Monitoring of SARS-COV-2 Antibodies in Tuberculosis In-Patient Clinic Stuff

Objective. Тo study the features of humoral immunity to SARS-CoV-2 among the medical stuff of an antitubercular hospital in the context of the spread of a new coronavirus infection. Materials and methods. The interim results of a single-center prospective observational study involving 350 employees of a pulmonary tuberculosis hospital that was not repurposed to work with COVID-19 are presented. The results of weekly monitoring of IgM and IgG levels for the period from May 15 to November 28, 2020, were analyzed in comparison with the results of diagnosis of COVID-19 cases (identification of the pathogen in a smear from the oropharynx and nasopharynx, changes in lung tissue according to computed tomography). Results. During the observation period, COVID-19 was detected in 106 people (30.3%). Antibodies to SARS-CoV-2 (IgG and/or IgM) were detected at the start of monitoring in 30 people (8.6%, 95%CI 5.8-12.2%), by the end of the follow – up period-in 95 people (27.1%, 95%CI 22.7- 32.0%). The frequency of detection of antibodies in the patients was 70.8% (95%CI 55.6-88.7%): IgM class in 23 (21.7%), G class in 73 (68.9%). The median time from disease detection to IgM detection was 1.5 weeks. (interquartile range 0-4 weeks), before the discovery of IgG – 4 weeks. (interquartile range 2-5 weeks). At any follow-up period, the chances of IgG production in the protective titer were higher in the case of moderate or severe disease with the development of pneumonia compared to the mild course (OR 2.6, 95%CI 1.1-6.3); the IgG titer was also higher (p < 0.01). «Atypical» variants of the antibody response were identified in individuals with confirmed COVID-19: no antibody formation (31 people), production of class M antibodies only (4 people); long-term persistence of IgG in a titer of less than 30 g/l, long ahead of the disease manifestation (6 people). The sensitivity of serological testing as a method for detecting current and / or transmitted coronavirus infection was 70.8% (95%CI 61.1-79.2%), and the specificity was 91.8% (95%CI 87.6-94.9%). Conclusion. The frequency of detection of antibodies to SARS-CoV-2 among employees of the TB hospital corresponds to the dynamics of the incidence of COVID-19. Virus-specific antibodies were detected in 70.8% of COVID-19 survivors (IgG in 68.9%); in the absolute majority of patients, the antibodies remained in a significant titer (IgG > 10 g/l) for 6 months or more at the start of testing. When the disease occurs without the development of viral pneumonia, the chances of forming a significant and persistent antibody response are significantly lower. Serological testing is a sensitive and highly specific method for detecting a previous COVID-19 disease.