Researchers from Hong Kong and Guangzhou universities found that patients with coronavirus infection COVID-19 can begin to transmit the virus for two or three days before the first symptoms. Article with the results of the authors published in the journal Nature Medicine.
On the effectiveness of control measures aimed at preventing the spread of SARS-CoV-2, can be affected by several factors. Among them, the time between similar phases of infection in cases of (serial interval) and the period between exposure and onset of symptoms (incubation period). If the serial interval is shorter than the incubation period, this may indicate that the transmission occurred before the appearance of obvious symptoms. In the result of control measures being taken at the time of the onset of symptoms may be less effective in combating the spread of infection.
The authors of the new study collected swabs from the throat in 94 patients with COVID-19, admitted to the eighth people’s hospital Guangzhou in China. Samples were collected from the onset of the first symptoms and then several times during the month. As a result, the researchers received 414 smears, which are then analyzed together with data on the symptoms and the linkage of events in time. Scientists have measured the concentration of the virus and found that the highest viral load was in patients in the early symptoms of the disease.
After this, the researchers turned to another sample, taken from publicly available data. It contained the results of the analyses 77 pairs of patients, one of whom is likely infected the other. Based on these measurements scientists were able to make a picture transmission COVID-19 from person to person. It turned out that the person becomes infectious for two to three days before symptoms appear, and its danger as a carrier of the disease reaches its peak in the 0.7 days prior to their appearance. The authors estimate that 44% of secondary cases of infection COVID-19 was obtained during presentano stage. The infectivity of a person, according to forecasts, decreases rapidly for seven days.
