An outbreak of a new viral infection referred to as tomato flu that was first detected in children in the southern Indian state of Kerala in May has spread to two other states.

According to an article in the Lancet Respiratory Medicine, 82 children aged under five had been diagnosed with the virus in Kerala as of 26 July.

Cases have now been reported in neighbouring Tamil Nadu state and in Odisha in the east, where children as old as nine have been infected, even though the virus usually affects under-fives.

Scientists are still trying to identify exactly what this virus is. It has been referred to as tomato flu because of the painful red blisters it produces on the body, and it is very contagious. Children are particularly vulnerable because it spreads easily through close contact, such as via nappies, touching unclean surfaces or putting things in mouths.

“The rare viral infection is in an endemic state and is considered non-life-threatening; however, because of the dreadful experience of the Covid-19 pandemic, vigilant management is desirable to prevent further outbreaks,” the Lancet article said.

Doctors say diagnosing tomato flu is difficult because its symptoms are very similar to those of Covid, chikungunya and dengue fever. The latter two are common in India during the rainy season and are spread by mosquitoes. Chikungunya is particularly widespread in Kerala.

The Lancet article says tomato flu could be an after-effect of chikungunya or dengue fever in children rather than a viral infection.

It adds: “The virus could also be a new variant of the viral hand, foot and mouth disease, a common infectious disease targeting mostly children aged one to five years and immunocompromised adults, and some case studies have even shown hand, foot and mouth disease in immunocompetent adults.”

Dr Suneela Garg, a senior health official in the Delhi government, said: “I agree that chikingunya and dengue can leave children vulnerable to tomato flu because their immune systems are weaker. We don’t have any cases in Delhi yet and I am confident it won’t become a problem.”

The spread of tomato flu comes as India has recorded a steady rise in Covid cases in the past few weeks, along with cases of swine flu.

Prof Dileep Mavalankar, of the Institute of Public Health in Gandhinagar, said: “Swine flu had declined during Covid but it is now on the rise again in the big cities. But because the test for it is expensive, few people get tested for it so the numbers are unclear.”