Cholera is an intestinal infection caused by toxigenic Vibrio cholerae, group O-1 or O-139. Natural and man-made disasters which produce overcrowding, a scarcity of safe drinking water, improper elimination of human waste, and the contamination of food during or after its preparation are risk factors for the spread of the disease.
In areas where cholera has not been confirmed, a suspected case is defined as severe dehydration or death from acute watery diarrhea in a patient over 5 years of age.
In areas where an epidemic is under way, a suspected case of cholera is defined as acute watery diarrhea, with or without vomiting, in a patient over 5 years of age.
A confirmed case of cholera is defined as the laboratory-confirmed presence of V. cholerae 01 in any patient with diarrhea. Once the presence of the disease has been confirmed, it is unnecessary to examine specimens from all cases or contacts. Monitoring should include ongoing laboratory confirmation of a small proportion of cases.
It is important to adopt this definition. However, for clinical management of cases of acute watery diarrhea in an area in which an epidemic is under way, cholera should be suspected in all cases in patients aged 2 or older. It should be noted that in Central America, cholera primarily strikes adults, with 80% of the recorded cases representing individuals 5 years of age or older, while 80% of diarrheal diseases from other causes occur in children under 5.
There are more than 60 serogroups of Vibrio cholerae, but only the O1 serogroup causes cholera. V. cholerae occurs as two biotypes: classical and El Tor. Each biotype has two serotypes: Ogawa and Inaba. The El Tor biotype (first isolated in Egypt in 1905) is responsible for almost all the recent outbreaks of the disease, producing a greater proportion of asymptomatic infections than the classical biotype and surviving longer in the environment. This biotype can live in association with certain aquatic plants and animals, which makes water an important reservoir of the infection.
The second cholera pandemic spanned the period 1826 to 1837. This was the first pandemic that ravaged England and Western Europe, causing thousands of deaths in early 1830. The epidemic spread to Canada, the United States, and Mexico in continental North America, to Guyana in South America, and to Cuba.
In January 1991 Vibrio cholerae 01 reached a town on the coast of Peru, trumpeting the arrival of the seventh cholera pandemic in Latin America. By the year 2000 the epidemic had spread to 21 of the 35 countries of the Region of the Americas, with Canada, Uruguay, and the Caribbean remaining free of the disease. Moreover, in 1999 Argentina, Bolivia, Chile, Costa Rica, French Guiana, Guyana, Paraguay, Panama, and Suriname did not report cases of the disease.
In the 19th and early 20th century cholera was a predominantly urban phenomenon with high case-fatality rates (30-50%). In contrast, the Latin American epidemic of the 1990s was rural, with lower case-fatality rates (around 2%). The disease is also becoming endemic, and an incipient seasonal epidemiological model can be observed.
People who follow the usual tourist itineraries and observe food safety recommendations face practically no risk when visiting countries that have reported cases of cholera.
Q. When we speak of cholera we often refer to it as a pandemic. What is a "pandemic"?
A pandemic is a disease that strikes the majority of the population in a large region, emerges simultaneously in different parts of the world, and is a long-term phenomenon.
Q. Is cholera as widespread and serious now as it used to be?
No. In the 19th century cholera was found in major cities, causing high case-fatality rates (30%-50%), while today the infection is often mild, self-limiting, or subclinical and is found in rural areas, with relatively low case-fatality rates (2%).
Q. What led to the changes in the model of the disease?
The following factors can be mentioned: (a) El Tor, a biotype of V. cholerae in circulation, which produces a greater proportion of asymptomatic cases than the classical biotype; (b) greater access to safe drinking water; (c) better excreta disposal systems; (d) health education, and (e) primary health care.
Q. Is it possible to contract V. cholerae through person-to-person contact?
It is possible, but this type of transmission is very rare.
Q. What are the main steps in managing a suspected case of cholera?
The main steps are: assess for dehydration, rehydrate with a solution of oral rehydration salts, observe the patient, replace missing fluids, administer oral antibiotics only to patients with serious dehydration, and feed the patient.
Q. Do we need a health system with a high level of complexity to treat cholera?
Fluids and simple electrolyte replacement therapy produce excellent results in the majority of cases. Serious cases may require antibiotics (doxycycline or tetracycline for adults; trimethoprim sulfamethoxazole for children). These interventions can be carried out at the primary level.
Q. Are travel and trade restrictions recommended in outbreaks of cholera?
No. Travel and trade restrictions between countries or between different areas of a country do not prevent the spread of cholera. Not only are they ineffective, they lead to the suppression of information on outbreaks of the disease. WHO modified its International Health Regulations in 1973 so that travelers would no longer be required to show a certificate of vaccination against cholera.
Q. Are vaccinations recommended for cholera control?
No. The traditional vaccine against cholera (based on whole, killed cells) is characterized by low levels of efficacy and high reactogenicity. Therefore, it is not recommended for the control of epidemics. The new vaccines might be considered, but with these, there is a rapid loss of protection, giving people a false sense of security. Resources should be channeled to the most useful control methods.
Q. How do we protect young children against cholera?
In infants under 6 months, breast-feeding protects against the disease. Careful preparation of formula and food with safe drinking water should protect infants who are not breast-fed.
Q. Is it mandatory to report cholera outbreaks?
Yes. The diseases listed as reportable by the International Health Regulations are cholera, yellow fever, and the plague. WHO publishes the data on cholera outbreaks in the Weekly Epidemiological Record; the CDC publishes its semiweekly "Health Information for International Travel" to inform the public about where cholera and yellow fever have been reported.
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Dr. Marlo Libel
Phone: (202) 974-3129