ABSTRACT
Introduction. SARS-CoV-2 can be transmitted by infected people without or with mild symptoms of acute respiratory infection (ARI). Monitoring based on nucleic acid amplification techniques is used to measure the prevalence of ARI pathogens and to assess the effectiveness of preventive measures. The aim is to measure the prevalence of pathogens causing ARIs of viral etiology, influenza, and COVID-19 among individuals without ARI symptoms throughout age groups, to trace changes in the epidemic situation by weekly monitoring pathogens during the inter-epidemic period and at the beginning of a typical ARI epidemic season, to assess the effectiveness of medical masks for prevention of the above infections. Materials and methods. A total of 14,119 people (including 4,582 children) without ARI symptoms went through examination, including questionnaire surveys, in 26 regions of Russia from August to October 2020. Nasopharyngeal and oropharyngeal swabs were tested by using AmpliSens ARVI-screen-FL, AmpliSens Influenza virus A/B-FL, and AmpliSens Cov-Bat-FL reagent kits (The Central Research Institute of Epidemiology of Rospotrebnadzor, Moscow). Results. 11.1% of the tested samples showed positive results;the rhinovirus prevailed (7.32%), while SARS-CoV-2 was detected in 1.66%. In autumn, the proportion of SARS-CoV-2 infected cases increased from 0.49% to 4.02% (p < 0.001). The SARS-CoV-2 RNA concentration was up to 1010 copies/mL. Conclusions. Differences in the prevalence of SARS-CoV-2 and rhinovirus among the age groups and over time were found and analyzed. Using of medical masks reduced the risk of infection with respiratory viruses and with SARS-CoV-2 by 51% and 34%, respectively. In case of prolonged exposure to a COVID-19 patient, healthy people must use a respirator for more effective protection. The individuals whose work was associated with a high level of social contacts were infected more rarely than other individuals in the same age group (p = 0.001);this fact supports the importance of anti-epidemic measures and commitment to their adherence by people whose profession entails frequent social contacts. © 2021, Central Research Institute for Epidemiology. All rights reserved.
ABSTRACT
The first case of COVID-19 was diagnosed in St. Petersburg on March 2, 2020;the period of increase in the incidence lasted for 10 weeks, the maximum rates were recorded in mid-May, and subsequently there was a statistically significant decrease in the incidence. Objective: to determine the level and structure of community immunity to SARS-CoV-2 among the population of St. Petersburg during the period of intensive spread of COVID-19. Materials and methods. Selection of volunteers for the study was carried out through interviewing and randomization. The exclusion criterion was active COVID-19 infection at the time of the survey. 2713 people aged 1 to 70 years and above were examined for the presence of specific antibodies to SARS-CoV-2. Antibodies were detected by enzyme immunoassay. Results and discussion. Studies have shown that in St. Petersburg, in the active phase of COVID-19 epidemic, there was a moderate seroprevalence to SARS-CoV-2, which amounted to 26 %, against the background of a high frequency (84.5 %) of asymptomatic infection in seropositive individuals who did not have a history of COVID-19 disease, positive PCR result and ARI symptoms on the day of examination. The maximum indicators of herd immunity were established in children 1–6 years old (31.1 %), 7–13 years old (37.7 %) and people over 70 years old (30.4 %). Differences in the level of seroprevalence in the age groups of 18–49 years are statistically significant. The highest level of seroprevalence was found among the unemployed (29.7 %), healthcare workers (27.1 %), education sector (26.4 %) and business sector personnel (25 %). In convalescents, COVID-19 antibodies are produced in 75 % of cases. In individuals with positive result of PCR analysis carried out earlier, antibodies are detected in 70 % of the cases. The results of the study of herd immunity to SARS-CoV-2 are essential to forecast the development of the epidemiological situation, as well as to plan measures for specific and non-specific prevention of COVID-19. © 2020 Russian Research Anti-Plague Institute. All rights reserved.