Leptospirosis: the tropical infection that’s easy to miss

Leptospirosis is a bacterial disease caused by Leptospira species. These spiral-shaped bacteria live in the kidneys of animals and are shed in urine. People become infected when water or soil contaminated by those bacteria touches broken skin or mucous membranes.

It occurs worldwide but is most common in tropical and subtropical regions, especially after heavy rains or flooding. Globally, about one million people get leptospirosis, and the infection is linked to 60,000 deaths.

Leptospirosis outbreaks often follow heavy rains or floods, especially in areas with poor sanitation and many rodents. Even popular travel destinations have reported cases: for example, leptospirosis spikes have been noted after flooding in Hawaii and Puerto Rico.

Travelers, outdoor enthusiasts, and people in certain occupations are at increased risk.

People who swim, raft, or kayak in fresh water (especially after heavy rain) are at high risk. Those who hike in wet fields, or work with livestock or rodents in endemic areas, are also at risk.

Leptospirosis can cause anything from a mild flu-like illness to severe organ failure.

Common signs of leptospirosis include:

• Fever
• Headache
• Chills
• Muscle or body aches
• Vomiting, nausea, diarrhea, or abdominal pain
• Jaundice (yellowing of the skin or eyes)
• Red or bloodshot eyes (conjunctival suffusion)
• Rash

Symptoms usually start about 5–14 days after exposure to the bacteria.

Early illness can feel like a bad flu, but leptospirosis can worsen without treatment. An untreated leptospirosis infection may progress to serious complications involving multiple organ systems (Weil’s syndrome). This can include kidney or liver failure, meningitis, or respiratory distress.

Respiratory distress causes very rapid, labored breathing and low oxygen levels in the blood. In leptospirosis, respiratory distress can occur if the bacteria severely affect the lungs. This is a medical emergency and may require oxygen support or even a ventilator.

Leptospirosis is notoriously difficult to diagnose early because its symptoms are so general.

Fever, headache, and body aches resemble dozens of other illnesses. There is usually no rash, and red eyes can look like simple conjunctivitis.

Even lab tests can be confusing. During the first week of illness, only culture or PCR of blood will detect Leptospira (because the bacteria are present in the blood then). Antibody tests (IgM ELISA or the microscopic agglutination test) become positive later.

In practice, a doctor might test too early and get a false-negative, or wait too long and lose the chance to confirm quickly.

Because leptospirosis mimics so many diseases, it is frequently labeled as something else first. In the tropics, clinicians commonly assume fever and aches are dengue, malaria, typhoid, or influenza.

Viral infections like chikungunya or hepatitis, and bacterial infections like rickettsial fevers, can present very similarly. Even life-threatening conditions (meningitis, sepsis) can look alike initially.

In short, if doctors don’t explicitly suspect leptospirosis, they may treat the more common diseases by default.

A detailed exposure history is often the key.

Doctors should ask their patients about recent travel and activities involving water and animals:

• Has the person traveled to or lived in a region known for leptospirosis?
• Did they swim, wade, raft, or have contact with potentially contaminated water?
• Did they work with animals or rodents that could carry the bacteria?

Symptoms like conjunctival redness and calf muscle tenderness support the diagnosis, especially if routine labs show kidney or liver abnormalities.

If leptospirosis is on the differential, a blood sample can be sent for Leptospira PCR (usually positive only in the first week) and later for serology (IgM ELISA).

In general, a positive PCR or a high antibody titer on paired sera provides a definitive diagnosis. Since waiting for confirmation can be risky, doctors usually start antibiotics (for example, doxycycline, amoxicillin, or ceftriaxone) if they suspect leptospirosis.

Early therapy also improves outcomes.

In well-equipped settings, diagnosis combines history with lab testing:

• PCR testing of blood (in early illness) or urine (after the first week) detects Leptospira A positive result confirms infection. It’s fast and useful in the first week of illness
• Serologic tests, such as IgM ELISA, can screen for antibodies. But these may not become positive until after the first week. Results must often be confirmed with the microscopic agglutination test (MAT)
• The culture of the organism is rarely used. It’s slow, has low sensitivity, and isn’t practical for clinical diagnosis

In this setting, confirming leptospirosis is straightforward: a positive PCR or a rise in MAT titer clinches the diagnosis. When leptospirosis is confirmed by these tests, other diagnoses are largely ruled out.

By contrast, in resource-poor clinics, most of those tools are missing. Doctors can then rely on clinical patterns and basic labs.

A validated diagnostic scoring model in Sri Lanka found key predictors, including

• Exposure history
• Elevated creatinine
• Neutrophil dominance
• High bilirubin
• Low platelets

When test confirmation isn’t possible, clinicians often begin antibiotic treatment when the clinical picture strongly suggests leptospirosis.

For instance, in a flood-prone area, a patient with fever who has both kidney impairment (high creatinine) and liver involvement (elevated bilirubin) – and a history of wading through water – might be treated presumptively for leptospirosis.

Treatment should begin as early as possible (ideally before lab confirmation) to reduce the risk of severe disease.

• Mild disease: Oral doxycycline (except in pregnancy and children under 8 years) or amoxicillin
• Severe disease: Intravenous penicillin G or third-generation cephalosporins (e.g., ceftriaxone, cefotaxime)
• Supportive care may include intravenous fluids, dialysis for kidney failure, and respiratory support

Prevention focuses on avoiding exposure and, in some cases, taking prophylactic antibiotics.

• Avoid swimming or wading in freshwater streams, rivers, or floodwaters that may be contaminated, especially after heavy rains in endemic areas.
• Wear protective clothing and footwear when working in wet or muddy conditions.
• Control rodents around homes, farms, and workplaces.

For travelers with unavoidable high-risk exposure (e.g., adventure races, military exercises), weekly doxycycline prophylaxis (200 mg) can be considered.

Leptospirosis is a classic “don’t miss” diagnosis in the tropics. Its flu-like presentation and wide-ranging symptoms make it easy to overlook, especially if doctors aren’t thinking of it.

The challenge is to put together the clues: travel or freshwater exposure in an endemic area, the combination of muscle pains and organ findings, and abnormal labs.

In well-equipped settings, PCR and serology can confirm the diagnosis. In low-resource settings, a high index of suspicion can prompt early treatment. In every case, remembering leptospirosis as part of a differential diagnosis and acting quickly can make the difference in patient outcomes.

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