Manifestation of epidemic process, clinical and epidemiological characteristics of adult patients in the early period of the COVID-19 epidemic in Russia

Aims: to study the epidemic process, clinical and epidemiological features of adult patients with COVID-19 identified during the first and second periods of the rise and decline in the incidence of new coronavirus infection in Russia. Materials and methods: this study included patients aged ≥18 years with a confirmed diagnosis of COVID-19, identified in the periods from 03/02/2020 to 30/06/2020 (n=286 205) and from 11/01/2020 to 01/31/2021 (n=1 655 022) in Russia. Results: at the early stage of the COVID-19 epidemic in Russia, there were defined 2 periods of rise and fall in incidence: March - August 2020 and September 2020 - May 2021. The median age of patients with COVID-19 in the first period was 50.0 [37- 62] years, in the second – 52.0 [39-64] years. The share of females was 55.5% and 60.1%, respectively. The distribution of patients in the first and second periods was: mild - 63.0% and 74.4%, moderate - 29.0% and 20.1%, severe - 4.9% and 3.5%, extremely severe – 3.1% and 2.1%, respectively. In the first period, the structure of cases was dominated by people in the age group 50-59 years (20.5%), in the second - 60-69 years old (20.5%). The median duration of the period from the onset of symptoms to diagnosis was 4 days in both periods, of the disease was 16.0 [12-21] and 13 [10-17], of hospitalization was 15.0 [12-20] and 13.0 [10-18]. The rate of hospitalizations was 48.4% and 25.6% in the first and second periods, rate of transfers to the ICU - 7.8% and 10.3%, IMV - 5.6% and 7.7%, respectively. In both periods, the median age of the deceased was 73 [66-82] years, with a higher proportion of men in all age groups except 18-29 and 70+ years. One or more chronic diseases, male gender increased the likelihood of death (OR=10.2 and OR=1.3 in the first period; OR=16.0 and OR=1.6 in the second, respectively). Conclusions: in the early period of the COVID-19 epidemic in Russia, related to the spread of the “wild” strain of SARS-COV-2 and genetically closely related lines, differences in the manifestations of the epidemic process and clinical and epidemiological characteristics of patients were revealed. In the second period there was a decrease in the frequency of the heavy and extremely severe COVID-19, a decrease in the frequency and duration of hospitalizations, but a slight increase in the frequency of ICU and IMV was noted.