Epidemiological characteristics of varicella in Changping district of Beijing, 2012-2016

Abstract

Objective To understand the epidemiological characteristics of varicella epidemic in Changping district in recent years. Methods Varicella cases and their general information were collected from the case records (4 430) in Changping district during 2012-2016 in the China Information System for Diseases Control and Prevention and in the Information Management System for Immunization Program of Beijing. Population vaccination data against varicella were derived from the case investigation questionnaires on suspected chickenpox cases in all vaccination clinics of Changping district and the Information Management System for Immunization Programm of Beijing. Demographic data were obtained from the Statistics Bureau of Changping district. Descriptive epidemiological methods were used to analyze the incidence and distribution characteristics of these varicella cases. Results During 2012-2016, 4 430 varicella cases were reported in Changping district, with an average annual incidence of 49.20/100 000. During the study period, the highest incidence (92.29/100 000, 1 571 cases) was in 2012; the lowest incidence was in 2015 (32.64/100 000, 592 cases). The difference of incidences between years were statistically significantly (x2=940.62, P<0.01). For each year, more cases occurred in the spring and winter: from April to June (1 365 cases) and from October to next January (1 841 cases), accounting for 30.81% and 41.56% of all cases, respectively. As for age distribution, the 5-9 year group had the highest incidence (474.83/100 000, 1 177 cases), followed by the 10-14 year group (336.17/100 000, 586 cases); a trend that incidence decreased by age was evident (x2trend =15 105.11, P<0.01). The most impacted groups were kindergarten kids, primary school students and university students, which accounted for 66.16% (2 931/4 430) of total cases. In this study, 1 543 vaccine breakthrough cases were identified, which standed for 34.83% of all cases. Additionally, the incidence of population inoculated with 1 doses of vaccine was 1 732.94/100 000 (1 466 cases), and was much higher than that of those with two-dose of vaccine (120.74/100 000, 77 cases). The difference was statistically significant (x2=918.22, P<0.01). Conclusions In Changping district, nurseries and primary schools are the high-risk places for varicella. It is necessary to strengthen the epidemiological monitoring on varicella in kindergartens and schools. Study on varicella vaccine should be enhanced and the one-dose vaccinated group should be enrolled the emergency immunization program for reducing prevalence of varicella, especially the incidence of breakthrough cases. Key words: Chickenpox; Incidence; Demography; Cross-sectional studies