Introduction of Vibrio cholerae to Haiti during the deployment of United Nations (UN) peacekeepers in 2010 resulted in one of the largest cholera epidemics of the modern era. Following the outbreak, a UN-commissioned independent panel recommended three pre-deployment intervention strategies to minimize the risk of cholera introduction in future peacekeeping operations: screening for V. cholerae carriage, administering prophylactic antimicrobial chemotherapies, or immunizing with oral cholera vaccines. However, uncertainty regarding the effectiveness of these approaches has forestalled their implementation by the UN. We assessed how the interventions would have impacted the likelihood of the Haiti cholera epidemic.
Methods and Findings
We developed a stochastic model for cholera importation and transmission, fitted to reported cases during the first weeks of the 2010 outbreak in Haiti. Using this model, we estimated that diagnostic screening reduces the probability of cases occurring by 82% (95% credible interval: 75%, 85%); however, false-positive test outcomes may hamper this approach. Antimicrobial chemoprophylaxis at time of departure and oral cholera vaccination reduce the probability of cases by 50% (41%, 57%) and by up to 61% (58%, 63%), respectively. Chemoprophylaxis beginning 1 wk before departure confers a 91% (78%, 96%) reduction independently, and up to a 98% reduction (94%, 99%) if coupled with vaccination. These results are not sensitive to assumptions about the background cholera incidence rate in the endemic troop-sending country. Further research is needed to (1) validate the sensitivity and specificity of rapid test approaches for detecting asymptomatic carriage, (2) compare prophylactic efficacy across antimicrobial regimens, and (3) quantify the impact of oral cholera vaccine on transmission from asymptomatic carriers.
Screening, chemoprophylaxis, and vaccination are all effective strategies to prevent cholera introduction during large-scale personnel deployments such as that precipitating the 2010 Haiti outbreak. Antimicrobial chemoprophylaxis was estimated to provide the greatest protection at the lowest cost among the approaches recently evaluated by the UN.
A cholera outbreak modeling study reveals that chemprophylaxis treatment for deployed peacekeepers in Haiti would have reduced the risk of disease introduction by 90%.
Cholera—a bacterial gut infection caused by Vibrio cholerae—is a global killer. Epidemics (outbreaks) of cholera in countries across Africa, Asia, and South and Central America where cholera is endemic (always present) affect 1–4 million people and kill up to 142,000 people every year. People get cholera by eating food or drinking water contaminated with feces from an infected person, so cholera epidemics occur in places with poor sanitation such as refugee camps and in regions where an earthquake or another natural disaster has disrupted water and sanitation systems. Most people who become infected with V. cholerae have no or mild symptoms, but these asymptomatically infected individuals can shed bacteria in their feces for up to 2 wk. Other infected people develop severe diarrhea, producing profuse watery feces. The standard treatment for cholera is replacement of fluids and salts lost through diarrhea with oral rehydration fluid or, in the worst cases, by fluid replacement directly into a vein. If left untreated, patients with severe cholera can die from dehydration within hours of developing symptoms.
Why Was This Study Done?
In 2010, a large cholera epidemic affected Haiti, which had been free of cholera for more than a century. This epidemic, which has resulted in nearly 9,000 deaths to date, was probably caused by contamination of water by infected sewage from the MINUSTAH (Mission des Nations Unies pour la stabilisation en Haïti) base, a UN peacekeeping mission established in Haiti in 2004. In January 2010, a massive earthquake hit Haiti, and in October that year, 454 troops from Nepal (a cholera-endemic country) were deployed to a MINUSTAH base in central Haiti as part of an ongoing peacekeeping operation to maintain political stability. Following the Haiti cholera outbreak, a panel of experts recommended that peacekeeping troops coming from countries where cholera is endemic should be screened for V. cholerae carriage, treated prophylactically with antimicrobial drugs (prophylactic treatments prevent a disease occurring), and/or immunized with oral cholera vaccines before deployment. However, because of uncertainty about the effectiveness of these pre-deployment intervention strategies, the UN has not implemented any of them. Here, the researchers use computational modeling to investigate whether these interventions would have prevented the Haiti cholera outbreak.
What Did the Researchers Do and Find?
The researchers developed a mathematical model to simulate the arrival of asymptomatically infected peacekeepers (or those with mild illness that would not have prevented their deployment) and the dynamics of cholera transmission from the MINUSTAH base to the community. They used this model to investigate the effect of the three proposed pre-deployment intervention strategies on (1) the probability of undetected importation of V. cholerae from an endemic source country by an asymptomatically infected peacekeeper, and (2) the subsequent probability of transmission of V. cholerae from peacekeepers to the general public, two events needed to establish an epidemic. According to the model, diagnostic screening reduced the probability of cases occurring by 82%, whereas antimicrobial chemoprophylaxis at the time of departure and oral cholera vaccination reduced the probability of cases by 50% and 61%, respectively. Chemoprophylaxis beginning a week before deployment reduced the probability of cases by 91% when used alone and by 98% when coupled with vaccination. Finally, the researchers estimated that antimicrobial chemoprophylaxis with conventional therapies would cost under US$1 per peacekeeper, whereas the other two pre-deployment intervention strategies would be considerably more expensive.
What Do These Findings Mean?
The accuracy of these findings is likely to be affected by the many assumptions made by the researchers in constructing their mathematical model. In addition, further research is needed to validate the use of rapid tests for detecting asymptomatic V. cholerae carriage, to compare the prophylactic efficacy of different antimicrobial regimens, and to quantify the impact of oral cholera vaccination on disease transmission from asymptomatic carriers. Nevertheless, these findings, which are likely to be generalizable to other settings, suggest that screening, chemoprophylaxis, and vaccination would all effectively prevent cholera introduction during large-scale personnel deployments like the one that precipitated the cholera outbreak in Haiti. However, although antimicrobial chemoprophylaxis is likely to provide the greatest protection at the lowest cost, this strategy is controversial because of increasing levels of drug resistance. Moreover, the researchers stress that proper sewage disposal must be implemented in tandem with any biomedical intervention designed to limit the risk of cholera introduction into disease-free areas by peacekeepers or other troops.
This list of resources contains links that can be accessed when viewing the PDF on a device or via the online version of the article at http://dx.doi.org/10.1371/journal.pmed.1001947.
The World Health Organization provides information about cholera in several languages
The US Centers for Disease Control and Prevention also provides information about cholera for the public, medical professionals and travelers, specific information about the cholera epidemic in Haiti published a year into the outbreak, and CDC videos about defeating cholera and managing dehydration (in English, French and Spanish) are available
The UK National Health Service (NHS) Choices website provides information about cholera
Information about the UN in Haiti is available, including information on fighting cholera in the country, a recent fact sheet about the ongoing cholera epidemic, and a warning that cholera eradication in Haiti will take many years
The United Nations has published the report of the Independent Panel of Experts on the Cholera Outbreak in Haiti and its own follow-up to the panel’s policy recommendations
The not-for-profit organization Médecins Sans Frontières (MSF) is tackling several cholera outbreaks around the world; its website includes a 2014 report about the cholera epidemic in Haiti
MedlinePlus provides links to further resources about cholera