Almost 200 cases of leptospirosis, a waterborne disease known locally as ‘rat fever’, have been confirmed in Kerala, a health ministry spokesman said.
The number of dead is officially confirmed at nine, but is expected to rise to 40 pending medical reporting.
A health specialist claims 30 people have died in the past week.
Mohammed Javeed, internal medicine specialist at a private hospital in Kerala, said: “In the past week, we have seen about 30 deaths in Kozhikode and Wayana.”
The districts are two of the worst-flooded on India’s southwest coast.
Mr Javeed said the region sees rat fever cases every monsoon season.
When paddy fields fill with water, farmers are at risk of catching ‘rat fever’ which is transmitted via the urine of infected animals.
But this time he says the scale of the outbreak is particularly alarming as patients don’t have usual symptoms such as mild jaundice, blood in urine or bleeding spots on the skin.
He told Reuters: “This time it is a fast, progressive infection.
“The recent deaths indicate clearly the threat of an epidemic.”
The surge in cases comes after torrential rain beginning on Aug. 8 flooded almost the entire state, killing hundreds of people, destroying thousands of homes and causing at least 200 billion rupees (£2.18 billion) worth of damage.
Health Minister K.K. Shailaja told reporters the health ministry were distributing preventive medicine and warned of other waterborne diseases such as typhoid and cholera.
Responding to local media reports of three leptospirosis deaths today, the minister said: “The victims had unfortunately not taken preventive medicine.”
Leptospirosis rarely spreads from person to person and can be treated with common antibiotics.
People with wounds or cuts are more likely to catch the disease and are advised to avoid contact stagnant or contaminated water.
Kerala, which has 44 rivers, witnessed its worst floods in 1924 following torrential rains.