Analysis of the prevalence and structure of asymptomatic SARS-CoV-2 carriage among adolescents and adults in Saint Petersburg during the COVID-19 epidemic rise in January 2022


DOI: https://dx.doi.org/10.18565/epidem.2022.12.1.11-7

Bashketova N.S., Fridman R.К., Kataeva I.S., Shapar A.O., Kostina M.A., Zhuravlev A.S., Lizinfeld I.A., Pshenichnaya N.Yu.

1) Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being Directorate for the City of Saint Petersburg, Saint Petersburg, Russia; 2) Center of Hygiene and Epidemiology in the City of Saint Petersburg, Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being, Saint Petersburg, Russia; 3) Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being, Moscow, Russia; 4) M.F. Vladimirsky Moscow Regional Research Clinical Institute, Moscow, Russia; 5) Central Research Institute of Epidemiology, Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being, Moscow, Russia
Objective. To analyze the prevalence and structure of asymptomatic SARS-CoV-2 carriage among the students and teachers of Saint Petersburg colleges during the rise in the incidence of COVID-19 in January 2022.
Subjects and methods. In January 25 to 27, 2022, nasopharyngeal and oropharyngeal samples were collected from 3,886 out of 8,350 students and teachers from 4 colleges located in different districts of Saint Petersburg. The examinees had no signs of acute respiratory viral infections and other symptoms that did not rule out COVID-19. The samples were examined by PCR assay for SARS-CoV-2 RNA. The positive samples were tested for mutations to the omicron and delta variants using the laboratory PCR procedure developed by the Pasteur Research Institute of Epidemiology and Microbiology, Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being. Laboratory studies were conducted in the Saint Petersburg Center for Hygiene and Epidemiology.
Results. There was a high detection rate of asymptomatic SARS-CoV-2 positive persons among the students and teachers of Saint Petersburg educational establishments during the rise in the incidence of COVID-19 caused by the predominant omicron variant. On average, in 14–17-year old adolescents, the frequency of both positive samples (20.6%) and the proportion of the omicron variant in the positive samples (51.7%) were significantly higher than in the persons aged 18 years and older (10.1 and 33.1%, respectively). This pattern was observed in all the analyzed educational establishments. The adolescents aged 14–17 years were statistically significantly 2.3 times more frequently asymptomatic virus carriers than the adults. In addition, among them, people who were 3.3 times more identified to be infected with the omicron variant than to the cohort of the studied individuals aged 18 years and older. There was a significant direct correlation between the increased number of the subjects to be tested and the probability of detecting asymptomatic carriers, including those infected with the omicron variant.
Conclusion. During the rise in the incidence of COVID-19 in January 2022, there was a high prevalence of asymptomatic SARS-CoV-2 carriage among the students and teachers of educational establishments located in different parts of the city. The findings suggest that it is inadvisable to examine and isolate contact persons from amongst the students and teachers of educational establishments, who have no clinical manifestations of the infection. The examination and isolation of people with symptoms of the disease, the transfer of risk-group people to online work or education, as well as enhanced monitoring of compliance with nonspecific prevention measures in all public institutions remain relevant.
Keywords: omicron, asymptomatic carriage, SARS-CoV-2, morbidity, prevalence
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About the Autors

Natalia S. Bashketova, Head, Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being Directorate for the City of Saint Petersburg, Russia; uprav@78rospotrebnadzor.ru
Roman K. Fridman, Cand. Med. Sci., Head Physician, Center of Hygiene and Epidemiology in the City of Saint Petersburg, Russia; centr@78cge.ru
Irina S. Kataeva, Deputy Head, Department of Epidemiological Surveillance; Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being Directorate for the City of Saint Petersburg, Russia; yvarova-irina@yandex.ru
Aleksandr O. Shapar, Head, Department of Epidemiology, Parasitology, and Disinfectology with a Group for the Recording and Registration of Infectious and Parasitic Diseases, Center of Hygiene and Epidemiology in the City of Saint Petersburg, Russia; ancentr@78cge.ru
Marina A. Kostina, Head, Department of Control and Surveillance Activities and Organization of Sanitary and Epidemiological Regulation, Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being, Moscow, Russia; depart@gsen.ru
Andrey S. Zhuravlev, Junior Researcher, Department of Radioendovascular Surgery, M.F. Vladimirsky Moscow Regional Research Clinical Institute, Moscow, Russia;: andrew0898@yandex.ru; Irina A. Lizinfeld, Consultant, Central Research Institute of Epidemiology, Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being, Moscow, Russia; irinalizinfeld@gmail.com; http://orcid.org/0000-0002-8114-1002
Professor Natalia Yu. Pshenichnaya, MD, Deputy Director for Clinical and Analytical Work, Central Research Institute of Epidemiology, Russian Federal Service for Supervision of Consumer Rights Protection and Human Well-Being, Moscow, Russia; pshenichnaya@cmd.su; http://orcid.org/0000-0003-2570-711X


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