Sydney, Aug 19 (IANS): New research adds to the growing body of evidence that low humidity, dry air can increase the risk of Covid-19 virus.

The study, published in the journal Transboundary and Emerging Diseases, focused on the Greater Sydney area during the early epidemic stage of Covid-19 found an association between lower humidity and an increase in community transmission.

"This second study adds to a growing body of evidence that humidity is a key factor in the spread of Covid-19," said study researcher Michael Ward from the University of Sydney in Australia.

The estimate is about a 2-fold increase in Covid-19 notifications for a 10 per cent drop in relative humidity.

According to the researchers, dry air appears to favour the spread of Covid-19, meaning time and place become important.

Accumulating evidence shows that climate is a factor in Covid-19 spread, raising the prospect of seasonal disease outbreaks.

The study revealed that reduced humidity was found in several different regions of Sydney to be consistently linked to increased cases. The same link was not found for other weather factors - rainfall, temperature or wind

Additional evidence from the Sydney Covid-19 epidemic has confirmed cases to be associated with humidity.

According to the researchers, there are biological reasons why humidity matters in the transmission of airborne viruses.

"When the humidity is lower, the air is drier and it makes the aerosols smaller," Ward said, adding that aerosols are smaller than droplets.

"When you sneeze and cough those smaller infectious aerosols can stay suspended in the air for longer. That increases the exposure for other people," he said

"When the air is humid and the aerosols are larger and heavier, they fall and hit surfaces quicker," Ward explained.

"This suggests the need for people to wear a mask, both to prevent infectious aerosols escaping into the air in the case of an infectious individual and exposure to infectious aerosols in the case of an uninfected individual," the study authors wrote.

Earlier, a study published in the Canadian Medical Association Journal, found that temperature and latitude are not associated with the spread of the Covid-19 disease.