceptibility to azithromycin and tetracycline, reduced sensitivity to ciprofloxacin, and resistance to furazolidone, nalidixic acid sulfisoxazole, streptomycin, and trimethoprim/sulfamethoxazole.

Sequencing also detected the floR gene commonly associated with chloramphenicol resistance, though it did not confer resistance in the Haiti strain, possibly due to lower expression levels, the group wrote.

Drug-resistant cholera infections are a global health concern, because they can be more severe and difficult to treat, the authors concluded, urging health providers to restrict antibiotic treatment to patients who are severely dehydrated.

Tappero JW, Tauxe RV. Lessons learned during public health response to cholera epidemic in Haiti and the Dominican Republic. Emerg Infect Dis 2011 Nov;17(11) [Full text]

Reimer AR, Domselaar GV, Stroika S, et al. Comparative genomics of Vibrio cholerae from Haiti, Asia, and Africa. Emerg Infect Dis 2011 Nov;17(11) [Full text]

Dunkle SE, Mba-Jonas A, Loharikar A, et al. Epidemic cholera in a crowded urban environment, Port-au-Prince, Haiti. Emerg Infect Dis 2011 Nov;17(11) [Full text]

Sjolund-Karlsson M, Reimer A, Folster JP, et al. Drug-resistance mechanisms in Vibrio cholerae O1 outbreak strain, Haiti, 2010. Emerg Infect Dis 2011 Nov;17(11) [Full text]

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