Cholera Incidence 10 Times Higher Than Official Reports

Jenni Laidman

March 05, 2012

March 5, 2012 — Cholera rates worldwide are some 10 times higher than official reports indicate, and more of than half of those cases are in children younger than 5 years, according to a report published online January 24 in the Bulletin of the World Health Organization (WHO).

Mohammad Ali, PhD, senior scientist and head of the Data Management, GIS, and Statistics Unit of the International Vaccine Institute, Seoul National University Research Park, Republic of Korea, and colleagues examined data reported to WHO, as well as medical literature, alternative disease monitoring systems, previous multicountry studies, data from the Global Infectious Disease and Epidemiology Network database, media reports, and online government reports to arrive at the estimates.

The report found cholera kills between 100,000 and 120,000 people annually, which is many more than the officially reported 7543 deaths caused by 317,534 cholera cases.

According to the report, an estimated 2.8 million (uncertainty range, 1.2 - 4.3 million) people contract cholera each year in endemic countries around the world, and some 91,000 (uncertainty range, 28,000 - 142,000) people die from infection by the bacteria Vibrio cholerae O1 and O139. In nonendemic countries, the report estimates, another 87,000 cholera cases cause 2500 deaths annually.

Children younger than 5 years are the most vulnerable to infection, with nearly half of all cholera cases occurring in that age group. The estimated cholera incidence rate for children younger than 1 years is 7.3 cases per 1000 in endemic areas, and for children aged 1 to 4 years, it is 7.0 per 1000. Children in the next age group, 5 to 14 years, have an incidence rate less than one third of the youngest group, at 2.2 per 1000.

Creating a clearer picture of cholera's devastation is a critical first step to determining where to concentrate prevention efforts, Dr. Ali said.

"If cases are not reported then resources cannot be allocated to deal adequately with the disease," he said in a WHO press release. "Policymakers need to know the burden of disease and the population at risk."

Although United Nations members are required to report cholera to WHO, member states generally underreport outbreaks of the diarrheal disease because of the potential effect on tourism and trade, the report states. Also contributing to underreporting is the inability of poor countries to initiate systematic surveillance. Another factor is that, "Many deaths in developing countries probably occur before patients reach the hospital, so statistics are likely to be underestimated," Dr. Ali said in the release.

In addition to upgraded sanitary systems and water systems as preventive measures against cholera, WHO recommends cholera immunization in endemic areas, has approved a new oral cholera vaccine for United Nations purchase, and is evaluating a recently licensed oral vaccine that is less expensive.

According to the new study, some 1.4 billion people live in cholera-endemic areas, with Bangladesh and India having the largest at-risk populations. The cholera incidence rate is 2.0 (range, 0.10 - 4.0) cases per 1000 people in endemic areas, and the mortality rate is about 6.3 deaths per 100,000 people at risk. Mortality rates vary from 0.1 per 100,000 in the Eastern Mediterranean region, which includes Pakistan and Somalia, and the Western Pacific Region, to 15.2 deaths per 100,000 in some parts of Africa.

In the region of the Americas, only Brazil and Paraguay have reported nonimported cholera cases in the last 9 years: Brazil reported 5 cases in 2005, and Paraguay reported 5 cases in 2009. In Europe, only Poland, the Russian Federation, and the Ukraine have reported nonimported cases (1 case each) since 2005. The WHO considers these regions cholera-free. The report does not include the cholera outbreak in Haiti, which began in 2010, after data gathering was complete. Before that outbreak, Haiti had not reported a case of cholera for 100 years, the report states.

The authors have disclosed no relevant financial relationships.

Bull World Health Organ. 2012;90:209-218A. Full text

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