An "epidemic" of cold, cough and fever is sweeping across the city aided by frequent temperature fluctuations, doctors said.

A doctor at a government medical college in Calcutta said about 20 per cent of the patients visiting OPDs (outpatient departments) are complaining of cold, cough and fever.

Such infections are common at the onset of winter and again when winter recedes and the Celsius starts rising, doctors said. Most patients are recovering within three or four days but doctors are advising medical consultation if the fever persists beyond that.

"This (the ongoing spell of illness) has assumed proportions of an epidemic. About 20 per cent of the patients visiting the OPD are complaining of fever and associated symptoms," said Soumitra Ghosh, the head of the general medicine department at Medical College Kolkata.

"The most common symptoms are fever, runny nose, cough, muscle and joint pain and sore throat," said Ghosh.

The infections are impacting people across age groups, doctors said.

Yogiraj Ray, the head of the infectious disease department at SSKM Hospital, said the number of patients at the OPDs with such complaints has increased sharply. He, however, said no one is requiring hospital admission.

Ray said the temperature fluctuations are resulting in a "shift in the population of viruses", which could be the reason for so many people getting infected. Dust, too, might be a contributing factor, he said.

Prabhas Prasun Giri, a paediatrician at the Institute of Child Health, said many patients coming to his clinic are suffering from cough, cold and fever.

"This usually happens when winter recedes and the temperature goes up. Such infections are common around November and February. Fever, cough, congestion and body ache are among the commonest symptoms," said Giri.

Chandramouli Bhattacharya, an infectious disease specialist at Peerless Hospital, said that while other symptoms subside in a few days, the cough persists a little longer.

"I would say the current spell of fever, cold and cough has been going on for quite some time and has not subsided yet. While all other symptoms are receding faster, the cough is continuing for a longer period," he said.

Most patients are not being advised any test unless the illness persists or becomes severe.

Paediatrician Giri said the few tests performed on the children returned positive for the parainfluenza virus and the rhinovirus.

A 19-year-old resident of Gariahat has been down with a fever, and also suffering from sore throat and body ache, for three days.

"When she went to college to attend an important class, she learnt that many of her classmates had been down with similar symptoms," the student's father said.

The warm weather in the afternoon is forcing many to switch on the air-conditioner during the daytime. A south Calcutta resident said he goes to bed at night switching on the fan but a brief nip in the air forces him to switch it off at dawn.