The present study aimed to assess antibody seropositivity prevalence among symptomatic individuals and individuals with a high risk of occupational exposure to SARS-CoV-2. Participants from Chelyabinsk (Russian Federation) who were at an increased risk of exposure to SARS-CoV-2 (high-risk group, n = 1091) and participants who either had symptoms consistent with COVID-19 or were suspected to have experienced COVID-19 in the past (symptomatic group, n = 692) were enrolled between 28 September and 30 December 2020. Blood samples were tested by enzyme-linked immunosorbent assay D-5501 SARS-Cov-2-IgG-EIA-BEST and D-5502 SARS-Cov-2-IgM-EIA-BEST (AO Vector-Best, Novosibirsk, Russia). The overall seropositivity rate was 28.33–28.53%. SARS-CoV-2 antibodies were detected in 17.23% (adjusted prevalence of 17.17–17.29%) of participants in the high-risk and 45.95% (adjusted prevalence of 45.91–46.24%) in the symptomatic group. Higher IgG and IgM titers were observed in women compared to men, as well as in participants in the symptomatic group compared to those in the high-risk group. The results indicate that the seroprevalence among residents in several Russian regions is low (28.38%) and inadequate to provide herd immunity. The lower seroprevalence among participants in the high-risk group may be attributed to the enforcement of healthcare protocols and the use of adequate personal protective equipment.

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Epidemiological data on infections associated with medical care in surgical hospitals are presented. The features of the epidemic process of infections associated with Klebsiella spp. were studied among the patients of surgical profile. The study of the etiological structure in hemocultures in 33% of cases revealed the predominance of Klebsiella spp. In patients with a surgical profile, the incidence of Klebsiella spp. has increased over the past 10 years in wound content from 0,4 to 8,3% and in 7,7% of cases - in hemocultures. Significant resistance of Klebsiella spp. strains was detected currently used in the clinical practice of surgical hospitals antibacterial drugs. The highest sensitivity among Klebsiella spp. strains antimicrobial resistance was detected in the group of carbapenems. The structure of the epidemic process of infections caused by Klebsiella spp. is considered among patients of surgical clinics in 2018. In 32% of cases, the infectious process was localized in the lower respiratory tract, in 25% of cases - in the urinary tract, in 22% of cases - in the blood and in 21% of cases - in the area of surgical intervention. The results obtained do not differ significantly from the data obtained in other medical organizations in the country. The need for a comprehensive approach to microbiological monitoring and the appointment of antibacterial therapy for infections associated with the provision of medical care in surgical hospitals has been established. For example, the «Strategy for controlling antibacterial therapy» developed by the Russian Association of specialists in surgical infections, which is well-established in several dozen large hospitals in the country, is being more widely introduced into medical practice.

The current epidemiological characteristics of pathogens of especially dangerous infections abroad and in the Russian Federation are given. The biology of the causative agents of hemorrhagic fevers, as well as their species and subspecies, is especially reflected. The biology and epidemiology of the most common causative agents of hemorrhagic fevers are described in more detail: Dengue, Ebola, Marburg, Lassa, Machupo (Bolivian), Hanin (Argentinean) fever, Rift Valley fever, Omsk, Congo-Crimean, and renal fever their intermediate hosts - mosquitoes and ticks, the options for getting these pathogens into the human body. The most severe and widespread human infections, caused by alpha viruses and flaviviruses, the most severe epidemics in various countries are characterized. The modern systematics and immunopathogenesis of the causative agents of these infections, the features of virological and immunological diagnostics using both classical and modern techniques are presented. The new pathogens of hemorrhagic fevers, which have been fatal in recent years, are described. Given the current tense situation associated with the causative agents of hemorrhagic fevers, measures are proposed that are aimed at preventing the entry of pathogens into the Russian Federation, as well as the algorithm of actions of employees of medical institutions when patients with suspected infection associated with causative agents of especially dangerous infections are admitted.