Sources of Infection & Risk Factors
Cholera is an acute intestinal infection causing profuse watery diarrhea, vomiting, circulatory collapse and shock. Many infections are associated with milder diarrhea or have no symptoms at all. If left untreated, 25-50% of severe cholera cases can be fatal.
A person can get cholera by drinking water or eating food contaminated with the cholera bacterium. Large epidemics are often related to fecal contamination of water supplies or street vended foods. The disease is occasionally spread through eating raw or undercooked shellfish that are naturally contaminated.
People who are more likely to be exposed to cholera include healthcare personnel treating cholera patients, cholera response workers, and travelers in an area of active cholera transmission who cannot or do not always follow safe food and water precautions and personal hygiene measures.
Individuals with achlorhydria (the absence of hydrochloric acid in digestive stomach juices), blood type O, chronic medical conditions, and those without ready access to rehydration therapy and medical services are more likely to have severe disease from cholera and suffer poor outcomes.
Brackish and marine waters are the natural environment for the etiologic agents of cholera, Vibrio cholerae serogroup O1 or O139. There are no known animal hosts for Vibrio cholerae, however, the bacteria attach themselves easily to the chitin-containing shells of crabs, shrimps, and other shellfish, which can be a source for human infections when eaten raw or undercooked.
Epidemic cholera is caused by infection with toxigenic Vibrio cholerae serogroups O1 or O139.
- Only toxigenic strains of serogroups O1 and O139 have caused widespread epidemics and are reportable to the World Health Organization (WHO) as “cholera”.
- V. cholerae O1 has two biotypes, Classical and El Tor, and each biotype has distinct serotypes, Inaba, Ogawa, and rarely Hikojima. The symptoms of infection are indistinguishable, although a higher proportion of persons infected with the El Tor biotype remains asymptomatic or have only a mild illness.
- In recent years, infections with the Classical biotype of Vibrio cholerae O1 have become quite rare and are limited to parts of Bangladesh and India.
Many other serogroups of Vibrio cholerae, with or without the cholera toxin gene, can cause a cholera-like illness, as can non-toxigenic strains of the O1 and O139 serogroups.
In the U.S., the occurrence of cholera is very low (0-5 cases per year) and is usually due to ingestion of contaminated food or international travel. There has been a modest increase in imported cases since 1991 related to travel and ongoing epidemics.
Cholera is a major cause of epidemic diarrhea throughout the developing world. There has been an ongoing global pandemic in Asia, Africa and Latin America for the last six decades. In 2017, a total of 34 countries reported a cumulative total of 1 227 391 cases including 5 654 deaths (case fatality rate of 0.5%) to the World Health Organization (WHO) 1. Cholera is underreported, and as many as 2.9 million cases, and 95,000 deaths are suspected to occur each year. Resource-poor areas continue to report the vast majority of cases, with the African continent having the highest case fatality rates.
Large population migrations into urban centers in developing countries are straining existing water and sanitation infrastructure and increasing disease risk. Epidemics are a marker for poverty and lack of basic sanitation. Multiple routes exist for spreading cholera, meaning that successful prevention may require different measures in different areas.
Natural infection and currently available vaccines offer incomplete protection of relatively short duration; no multivalent vaccines are available for O139 infections.
Simple rehydration treatment saves lives, but logistics of delivery in remote areas remains difficult during epidemic periods. Accompanying antibiotic treatment is helpful but may be difficult because of growing antimicrobial resistance. Natural reservoirs for the bacterium in warm coastal waters make eradication very unlikely.