Leptospirosis: The Flood-Related Disease You Should Know About

Leptospirosis is a bacterial infection caused by Leptospira bacteria. It is one of the most common waterborne diseases in tropical regions and sees a sharp increase after heavy rainfall and flooding. In recent years, countries in Southeast Asia have reported rising cases during and after the rainy season.

In 2025 and 2026, public health authorities across Southeast Asia warned of increased leptospirosis risk following severe flooding. The Department of Health in the Philippines reported a 38% increase in suspected cases, breaching epidemic thresholds. Health officials urged the public to seek immediate medical consultation after wading through floodwaters.

How Leptospirosis Spreads

Leptospira bacteria live in the urine of infected animals, particularly rats, but also dogs, cattle, and pigs. The bacteria survive in warm, fresh water and moist soil for weeks. When floodwaters rise, they spread the bacteria from animal urine into areas where people live, work, and play.

Humans become infected when contaminated water or soil comes into contact with:

• Cuts or breaks in the skin
• The eyes, nose, or mouth
• Mucous membranes

Walking, wading, or swimming in floodwater is the most common route of infection. The bacteria can penetrate intact skin if the exposure is prolonged, though broken skin offers an easier entry point.

Who Is at Highest Risk?

• People who walk or work in floodwater, even if the water is not deep
• Agricultural workers, farmers, and those handling contaminated soil
• Homeless individuals with no shelter from floodwater
• Rescue workers and volunteers clearing flood debris
• Children playing in flooded areas
• People living in areas with poor sanitation and rat infestations

Recognizing the Symptoms

Leptospirosis symptoms typically appear 2 to 30 days after exposure, most commonly within 5 to 14 days. The illness has two phases:

Early phase (first week):

• Sudden high fever
• Severe headache, especially in the forehead area
• Muscle aches, particularly in the calves and lower back
• Red eyes (without pus or discharge)
• Nausea, vomiting, or diarrhea
• Skin rash

Severe phase (in about 10% of cases):

• Jaundice (yellowing of the skin and eyes)
• Kidney failure
• Liver failure
• Bleeding, including from the lungs (pulmonary hemorrhage)
• Meningitis

The severe form, known as Weil disease, can be life-threatening. Without prompt treatment, the case fatality rate for severe leptospirosis can reach 10 to 40%. With early antibiotic treatment, most patients recover fully.

When to Seek Medical Care

If you have been exposed to floodwater or contaminated soil and develop any of the following symptoms, seek medical care immediately:

• Sudden fever after flood exposure
• Severe headache with muscle aches, especially calf pain
• Red eyes
• Yellowing of the skin or eyes
• Difficulty breathing

Tell your doctor about your flood exposure, which helps them recognize leptospirosis early, which significantly improves outcomes.

Diagnosis

Leptospirosis can be difficult to diagnose in its early stages because the symptoms resemble many other tropical infections, including dengue fever, malaria, and scrub typhus. Laboratory tests such as the microscopic agglutination test (MAT), PCR testing, and rapid diagnostic tests can confirm leptospirosis, but these are often not immediately available in rural or flooded areas.

Clinicians in endemic areas often treat suspected cases empirically based on the combination of symptoms and exposure history, without waiting for lab confirmation.

Treatment

Most cases of leptospirosis respond well to antibiotics when started early:

• Mild cases: oral doxycycline or amoxicillin
• Severe cases: intravenous penicillin or ceftriaxone

Antibiotics work best when given within the first 5 days of illness. In severe cases, supportive care in a hospital, including fluids, kidney dialysis, and respiratory support, may be necessary.

Prevention After Flooding

After heavy rain and flooding, follow these precautions:

• Avoid wading or swimming in floodwater. If you must enter floodwater, wear waterproof boots, gloves, and protective clothing
• Cover any cuts or wounds with waterproof dressings
• Avoid touching your face with unwashed hands
• Wash exposed skin thoroughly with clean water and soap as soon as possible after flood exposure
• Keep your living area clean and dry. Seal cracks and holes to prevent rats from entering
• Dispose of contaminated materials safely
• Store drinking water in clean, covered containers
• Boil or filter water if the supply may be contaminated
• Seek medical care promptly if symptoms develop

For people with high-risk exposure, such as agricultural workers or flood cleanup volunteers, preventive antibiotics may be considered. Doxycycline taken once weekly during high-risk periods can reduce the chance of infection, though this should be discussed with a doctor.

The Big Picture

Climate change is increasing the frequency and intensity of extreme weather events, including heavy rainfall and flooding. As flood-related leptospirosis cases are expected to rise in tropical and subtropical regions, communities must prepare with better early warning systems, rapid diagnostic capacity, and public education.

The key takeaway: leptospirosis is a serious but preventable disease. After flooding, stay out of the water when possible, cover your wounds, wash thoroughly if exposed, and seek medical care early if symptoms develop. Early treatment saves lives.