Fever After Walking Through Chennai Floodwater: When It Could Be Leptospirosis

Fever that begins 2 to 30 days after contact with flood water, stagnant water, sewage or wet mud can be leptospirosis. The usual gap is 5 to 14 days (National Guidelines on Leptospirosis, NCDC, MoHFW, 2015). Anyone in Chennai who waded through water, cleaned a drain or walked barefoot in the past month and now has fever with severe muscle pain needs to be seen and tested.

That 30-day tail is the whole point. A patient in Egmore, Chennai often does not connect a fever today with a flooded street three weeks ago, so the exposure never gets mentioned and the diagnosis never gets considered. The exposure history is not an optional extra. It is part of the national case definition (NCDC, MoHFW, 2015).

One thing before anything else. AJSMC is an outpatient and day-care multi-specialty centre in Egmore, Chennai, open Monday to Saturday, 10am to 9pm. It has no casualty unit, no trauma unit, no inpatient beds, no intensive care, no dialysis and no 24-hour emergency department. Severe leptospirosis is an inpatient illness. If someone with fever has yellowing of the eyes or skin, has stopped passing urine or is passing very little, is breathless, is coughing blood, is bleeding, or is confused or drowsy, do not come to an outpatient clinic and do not wait for the next outpatient session. Call 108 or go straight to the nearest hospital with a 24-hour emergency department and intensive care.

Is leptospirosis caught from a rat bite?

No. The Tamil name for it translates as rat fever, and that name misleads people into ruling themselves out because no rat ever bit them. The organism enters through abraded skin or through the mucous membranes of the eyes, nose and mouth in contact with an environment contaminated by the urine of rodents or other carrier animals (NCDC, MoHFW, 2015). Direct person-to-person spread is rare.

The Chennai mechanism is specific and worth understanding. Rodents and cattle excrete large numbers of the organism in their urine into soil and water. When an area waterlogs, rodents are forced out of their burrows and contaminate the standing water they are driven into (NCDC, MoHFW, 2015). Four rodent species are established reservoirs in India: the house rat, the Norway rat, and the lesser and larger bandicoots. A flooded Chennai street is therefore a transmission site, and a graze on the ankle is enough of a doorway.

Which exposures in the last month actually count?

More than most people in Chennai assume. The list below is NCDC's own, and two entries on it — lorry drivers and masons — are the exposures that get missed in a city, because neither person thinks of themselves as doing wet outdoor work.

Do not narrow this to farmers or to young men. In Tamil Nadu's own surveillance, the mean age of confirmed cases was 35 years, 66.1% were aged 20 to 60, and females made up 50.18% of cases against 49.78% males (Tamil Nadu Journal of Public Health and Medical Research, Vol 4 Issue 2, April–June 2024). Chennai is the state's highest-burden district. A homemaker who crossed a flooded lane to buy milk is inside this list.

What are the first symptoms of rat fever?

Fever with chills, and muscle pain that is out of proportion to everything else. NCDC calls myalgia a characteristic finding: the calf, abdominal and lumbosacral muscles are very painful and severely tender, and the guideline states plainly that this symptom is very useful in differentiating leptospirosis from other causes of fever. It is usually accompanied by a rise in serum creatine phosphokinase (CPK), which further helps separate it.

Two cautions about that table. Red eyes are not present in every patient, and their absence does not exclude leptospirosis — treat them as a strong clue when present, not as a filter. And the last row is the single most useful thing a patient in Chennai can know: NCDC states that all the clinical features either decrease or disappear within two to three days and then reappear and may progress to severe disease. Levett (Clinical Microbiology Reviews, 2001) describes the same two-part course, an acute phase of about a week, then an immune phase. Feeling better on day 3 is not recovery. Every year people stop the follow-up appointment at exactly that point.

Is calf pain with fever enough to get tested in Chennai?

Yes. NCDC's operational rule is unambiguous: in an endemic area, all cases of fever with myalgia and conjunctival suffusion should be considered suspected cases of leptospirosis (NCDC, MoHFW, 2015). The same document names Chennai city among the high-burden areas of Tamil Nadu, so this city meets the endemic-area condition. Tamil Nadu's Health Department fever advisory of 12 August 2026 lists leptospirosis first among the rainy-season illnesses and names severe muscle pain and red eyes in its own symptom list, telling the public to consult a doctor and undergo medical examination instead of self-medicating.

The full national suspected-case definition is acute fever with headache, muscle pain and prostration, together with a history of exposure to infected animals or to an environment contaminated with animal urine, plus one or more of: calf muscle tenderness; red eyes; passing little or no urine, or protein in the urine; jaundice; bleeding; neck stiffness; or nausea, vomiting, abdominal pain and diarrhoea. Notice that the exposure sits inside the definition. Bring it up at the consultation even if nobody asks.

Telling leptospirosis apart from dengue, typhoid and chikungunya is a separate question, and it is covered in detail in the AJSMC article on monsoon fever in Chennai. One point belongs here though: NCDC lists falciparum malaria, dengue, scrub typhus, typhoid and viral hepatitis as illnesses that closely resemble leptospirosis, and adds that the possibility of co-infection should be kept in mind. A confirmed dengue does not rule out a simultaneous leptospirosis.

Can a leptospirosis test be negative when you actually have it?

Yes, and the commonest reason is the day it was taken. Antibodies become detectable in the blood only about 5 to 7 days after symptoms start (Levett, Clinical Microbiology Reviews, 2001). A negative antibody test on day 2 or day 3 of fever is uninformative, not reassuring.

Three practical consequences for a patient in Egmore, Chennai. Write down the date the fever started and take it to the consultation. It decides which test is worth sending. Do not take an antibiotic before a blood culture is drawn, because the sample must be collected before antibiotics are started. And if the first test was negative and the fever continues or returns, go back; a repeat sample later in the illness is often what makes the diagnosis.

Supporting blood tests do not diagnose leptospirosis, but they tell a doctor how the illness is behaving. NCDC lists what a general laboratory may show: mildly raised white cell count with neutrophilia, ESR around 60 mm, low platelets, raised blood urea and serum creatinine, protein and blood and casts in the urine, raised bilirubin, and marked elevation of CPK. One correction matters for readers used to dengue content — the platelet count is not the number to watch here. NCDC states that bleeding in leptospirosis is not directly related to the level of thrombocytopenia.

Which signs mean this needs a hospital and not an outpatient clinic?

Any one of the signs in the table below. NCDC's instruction is that these patients are shifted to a higher centre immediately, whether the rapid test is positive or negative.

The reason for the urgency is in the numbers. About 90% of patients have the milder anicteric form — fever and muscle pain without jaundice, and about 5 to 10% have the icteric form with jaundice and organ involvement, which is Weil's disease. Case fatality across leptospirosis runs from 0 to 15%, and icteric disease carries a mortality of 5 to 15% (NCDC 2015; Levett, 2001). More than 90% of deaths are from bleeding into the lungs and from kidney complications, and NCDC states that death can occur within hours to two days from pulmonary haemorrhage and severe respiratory distress. Jaundice, when it comes, starts after 4 to 7 days of illness. Leptospirosis in pregnancy carries a poor prognosis, with high foetal loss reported in the first trimester and near term.

Every requirement in that right-hand column is something AJSMC does not have. The honest role of an outpatient centre in Egmore, Chennai is suspicion, examination, baseline tests and early referral, never the treatment of severe leptospirosis.

Should I take an antibiotic after wading through flood water?

Not on your own, and not on a chemist's advice. A preventive antibiotic course after exposure is a public-health measure, not a personal one: the national guideline directs it at defined occupational groups in endemic areas where a health authority has identified a cluster of cases, during the peak transmission season, for a fixed period of six weeks that is never to be extended beyond eight (NCDC, MoHFW, 2015). Nothing in that describes an individual who walked through water last Tuesday.

The evidence behind it is also weaker than the confidence with which it is repeated. The Cochrane review of antibiotic prophylaxis for leptospirosis (Win TZ and colleagues, Cochrane Database of Systematic Reviews, 2024, CD014959.pub2) examined five randomised trials with 2,593 participants across Brazil, Sri Lanka, India, Panama and Iran, with evidence current to April 2023. It concluded that there is insufficient evidence to support or refute antibiotic prophylaxis: antibiotics may make little to no difference to the clinical diagnosis of leptospirosis and little to no difference to deaths from any cause, and may increase non-serious side effects such as diarrhoea, nausea and vomiting.

Treatment of a suspected or confirmed case is a different matter, and it is a doctor's decision made after examination. This article names no antibiotic, no dose and no duration, deliberately. A self-started antibiotic before a blood sample is drawn can also destroy the chance of a culture-confirmed diagnosis.

What is safe to take for the fever and the muscle pain?

Less than people assume, which is why the advice here is to be examined rather than to be medicated. Two specific warnings apply to leptospirosis and both are counter-intuitive.

• Do not take ibuprofen, diclofenac, nimesulide, mefenamic acid or any similar painkiller for the muscle pain. NSAIDs are named among the drugs to avoid where there is kidney involvement (NICD/DGHS, 2006), and kidney involvement is almost invariable in leptospirosis (NCDC, 2015). These are exactly the tablets an aching-calves patient reaches for.
• If the eyes or skin have turned yellow, or the urine is dark, stop self-medicating entirely and get tested before taking anything. Paracetamol is listed among the drugs to avoid where the liver is involved in leptospirosis (NICD/DGHS, 2006), and jaundice in the severe form starts from day 4 to 7 of illness.
• There is no home treatment for leptospirosis. No decoction, herbal preparation or kitchen remedy prevents it after exposure or treats it once it starts. Tamil Nadu's Health Department advisory of 12 August 2026 tells the public to consult a doctor and undergo medical examination instead of self-medicating, and that is the correct instruction.

How common is leptospirosis in Chennai?

Common enough that Chennai alone accounts for over a third of the whole state's confirmed cases. The figures below come from the Tamil Nadu Directorate of Public Health and Preventive Medicine's own analysis of IDSP-IHIP surveillance data, and from Ministry of Health figures tabled in the Rajya Sabha.

Read the 2026 figure with its date attached. The 1,473 cases cover January to June only, and the state's own seasonal analysis shows cases climbing from June through to December. Publishing in mid-August places Chennai on the rising limb of the curve, not past it. This is not an outbreak. It is the season.

The 63.6% hospitalisation figure deserves separate attention, because it corrects a comfortable misreading. About 90% of leptospirosis is the milder clinical form, but that describes the form of the illness, not the setting it is safely managed in. Nearly two out of three confirmed cases in Tamil Nadu needed a hospital bed.

What actually prevents leptospirosis during the Chennai monsoon?

Physical barriers and skin care, before and after exposure. This is NCDC's own list, taken from the national guideline and its public-facing prevention poster, whose headline is that early reporting to a health facility can prevent illness and death.

For a household in Egmore, Chennai the practical version is short: keep a pair of rubber boots by the door through the monsoon, cover any cut on the foot or leg before going out into water, wash and dry the feet with soap the moment you are back indoors, and keep food and grain in closed containers so rats have no reason to be in the building.

What can AJSMC in Egmore do about this, and what can it not?

What an outpatient centre can usefully do is see a febrile patient early, take the exposure history properly, examine for the separators, send baseline blood and urine tests, and refer without delay if any of the warning signs above are present. AJSMC has an in-house laboratory in Egmore, Chennai handling blood and urine samples, and outpatient consultations in General Medicine run Monday to Saturday, 10am to 9pm.

Confirmatory leptospirosis testing — IgM ELISA, MAT, PCR and culture — is specialised serology. Before travelling for a test, call 044 2532 2021 and ask which of the tests named in this article can be run in-house and which are sent to a referral laboratory, and by what time in the day a sample has to be given. Sending a sample to the wrong place wastes the very day of illness this article is about.

What AJSMC cannot do is treat severe leptospirosis, and no patient should be brought here for it. Dialysis, oxygen, mechanical ventilation, blood-pressure support and cardiac monitoring are what severe disease needs, and AJSMC has no inpatient beds, no intensive care, no dialysis and no 24-hour emergency department. Outside 10am to 9pm, and on Sundays, there is no outpatient service here at all, which matters in an illness where lung bleeding can kill within hours to two days. For those patients the destination is a hospital with a 24-hour emergency department, reached by calling 108 if needed.

When should you see a doctor?

See a doctor for any fever that starts within a month of contact with flood water, stagnant water, sewage, wet mud, farm work or animals, and say so at the consultation, even if nobody asks. Come sooner if the fever comes with severe calf, thigh or lower-back muscle pain, an intense headache that painkillers do not touch, or redness of both eyes without discharge. Come back if the fever settles for two or three days and then returns, because that is the pattern of this illness and not the end of it.

Go to a hospital with a 24-hour emergency department instead, or call 108, if there is yellowing of the eyes or skin, reduced or absent urine, breathlessness, blood in the cough, any bleeding, confusion or drowsiness, or cold hands and feet. Those are NCDC's own immediate-referral criteria, and they apply whether a rapid test has come back positive or negative.

Take the date the fever started and the date of the water exposure with you. Between them, those two dates decide which test is worth sending and how it should be read.