Winter’s first chill may bring an unwelcome guest: flu outbreaks, a new study says.

Researchers looked at data on weather and flu cases in Gothenburg, Sweden, and found that flu outbreaks occurred about one week after the first stretch of cold weather and low humidity.

“According to our calculations, a cold week with an average temperature below zero degree Celsius [32 degrees Fahrenheit] precedes the start of the flu epidemic,” said study researcher Nicklas Sundell. He’s an infectious diseases specialist at Sahlgrenska University Hospital, which is affiliated with the University of Gothenburg.

“We believe that this sudden drop in temperature contributes to ‘kick-start’ the epidemic. Once the epidemic has started, it continues even if temperatures rise. Once people are sick and contagious, many more may become infected,” Sundell said in a university news release.

The findings support the theory that aerosol particles containing flu viruses and liquid spread more easily in cold and dry weather. If the surrounding air is dry, it absorbs moisture and the aerosol particles shrink and can remain airborne, the researchers said.

In northern regions of the world, cold weather is likely a more important factor in flu outbreaks than people crowding indoors during the winter, according to Sundell.

“But cold weather isn’t the only contributing factor. The virus has to be present among the population and there have to be enough people susceptible to the infection,” he said.

It’s also likely that weather plays a role in outbreaks of some other respiratory viruses as well, but not for cold-causing rhinoviruses, the researchers said.

“If you can predict the start of the annual epidemics of the flu and other respiratory viruses, you can use this knowledge to promote campaigns for the flu vaccine and prepare emergency wards and hospital staff in advance for an increased number of patients seeking care,” Sundell said.

He added that the recommendations to try to prevent the flu are the same as in previous years. Get a flu vaccine, cough and sneeze into your elbow, and remember to wash your hands.

More information

The U.S. Centers for Disease Control and Prevention has more on the flu.

Source: HealthDay