A 10-year-old in Mumbai walks home from school through a waterlogged lane, with dirty rainwater reaching his ankles. The water has mixed with runoff from an overflowing drain.

For the next two weeks, he seems perfectly fine.

Then comes a fever, followed by body ache and a headache. His parents assume it is one of the viral infections that often go around during the monsoon.

When the fever refuses to settle, a doctor asks them one important question: Did he walk or play in dirty rainwater recently?

That small detail can completely change what the doctor looks for.

During Mumbai’s monsoon, doctors are watching closely for leptospirosis, a bacterial infection that people can pick up after coming into contact with water contaminated by the urine of infected rats, cattle or dogs.

For parents, the tricky part is that a child may fall sick several days after playing in puddles or walking through a waterlogged street. By then, the rainwater they came into contact with may be the last thing anyone remembers.

Dr Amol Jaybhaye, Consultant in Infectious Diseases at Narayana Health SRCC Children's Hospital, says Mumbai has already seen more leptospirosis cases this year compared with the same period in previous years.

Children can be particularly vulnerable because they are more likely to splash through puddles, play in stagnant water or walk barefoot during the rains.

The Brihanmumbai Municipal Corporation's Epidemiology Cell data also shows why doctors take the infection seriously.

Among suspected........

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