That student in turn unwittingly passed it on to another 22 children in his school, forcing the authorities to shut the school.

According to Awate, an issue of concern for the authorities is that all the victims display very minor symptoms which are very difficult to diagnose and treat.

However, they have all been quarantined in the Naidu Hospital here, he added. The Mumbai victims are kept in quarantine at the Kasturba Hospital.

Unlike Pune, all the victims in Mumbai are adults who have a history of travel to and from major swine flu affected countries in Europe, South America and the US.

'We would like to emphasise that not a single case can be termed as serious. But we are taking maximum precautions since the virus is unknown and we want to prevent it from spreading,' Awate said.

All the 54 victims are expected to remain in hospital for periods ranging from a week to a fortnight.