ABSTRACT
AIM: The mumps outbreak in the Plzen Region in 2011 was analysed retrospectively using the epidemiological, clinical, and laboratory data. Vaccine efficacy analysis was also conducted in various population groups. MATERIAL AND METHODS: The routine procedure and standard form were used by the epidemiologists to collect data on the age, sex, place of residence, presence in collectivities, date of disease onset, type of complications and date of their onset, hospital admission, vaccination, and results of laboratory analyses. Based on the records of general practitioners for children and adolescents, data on the vaccination of children born in the previous three years have been provided to the epidemic control departments every year by 30 June since 1989. To estimate the vaccination coverage rate, the numbers of single-dose or two-dose recipients are related to the number of children registered in a given year. The first year of vaccine recipients were children born in 1986 who were aged 25 in 2011. The data collected on the population of the Plzen Region were used for the primary analyses. To estimate the efficacy of the mumps vaccine, age and vaccine coverage cohort analysis was performed using the screening method. To analyse categories, the chi-square test with Yates correction was applied at a significance level of p = 0.05 % (EPIINFO version 6.04d). RESULTS: In 2011, 721 mumps cases were reported in the Plzen Region (incidence: 126.1 cases per 100 000 population). The average patient age was 19.4 years, with a median of 18 years (age range 1-77 years). Four hundred and seventeen (57.8%) patients were males. Biological specimens from 375 (52.0%) patients were investigated serologically in the virology laboratory and mumps were laboratory confirmed in 316 (43.8%) of them - in 222 patients, one blood specimen was analysed. The most afflicted area was the Klatovy district with the incidence of 449.3/100 000 population. The most affected age group were 15-19 year-olds with the incidence of 1008.2/100 000 population. Forty-two (5.8%) patients were diagnosed with complications and 68 (9.4%) patients were admitted to the hospital. No statistically significant difference was found in the incidence of complications between the vaccinated and non-vaccinated patients. The assessment of hospitalisation risk showed a statistically significant difference between the vaccinated and non-vaccinated persons in both the whole study cohort and subcohort of patients who received the mumps vaccine within the childhood immunization schedule (p = 0.000 and p = 0.004, respectively). The average age of the vaccinated patients was 16.1 years (median of 17) and that of the non-vaccinated patients was, 29.3 years (median of 27). At the six to ten-month interval, as laid down by the legislation, the second dose of the vaccine was only given to 83.6 % of the patients. The screening method showed a high efficacy of the vaccine in the age group 20-25 years (97.6% in two-dose recipients), declining to 29.6% in the most affected age group of 15-19 years. CONCLUSIONS: Mumps outbreak may has been a result of the accumulation of high numbers of susceptible individuals in the population. The most affected area was the Klatovy district where the last epidemic outbreak occurred 23 years ago. To make the favourable epidemiological situation with occasional local outbreaks continue, the high two-dose vaccine coverage rate needs to be maintained.
