Detection of about 12 Swine flu cases in the last fortnight has put the health authorities here on an alert, as two patients are reported to be in a critical condition.

While some of the cases have been detected in a "pro-active" research survey, undertaken by the city-based National Institute of Virology (NIV) in a locality here, other non-specified areas, too, have reported H1N1 infections.

"While the cases detected by NIV are being treated as outdoor patients without admission, other cases, which include two critical ones, call for a greater surveillance, as Pune had not reported any fatality on account of Swine flu in the last year," Dr Pradip Awate, State swine flu surveillance officer said.

Two of the three critical patients, admitted to ICU in different hospitals, were put on ventilator, health officials said.

General practitioners, treating seasonal influenza cases, have been advised to screen patients for suspected H1N1 infections, they added.

Pune became the epicentre of swine flu cases since recording the first fatality of the dreaded infection in 2009, leading to vigorous surveillance measures that saw a substantial reduction in its transmission.