Epidemiology of Genital Chlamydial Infection in China in 2019

Xiao-Li Yue, Xiang-Dong Gong,*, Jing Li, Jia-Hui Zhang, Heng Gu,*

1National Center for STD Control of the Chinese Center for Disease Control and Prevention, Nanjing, Jiangsu 210042, China;2Hospital for Skin Diseases (Institute of Dermatology), Chinese Academy of Medical Sciences and Peking Union Medical College,Nanjing, Jiangsu 210042, China.

Abstract Objective: Genital chlamydial infection is a globally common sexually transmitted infection caused by Chlamydia trachomatis.This study aimed to describe the epidemiological characteristics of the disease reported in China in 2019.

Keywords: genital chlamydial infection, incidence, trends, China

Introduction

According to the World Health Organization, about 127 million new cases of genital chlamydial infection,which is caused by Chlamydia trachomatis(C.trachomatis), occurred in 2016 worldwide.1Untreated genital chlamydial infection can result in epididymitis in men and pelvic inflammatory disease in women, which is a major cause of infertility, ectopic pregnancy, and chronic pelvic pain.2Asymptomatic genital chlamydial infection is more common in women than in men.Pregnant women infected with chlamydia can pass the infection to their infants during delivery, potentially resulting in ophthalmia neonatorum and pneumonia.3-4In China,genital chlamydial infection is not a notifiable disease.However,the reporting of nongonococcal urethritis caused by pathogens such as

C.trachomatis and Ureaplasma urealyticum began in China in 1991.5From 2008, genital chlamydial infection has been reported separately to nongonococcal urethritis in national sexually transmitted disease(STD)surveillance sites in China.The incidence of genital chlamydial infection in China increased from 2008 to 2015.6The present study describes the epidemiological characteristics of genital chlamydial infection in China in 2019 to enhance understanding of the recent epidemic.

Materials and methods

Data sources

Data on genital chlamydial infection cases treated at STD surveillance sites were collected through the National Notifiable Infectious Disease Reporting System developed by the Chinese Center for Disease Control and Prevention.The current rules and process of case reporting in China are:(a) universal case reporting is implemented within 105 district-based sites distributed in 31 provinces,autonomous regions, and municipalities; (b) when a new case of chlamydia is diagnosed in a medical facility in accordance with the National Diagnostic Criteria,7the doctor completes the National Form of Infectious Disease, and the case is inputted to the National Notifiable Infectious Disease Reporting System within 24hours by a specific healthcare worker; (c) to ensure the quality of the data,information on genital chlamydial infection cases are validated by the staff at the local center for disease control and prevention.The population data reported in the present study were obtained from the National Bureau of Statistics.

Statistical analysis

Descriptive analyses were performed using SPSS 18 software.Incidences were calculated as the number of genital chlamydial infection cases divided by the total population.The overall incidence was analyzed, as were the incidences per surveillance site, province, sex, and age group.The sex ratio and proportion of genital chlamydial infection cases by reporting source were also calculated.

Results

Overall incidence and trends of genital chlamydial infection

In 2019, a total of 50,874 cases of genital chlamydial infection were reported at 105 national STD surveillance sites.This case count corresponds to an incidence of 55.32 cases per 100,000 population, an increase of 9.98%compared with the incidence in 2018 (50.30 cases per 100,000) and an increase of 48.79% from 2015 (37.18 cases per 100,000).

Geographic distribution

The average incidences of genital chlamydial infection classified by the province in which the reporting sites were located are shown in Table 1.The incidence within each province ranged from 0.00 to 233.37 cases per 100,000 population.Zhejiang province had the highest incidence of reported cases, followed by Guangdong province(208.15 cases per 100,000 population), Guangxi autonomous region (144.33 cases per 100,000 population),and Hainan province (137.49 cases per 100,000 population);these four provinces(comprising 16 surveillance sites)accounted for 83.13% (42,290/50,874) of all cases of genital chlamydial infection.Thirteen provinces had incidences of genital chlamydial infection of lower than 10 cases per 100,000 population.No new cases of genital chlamydial infection were reported in Qinghai and Tibet in 2019(Table 1).

Sex and age distribution

In 2019,the numbers ofreportedcases of genital chlamydial infection in females and males were 38,027 and 12,847,respectively,giving incidences of 84.55 and 27.35 cases per 100,000 population,respectively.The incidence of genital chlamydial infection was much higher in females than in males, with a female-to-male ratio of 3.09:1; this was particularly evident in young people aged 15-29 years(female-to-male ratio 3.71-4.90:1).

The incidence of genital chlamydial infection was highest in those aged 20-24 years (184.70 cases per 100,000),followed by those aged 25-29 years (180.79 cases per 100,000) and 30-34 years (151.53 cases per 100,000).Stratification of the age-specific incidences of genital chlamydial infection by sex showed that the peak incidence occurred in the 30-34 year age group in males(79.05 cases per 100,000 population)and the 20-24 year age group in females(317.04 cases per 100,000 population)(Fig.1).

Distribution by reporting source

In 2019, 34,745 (68.30%) cases of genital chlamydial infection were reported by general hospitals, and 12,021(25.59%) were reported by maternal and child health hospitals.A total of 3,108 (6.16%) cases were reported from specialized dermatovenereology hospitals and other reporting sources (Fig.2).

Discussion

The present results showed that the incidence of genital chlamydial infection was 55.32 cases per 100,000 population in China in 2019, which is much higher than the incidence of gonorrhea(9.59 cases per 100,000 populaiton in 2018) in China8and suggests that genital chlamydial infection has been a common STD in China.However,the incidence of genital chlamydial infection in China was much lower than that reported in the United States, Canada,Australia,andEngland.9-12This maybe related to thelower rates of laboratory screening in China compared with othercountries, as a survey on genital chlamydial infection screening in STD surveillance sites showed that only 23.4%of medical institutions in China conducted nucleic acid amplification tests for chlamydia in 2017.Therefore, the incidence of genital chlamydial infection in China may be severely underestimated due to underdiagnosis and underreporting.

Table 1 Number of cases and incidence of genital chlamydial infection reported in 31 provinces and municipalities in China in 2019.

The incidence of genital chlamydial infection increased by 48.79% from 2015-2019 in China, similar to the trends reported in the United States, Canada, and Australia.9-11The marked increase in the incidence of genital chlamydial infection may be due to a real epidemic;however,it may also be related to increased screening and increased use of more sensitive tests such as nucleic acid amplification rather than rapid antigen tests.A survey conducted at 105 national STD surveillance sites in China showed that the proportion of nucleic acid amplification testing increased from 10.59% in 2008 to 23.4% in 2017.13The increased use of more sensitive diagnostic tests has likely increased the number of genital chlamydial infections being identified and reported, independent of actual increases in incidence.

The incidence of genital chlamydial infection varied greatly between provinces in China.A higher incidence was observed in STD surveillance sites located in southeast coastal areas in China (Zhejiang, Guangdong province,Guangxi autonomous region,and Hainan province)than in sites located in north and northwest regions (Jilin,Heilongjiang, Gansu, Qinghai, and Tibet).Furthermore,STD surveillance sites located in urban areas had higher incidences of genital chlamydial infection than sites located in rural areas.6This difference may be explained by differences between national STD surveillance sites in the socioeconomic status,availability of health services,laboratory screening, diagnosis, and reporting.The higher incidence of genital chlamydial infection in southeast coastal areas may be related to the developed economy,better management system for the disease,high level of detection,and availability of diagnostic facilities in this region.