Merck Manual

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Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Last full review/revision Feb 2020| Content last modified Feb 2020
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Cholera is a serious infection of the intestine that is caused by the gram-negative bacteria Vibrio cholerae and that causes severe diarrhea, which can be fatal without treatment.

  • People are infected when they consume contaminated food, often seafood, or water.

  • Cholera is rare except in areas where sanitation is inadequate.

  • People have watery diarrhea and vomit, usually with no fever.

  • Identifying the bacteria in a stool sample confirms the diagnosis.

  • Replacing lost fluids and giving antibiotics treat the infection effectively.

(See also Overview of Bacteria.)

Several species of Vibrio bacteria cause diarrhea (see Table: Microorganisms That Cause Gastroenteritis). The most serious illness, cholera, is caused by Vibrio cholerae. Cholera may occur in large outbreaks.

Vibrio cholerae infection is acquired by consuming water, seafood, or other foods contaminated by the stool of infected people. Once infected, people excrete the bacteria in stool. Thus, the infection can spread rapidly, particularly in areas where human waste is untreated.

Once common throughout the world, cholera is now largely confined to developing countries in the tropics and subtropics. It is common (endemic) in parts of Asia, the Middle East, Africa, and South and Central America. Small outbreaks have occurred in Europe, Japan, and Australia. In the United States, cholera can occur along the coast of the Gulf of Mexico.

Large outbreaks of cholera continue to occur wherever there is poverty and people lack access to clean drinking water and sanitary disposal of human waste. A severe cholera epidemic occurred in Haiti after the earthquake in 2010 and lasted until 2017. During this outbreak, 700,000 people became ill, and 9,000 died. An outbreak in Yemen started in 2016 and has not yet ended. This outbreak has had even greater devastating effects. Over 1 million people in Yemen have become ill, and over 2,000 have died. It is thought to be the largest, fastest-spreading cholera outbreak in modern history.

In endemic areas, outbreaks usually occur when war or civil unrest disrupts public sanitation services. Infection is most common during warm months and among children. In newly affected areas, outbreaks may occur during any season and affect all ages equally.

For infection to develop, many bacteria must be consumed. Then, there may be too many for stomach acid to kill, and some bacteria can reach the small intestine, where they grow and produce a toxin. The toxin causes the small intestine to secrete enormous amounts of salt and water. The body loses this fluid as watery diarrhea. It is the loss of water and salt that causes death. The bacteria remain in the small intestine and do not invade tissues.

Because stomach acid kills the bacteria, people who produce less stomach acid are more likely to get cholera. Such people include

  • Young children

  • Older people

  • People taking drugs that reduce stomach acid, including proton pump inhibitors (such as omeprazole) and histamine-2 (H2) blockers (such as famotidine)

People living in endemic areas gradually acquire some immunity.

Did You Know...

  • Without treatment, more than one half of people with severe cholera die.


Most infected people have no symptoms.

When cholera symptoms occur, they begin 1 to 3 days after exposure, usually with sudden, painless, watery diarrhea and vomiting. Usually, people have no fever.

Diarrhea and vomiting may be mild to severe. In severe infections in adults, more than 1 quart (1 liter) of water and salts is lost per hour. The stool looks gray and has flecks of mucus in it. It is described as rice-water stool. Within hours, dehydration can become severe, causing intense thirst, muscle cramps, and weakness. Very little urine is produced. The eyes may become sunken, and the skin on the fingers may become very wrinkled. If dehydration is not treated, loss of water and salts can lead to kidney failure, shock, coma, and death.

In people who survive, cholera symptoms usually subside in 3 to 6 days. Most people are free of the bacteria in 2 weeks. The bacteria remain in a few people indefinitely without causing symptoms. Such people are called carriers.


  • Culture of a sample of stool

Doctors take a sample of stool or use a swab to obtain a sample from the rectum. It is sent to a laboratory where cholera bacteria, if present, can be grown (cultured). Identifying Vibrio cholerae in the sample confirms the diagnosis. Doctors may use the polymerase chain reaction (PCR) technique to increase the amount of the bacteria's genetic material (DNA), so that the bacteria can be detected more quickly.

Blood and urine tests to evaluate dehydration and kidney function are done.


The following are essential to cholera prevention:

  • Purification of water supplies

  • Appropriate disposal of human waste

In areas where cholera occurs, other precautions include

  • Using boiled or chlorinated water

  • Avoiding uncooked vegetables and undercooked fish and shellfish

Shellfish tend to carry other forms of Vibrio as well.


In the United States, a cholera vaccine is available for people aged 18 to 64 years old if they are traveling to areas where cholera occurs. It is taken by mouth in a single dose. However, whether this vaccine is effective for more than 3 to 6 months is unknown.

Two other vaccines for cholera are available outside the United States. These vaccines provide 60 to 85% protection for up to 5 years. These vaccines are taken by mouth in two doses. Booster doses are recommended after 2 years for people who continue to be at risk of getting cholera.


  • Fluids that contain salt

  • An antibiotic

Replacement of lost body water and salts

Rapid replacement of lost body water and salts is lifesaving. Most people can be treated effectively with a solution given by mouth. These solutions are designed to replace the fluids the body has lost.

For severely dehydrated people who cannot drink, a salt solution is given intravenously.

In epidemics, if the intravenous solution is not available, people are given a salt solution by mouth or, if needed, through a tube inserted through the nose into the stomach. After enough fluids are replaced to relieve symptoms, people should drink at least enough of the salt solution to replace the fluids they have lost through diarrhea and vomiting.

People are also encouraged to drink as much water as they want. Solid foods can be eaten after vomiting stops and appetite returns.

More than 50% of untreated people with severe cholera die. Fewer than 1% of people who receive prompt, adequate fluid replacement die.


An antibiotic is usually given to reduce the severity of diarrhea and make it stop sooner. Also, people who take an antibiotic are slightly less likely to spread the infection during an outbreak.

Antibiotics that may be used include doxycycline, azithromycin, and ciprofloxacin. Each of these antibiotics is taken by mouth. Doctors choose antibiotics that are known to be effective against the bacteria causing cholera in the local community. Because doxycycline may discolor the teeth in children under 8 years old, these children are given azithromycin instead.

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