ByLarry M. Bush, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University
Reviewed/Revised Nov 2022 | Modified Sep 2023

Leptospirosis is a potentially serious infection caused by Leptospira, which are spiral-shaped bacteria called spirochetes.

  • Most people are infected through contact with contaminated soil or water during outdoor activities.

  • Fever, headache, and other symptoms occur in two phases, separated by a few days.

  • A severe, potentially fatal form damages many organs, including the liver and kidneys.

  • Detecting antibodies against the bacteria in blood or identifying the bacteria in a sample taken from infected tissue confirms the diagnosis.

  • Infections are treated with antibiotics and, if severe, sometimes with fluids given intravenously and dialysis.

(See also Overview of Bacteria.)

Leptospirosis occurs in many wild and domestic animals, including rats, mice, and dogs, and farm animals such as cattle, horses, sheep, goats, and pigs. Some animals act as carriers and pass the bacteria in their urine. Others become ill and die. People acquire these infections directly through contact with infected animals or indirectly through soil or water contaminated by urine from an infected animal.

Leptospirosis is an occupational disease of farmers and sewer and slaughterhouse workers. However, in the United States, most people become infected during outdoor activities when they come in contact with contaminated soil or fresh water, particularly while swimming or wading. Outside the United States, outbreaks have occurred after heavy rainfall or freshwater flooding. Leptospira can survive for several weeks to months in sources of fresh water (such as lakes and ponds). However, they can survive for only a few hours in salt water.

The 100 to 200 infections reported every year in the United States occur mainly in the late summer and early fall. Because mild leptospirosis typically causes vague, flu-like symptoms that go away on their own, many infections are probably unreported.

Symptoms of Leptospirosis

In about 90% of infected people, leptospirosis symptoms are not serious. In the rest, the disorder involves many organs. This potentially fatal form of leptospirosis is called Weil syndrome.

Leptospirosis usually occurs in two phases:

  • First phase (septicemic phase): About 5 to 14 days after infection occurs, fever, headache, sore throat, severe muscle aches in the calves and back, and chills occur suddenly. The eyes usually become very red on the third or fourth day. Some people cough, occasionally bringing up blood, and have chest pain. Most people recover within about 1 week.

  • Second phase (immune phase): In some people, symptoms return a few days later. They result from inflammation caused by the immune system as it eliminates the bacteria from the body. The fever returns, and the tissues covering the brain and spinal cord (meninges) may become inflamed. This inflammation (meningitis) causes a stiff neck and headache. The lungs can be severely damaged.

If leptospirosis develops during pregnancy, the risk of miscarriage is increased.

Weil syndrome

Weil syndrome can occur during the second phase. It causes fever, jaundice (yellowish discoloration of the skin and whites of the eyes that is caused by liver damage), kidney failure, and a tendency to bleed. People may have nosebleeds or cough up blood, or bleeding may occur within tissues in the skin, lungs, and, less commonly, digestive tract. Anemia can develop. Although the liver and kidneys are the organs most commonly affected, the lungs and heart may also be severely affected.

People who do not develop jaundice recover. About 5 to 10% of people with jaundice die, and this percentage is higher in those over age 60. Risk of death is higher if changes in mental function, kidney failure, respiratory failure, and internal bleeding occur.

Diagnosis of Leptospirosis

  • Culture of blood and urine samples or sometimes a sample of cerebrospinal fluid (obtained by spinal tap)

  • Blood tests for leptospirosis antibodies or genetic material

Doctors suspect leptospirosis when characteristic symptoms occur in people who have traveled to an area where an outbreak is occurring.

To confirm the diagnosis of leptospirosis, doctors take a sample of blood and urine. These samples are analyzed.

If people have symptoms of meningitis, doctors do a spinal tap (lumbar puncture) to obtain a sample of the fluid that surrounds the brain and spinal cord (cerebrospinal fluid).

Usually, several samples are taken over several weeks. These samples are sent to a laboratory to grow (culture) the bacteria.

Identifying the bacteria in cultures or, more commonly, detecting antibodies against the bacteria in blood confirms the diagnosis. The polymerase chain reaction (PCR) technique, which produces many copies of a gene, may be used. It helps doctors diagnose leptospirosis quickly.

Prevention of Leptospirosis

Treatment of Leptospirosis

  • Antibiotics

  • For Weil syndrome, possibly blood transfusions and hemodialysis

Mild infections

For severe infections,

People with severe infection (Weil syndrome) may need blood transfusions and, if they have kidney failure, they may need hemodialysis.

People with the infection do not have to be isolated, but care must be taken when handling and disposing of their urine.

More Information

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

  1. Centers for Disease Control and Prevention (CDC): Leptospirosis: Comprehensive information about leptospirosis, including links for risk, prevention in people, and prevention in pets

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