Medical experts have recognized for some time that people become infected with flu during the winter months.But they did not really know why until recently.
American researchers say they now know why the flu virus spreads in the winter and not in the summer.They say it is because the virus remains in the air longer when the air is cold and dry.
Researchers in New York carried out twenty experiments with guinea pigs to investigate how the virus spreads.The researchers found the virus spread the most when the temperature was about five degrees Celsius and the humidity was twenty percent.Few of the guinea pigs developed flu as the temperature increased.The virus stopped spreading completely at thirty degrees Celsius and eighty percent humidity.The researchers also found that the animals spread the virus among themselves nearly two days longer when the temperature was low.
One of the researchers said the study shows that flu virus is more likely to infect people during an outdoor walk on a cold day than in a warm room.He said cold air helps the virus survive in the air and low humidity helps it stay there longer.That is because particles of the virus ride on the extremely small drops of water floating in the air.When the air is very humid,water droplets fall to the ground more quickly.
The researchers say,however,that people should not stay in warm places all the time in cold weather to avoid the flu.They say the best way to prevent the sickness is to get yearly injections of a vaccine that prevents flu.
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