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

BACKGROUND: The COVID-19 pandemic became a challenge and caused significant social and economic damage to most countries. For the most objective assessment of the epidemiological and clinical features of COVID-19 during different periods of the epidemic, studies based on a large volume of data on patients identified throughout the Russian Federation are necessary. AIM: To analyze the epidemic process and 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 COVID-19 in Russia. MATERIALS AND METHODS: This study included patients aged ≥18 years with a confirmed diagnosis of COVID-19 and identified in the periods from March 2, 2020, to June 30, 2020 (n=286,205) and from November 1, 2020, to January 31, 2021 (n=1 655 022), in Russia. RESULTS: At the early stage of the COVID-19 epidemic in Russia, two periods of the rise and fall in incidence were noted: March–August 2020 and September 2020–May 2021, using the Wald–Wolfowitz test. The median age of the patients with COVID-19 in the first and second periods were 50.0 37–62 and 52.0 39–64 years, respectively, and women accounted for 55.5 and 60.1% of the patients, respectively. The distributions of patients according to disease severity in the first and second periods were as follows: 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 and second periods, cases were dominated by patients aged 50–59 years (20.5%) and 60–69 years (20.5%), respectively. In both periods, the median duration from the onset of symptoms to diagnosis was 4 days, the median disease durations were 16.0 12–21 and 13 10–17, and the median duration of hospitalization were 15.0 12–20 and 13.0 10–18. The hospitalization rates were 48.4 and 25.6% in the first and second periods; transfer rates to the ICU, 7.8 and 10.3%; and invasive mechanical ventilation rates, 5.6 and 7.7%, respectively. In both periods, the median age at death was 73 66–82 years, with a higher proportion of men aged 30–39, 40–49, 50–59, and 60–69 years. The presence of one or more chronic diseases, as well as male sex, increased the likelihood of death (odds ratio = 10.2 and 1.3 in the first period; odds ratio = 16.0 and 1.6 in the second period). 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 variants, the manifestations of the epidemic process and clinical and epidemiological characteristics of patients varied. In the second period with higher incidence and mortality rates than the first period, the frequency of severe and extremely severe COVID-19 and the frequency and duration of hospitalizations decreased; however, the frequency of transfers into the intensive care unit and artificial lung ventilation slightly increased.