Pollen is tough enough for allergy sufferers, but a new study suggests it also helps spread the new coronavirus and other airborne germs.

Researchers had noticed a connection between COVID-19 infection rates and pollen concentrations on the National Allergy Map of the United States.

That led them to create a computer model of all the pollen-producing parts of a willow tree. They then simulated outdoor gatherings of 10 or 100 people — some of them shedding COVID-19 particles — and exposed the "crowd" to 10,000 pollen grains from the tree.

"One of the significant challenges is the re-creation of an utterly realistic environment of a mature willow tree," said study author Talib Dbouk, from the University of Nicosia in Cyprus. "This included thousands of tree leaves and pollen grain particles, hundreds of stems and a realistic gathering of a crowd of about 100 individuals at about 20 meters from the tree."

The researchers used the temperature, wind speed and humidity of a typical spring day in the United States and found that the tree's pollen passed through the crowd in less than one minute, which could significantly affect the virus load carried along with the pollen and increase the risk of infection.

The findings were published June 22 in the journal Physics of Fluids.

"To our knowledge, this is the first time we show through modeling and simulation how airborne pollen micrograins are transported in a light breeze, contributing to airborne virus transmission in crowds outdoors," study author Dimitris Drikakis, also from the University of Nicosia, said in a news release from the American Institute of Physics.

The investigators now plan to learn more about the mechanisms behind the interaction between airborne pollen grains and the human respiratory system under different environmental conditions.