KARACHI, Oct 19: The common cold grips the city as the swing between extreme temperatures becomes the widest in October. “October is the only month in the season which sees the greatest difference between the maximum and minimum temperatures. In Karachi, it also marks the onset of autumn, which is a transitory phase between summer and winter,” the director-general of the Pakistan Meteorological Department, Dr Qamaruzzaman Chaudhry, told Dawn.

In Karachi, the maximum and minimum temperatures were 39 degrees centigrade and 22.5 degrees centigrade, respectively, on Monday. Humidity stood at 26 per cent.

Astronomically, autumn begins with the autumn equinox in the Northern hemisphere and ends with the winter solstice.

However, meteorologists count the entire months of September, October and November in the Northern hemisphere as autumn.

“In Karachi’s case, the monsoon ends in mid-September. It is followed by a brief spell of autumn which soon gives way to winter,” explained Dr Chaudhry.

According to Dr Naseem Salahuddin, an expert of infectious diseases, the common cold becomes most active in cold and dry weather. “All sorts of respiratory tract diseases – such as flu, influenza and German measles – become widespread in cold and dry weather, especially in October, in Karachi. There are two reasons for the resurgence of respiratory tract diseases in this weather. One, mucosal lining of the respiratory dries up and all sorts of viruses enter the body easily. Two, people live in closed environment in this weather and transmit such diseases to one another,” she said.

Dr Salahuddin said the common cold, as well as other respiratory tract diseases, could be avoided by strictly following the principles of hygiene. She added that if people washed their hands on a regular basis and did not sneeze or cough into one another’s face, they could stop the common cold from spreading.