This possibly is the first indication of cluster formation of the virus, which means a large number of vulnerable children are at risk.

Last month, an outbreak of fever was reported in a private school hostel at Panchgani in Satara. After three weeks of the first report of flu, the National Institute of Virology (NIV) has started investigating the cases in Satara since July 23.

About 90 children were affected by influenza-like illness, which was first reported in the first week of July, official sources said. As many as 17 children were admitted to hospital. Twenty seven students of the school had been to the US to visit NASA and ten students had visited Holland in April and May resepctively.

When as many as 34 samples collected from the students were tested at NIV, ten were found positive for Swine flu virus, official sourced said.

In the last ten days, further samples were collected from other schools. Between July 26 and 29, as many as 127 samples were collected from six different schools in Panchgani. Twenty three samples from four different schools were tested positive. So far, 2,479 persons have been tested for H1N1, out of which 558 are positive.