Cholera Outbreak in Haiti Continues

This cholera patient is drinking oral rehydration solution in order to counteract his cholera-induced dehydration. Photo: CDC/1992.Cholera affects 3-5 million people each year, killing more than 100,000. The diarrheal disease, spread by contaminated food and water, is often a major problem in disaster areas where a clean water supply and sanitation facilities are limited or unavailable.

Haiti, still recovering from the 7.0-magnitude earthquake that devastated Port-au-Prince on January 12, 2010, is experiencing a growing cholera outbreak that has so far killed 259 people. Haiti’s Le Ministère de la Santé Publique et de la Population (Ministry for Public Health and the Population, or MSPP) reported 3,342 confirmed cases as of October 26, but Dr. Jon Andrus, Deputy Director of the Pan American Health Organization (PAHO) stated in a press briefing on October 25 that the true number of cases is likely to be significantly higher than the confirmed number. Dr. Andrus noted that about 75% of people infected with cholera do not experience symptoms (called “asymptomatic infection”). These individuals can still spread the bacteria, however. Dr. Andrus also stated that while the increase in new cases has recently slowed, there is still a concern that the Haitian outbreak could spread to the Dominican Republic.

In extreme cases, cholera is among the most rapidly fatal infectious diseases: a previously healthy person can become severely dehydrated and die within one day without treatment. Among most people with symptomatic infections, however, about 80% experience only mild or moderate symptoms. About 20% develop watery diarrhea that can cause severe dehydration.

Mild cases can be treated outside of health care facilities with oral rehydration salts. These replace fluids lost as a result of diarrhea. More serious cases require intravenous rehydration fluids as well as antibiotics that are effective against the Vibrio cholerae bacterium. A recent study has found that ciprofloxacin, a standard antibiotic treatment for cholera, is decreasing in efficacy. While a single dose of ciprofloxacin had a clinical success rate of 93% in 1993-1994, that rate dropped to 27% by 2003-2004. The same study found that a single dose of azithromycin, a different antibiotic, could outperform as many as six doses of ciprofloxacin in treating cholera. Although these findings are preliminary, both could have implications for treatment during emergency situations, where administration of multiple doses over time may not be feasible. Dr. Andrus noted that the strain of cholera circulating in Haiti is susceptible to antibiotics.

In addition to treatment in response to infection, preventive methods are also available against cholera. The primary means of prevention are via good personal hygiene and clean water. In an emergency situation such as that occurring in Haiti, where more than half of reported cholera deaths are occurring outside hospitals and among the community, proper disposal of bodies is also an issue—fluids from the remains of cholera victims can also spread the bacteria.

Clean water and good hygiene initiatives are primarily favored against cholera, particularly because they can provide long-term protection against the disease. Although vaccines against cholera are available, they are not recommended in the United States and other countries with good sanitation and water systems. In countries with limited sanitation facilities and water supplies, however, vaccination can play a key role in cholera prevention.

Currently two vaccine types exist against cholera. Both are oral vaccines. The first, Dukoral, was licensed in 1991. Dukoral is a monovalent (protection against one strain) killed whole-cell plus recombinant cholera toxoid B subunit vaccine (see our article on Different Types of Vaccines for more information!). In addition to offering protection against cholera, Dukoral also provides some protection against enterotoxigenic E. coli. Dukoral is given in two doses seven or more days apart for adults and children six years of age or older. Children between two and five years old need three doses; it is not licensed for children younger than two.

The second vaccine was first licensed as ORCVAX in 1997. It was reformulated in 2004 and licensed as mORCVAX in Viet Nam and Shanchol in India. This vaccine is a bivalent (protection against two strains) oral vaccine; it does not offer protection against E. coli. It is given in two doses 14 days apart for adults and children one year of age and older.

Both of these vaccines require a cold chain—that is, a supply chain between the manufacturing facility and the final destination of the vaccine that offers temperature control. This can be a major issue in remote areas, and in disaster-stricken regions. However, when successfully delivered to and administered in at-risk areas, both vaccines have a protective efficacy of greater than 50% against cholera. (Studies have shown widely varying levels of protection; additional research is in progress.) Research has also suggested that cholera vaccination can result in significant herd immunity against the disease as well as providing individual protection.

The World Health Organization (WHO) officially recommends that immunization with cholera vaccines be used in conjunction with other prevention strategies in areas at risk for outbreaks. In areas where resources are limited, WHO recommends cholera immunization that is targeted at high-risk children, using Shanchol for children one year of age or older, and Dukoral for children two or older.

Several live attenuated vaccines against cholera are also in development with the potential to provide long-term protection via a single dose. According to WHO, however, none of these vaccines is likely to become available within the next few years.

Readers may be interested in this video from the 2010 meeting of the Infectious Diseases Society of America featuring an interview with Stephen Calderwood, MD, of Massachusetts General Hospital in Boston. Dr. Calderwood, a world expert on cholera, discusses the typical presentation of the disease as well as its treatment, and the ongoing outbreak in Haiti.

 

Sources

Khan WA et al. Single-dose azithromycin is superior to 6-dose ciprofloxacin in adult cholera: Results of a double-blind randomized controlled trial. IDSA 2010; Abstract 207.

Ali M et al. Herd immunity conferred by killed oral cholera vaccines in Bangladesh: a reanalysis.
The Lancet, 2005. 366:(44-49).

Pan American Health Organization. Emergency Operations Center Situation Report #4: Cholera Outbreak in Haiti. October 25, 2010.

World Health Organization. Fact sheet: Cholera. June 2010. Accessed October 26, 2010. Available at http://www.who.int/mediacentre/factsheets/fs107/en/index.html.

World Health Organization. Weekly epidemiological record. 26 MARCH 2010. 85:13 (117–128).

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