We all know that the influenza virus is spread by airborne droplets. This can be directly when a sick person coughed or sneezed, and a healthy person standing next to him inhaled air containing the virus; by means of an aerosol or droplets formed during sneezing and coughing and containing vibrios (virus particles); or due to direct contact with the patient's secretions. However, scientists still do not know how the flu spreads.
Researchers from the University of Maryland, led by Professor Donald Milton, decided to find out whether the influenza virus can spread not only through coughing or sneezing, but simply through the breathing of a sick person. Scientists shared about their work in the journal Proceedings of the National Academy of Sciences.
From December 2012 to March 2013, doctors and biologists monitored 355 volunteers, students aged 19 to 22 years, who had symptoms of ARVI. 142 of them were diagnosed with the flu, and the rest (healthy) did not take part in the experiments. Each participant in the experiment underwent a procedure for taking samples from the nasopharynx. On the fourth day after the onset of symptoms of the disease, breath samples were taken from people. The person was asked to breathe in a special device that collects aerosols for 30 minutes. During this half hour, large (with a diameter of more than 5 micrometers) and small (less than 5 micrometers, but more than 50 nanometers) droplets of exhaled aerosol were collected inside the device. As a result, scientists collected a total of 218 samples from the nasopharynx, as well as breath samples. Then the scientists analyzed the samples and various aerosol fractions for the presence of viral RNA. Besides,To test viable viruses in the secretions of patients, the authors of the work grew viral cultures on model cells of canine kidneys.
In fact, it turned out that viral RNA was contained in 97 percent of samples from the upper respiratory tract, in 76 percent - from the "fine" aerosol fraction (with small droplets) and 40 percent of the samples in the "coarse" fraction. Viable viruses were found in 89 percent of nasopharyngeal samples and 39 percent of fine aerosolized samples. In their article, the researchers note that vibrios were found in half of the breath samples from people who did not cough or sneeze during the experiment. From this we can conclude that the droplets when exhaled were not formed as a result of sneezing or coughing, but with the help of another mechanism. The authors of the work suggested that tiny droplets are formed in the lungs during the expansion and contraction of the bronchioles and go out with exhalation.
Nikolay Khizhnyak
