Healthcare-workers are at risk of contact with measles cases and disease. Measles-infected employees of health facilities can contribute to the nosocomial spread of measles and can be a source of infection for the most susceptible of patients, such as pregnant women, newborns, and immunocompromised patients. In order to study the humoral immunity to measles among healthcare-workers and to reveal factors associated with seronegative status, we performed a cross-sectional study including 847 healthcare-workers of the Arkhangelsk Regional Clinical Hospital. We used “Vector-Best IgG-measles” enzyme linked immunosorbent assay test-systems (Russia) for quantitative measurement of anti-measles virus immunoglobulin G antibodies. According to the recommended by manufacturer cut-off values anti-measles immunoglobulin G titers of 0.18 IU/ml or higher were regarded as positive (protective), values between 0.12-0.17 – as equivocal, and a level of anti-measles virus antibodies 0.12 IU/ml or less was taken as negative. We use binary logistic regression analysis to assess predictors (gender, age, department, occupation) of seronegative status of health-care workers. Most of the study participants were female (92.1%). The median age was 48 (39; 57) years. The employees of somatic departments prevailed (26.7%). In 93.7% of medical workers, the concentration of anti-measles antibodies exceeded the protective titer (above 0.18 IU / ml), 4.4% were seronegative to measles, and 1.9% had equivocal results. The level of antibodies to measles was associated with age of healthcare-workers but it was not associated with gender. All employees older than 60 years were seropositive to measles. Among healthcare-workers younger than 35 years, only 77% had protective antibody titers. Staff aged 35 to 60 years were seropositive in 95.5% of cases. The proportion of participants with seronegative results did not depend on the position (doctor, nurse, cleaner) of healthcare-worker, but significantly varied between the departments. According to the results of logistic regression, the odds to have a seronegative test result among employees of somatic departments were 4.4 times higher in comparison with other departments. Among employees born between 1968 and 1984, the rate of seronegative results were 10 times less than among those, who were born after 1985. Among people older than 60 years, seronegative tests were obtained 50 times less often than among people younger than 35 years. The median concentration of measles immunoglobulin G among vaccinated healthcare-workers, 0.56 IU / ml, was significantly lower than among those, who had natural infection 4.2 IU / ml, p <0.001. Repeated test showed that in 5 years the titer of measles antibodies decreased in 1.2-1.9 times (average - 1.5). Thus, among medical stuff of a multidisciplinary health facility, the proportion people susceptible to measles was 6.3%. Age was the most important factor associated with seronegative status. Taking into consideration the decrease of antibody concentration in vaccinated healthcare-workers over time, seroprevalence studies and subsequent revaccination of seronegative people should be performed at least once in 5 years to prevent the spread of measles in healthcare facilities.
Genetic Analysis of the Measles Virus From the Outbreaks in South Korea, 2019
