Seroepidemiology of human Brucella infection in Yixing,China

Background

Brucellosis is one of the most common zoonotic diseases and remains an important public health problem in many countries. In China, human brucellosis is endemic and is continually reported from various parts of the country; it is usually found in people in occupational contact with the Brucella organism. ¹ Yixing was up till recently a non-endemic area for Brucella. The city has a population of 1.2 million, and is located in the centre of the Yangtze River Delta Urban Agglomeration. The first recorded laboratory-confirmed case of brucellosis in Yixing was a man who worked in a local abattoir and who probably had contact with infected goats at work in 2007. ² Since then, the local disease control council (CDC) has carried out effective hygiene education and surveillance. Ten cases were reported between 2007 and March 2015 in Yixing. All had occupational contact with goats. The data suggested that the risk existed among workers in local abattoirs. Determining the seroprevalence and the major risk factors among high-risk groups is thus very important to plan eradication of the disease. Our survey is thus useful in providing effective control and introducing preventative measures.

Methods

A total of 4198 blood samples were collected voluntarily from abattoir workers (n = 895) and the general rural population (n = 3303) in Yixing (age range, 16–85 years). All workers were from two local abattoirs where mainly goats were slaughtered. The pre-tested participants of the workers were all recruited by community health centre staff charged with directing local public-health work. Questionnaires including sociodemographic data (including name, gender, age, address, educational background, whether feeding poultry and livestock (especially goats), lifestyles, etc.) and occupational data (the time and duration of work, living habits: whether smoker, ingestion raw meat or half cooked meat, etc.), work habits, awareness rate of occupational prevention and knowledge about brucellosis, etc.) were collected with agreement from the participants.

All tests were done according to the diagnostic criteria for brucellosis (National Health and Family Planning Commission of China, WS 269-2007). All sera were primarily screened using the Rose-Bengal plate agglutination test (RBPT). By using the standard tube agglutination test (SAT) and a serial dilution method, a titre of 1:≥100 was considered positive.

Seroepidemiology in respect of population classification, gender and age was systematically analysed with SPSS version 17.0 for Windows. Chi-square and Fisher’s exact tests were used to compare categorical variables. A P value less than 0.05 was considered as statistically significant.

Results

Workers, who took part in this study were from two local large abattoirs in which over 300,000 goats are slaughtered each year. Eighty percent of the goats were not local, introduced from Anhui, Shandong, Inner Mongolia, Heilongjiang, Hebei and Jilin, among other sources. Out of 895 abattoirs workers, 147 (16.42%) showed the presence of antibodies against Brucella antigen by RBPT and SAT. No-one living in rural areas was found to be positive. Epidemiologic investigation proved that all seropositive subjects had a history of direct or indirect occupational contact with goats or their cadavers. A significant observation was the difference in seroprevalence between male and female workers where 18.93% (96/507) of the men and 13.14% (51/388) of the women were Brucella positive (P = 0.020) (Table 1). No significant difference of seropositivity was observed in age groups (P = 0.224) (Table 1). All workers had participated in one or more of the following tasks:. strangling and bleeding (17.1%, 58/341), fur, milk and mutton processing (15.97%, 46/288), skinning (15.28%, 22/144), animal consignment (15.69%, 8/51), washing equipment (21.74%, 5/23) and other jobs (16.67%, 8/48). No statistical difference was found according to type of work (P = 0.979). No workers had the habit of eating raw or half-cooked meat. There was no correlation between Brucella infection and education background, living or work habits, awareness rate of occupational prevention and knowledge about brucellosis.

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Table 1.

Gender and age group distribution of seroprevalence of brucellosis.

	n	Seroprevalence (n, %)	P value
Gender
Male	507	96 (18.93)	0.020
Female	388	51 (13.14)
Age (years)
≤25	78	15 (19.23)	0.224
26–35	53	6 (11.32)
36–45	202	29 (14.36)
46–55	225	31 (13.78)
≥56	337	66 (19.58)

Discussion

Brucellosis is one of the most prevalent zoonosis in the world. In China, 57,222 cases were reported in 2014 (National Health and family Planning Commission of China data, 2015-02-16 http://www.nhfpc.gov.cn/jkj/s3578/201502/847c041a3bac4c3e844f17309be0cabd.shtml), mostly occurring in six provinces: Inner Mongolia, Shanxi, Heilongjiang, Hebei, Jilin and Shannxi. Contact with infected animals has been reported as one of the important risk factors for brucellosis in some previous studies.^1,3–9 Yixing, an important industrial city in southern China, is located far from the Brucella-endemic areas of northern China. Our study has, however, demonstrated a high seroprevalence of Brucella among local abattoir workers in Yixing. Brucella infection probably occurs through cuts and wounds on bare hands or through splashing of infected blood or other fluid to the conjunctiva. This implies that infection was mainly due to lack of occupational protection, and that the origin of Brucella infection can be traced to infected goats and their products introduced from other provinces in China. The higher rate of seroprevalence of brucellosis in men compared to women was probably due to an increased involvement of men in handling animals and their products.

Indeed, lack of basic occupational protection at work, such as latex gloves, was found in 90.0% of the working population in Yixing.^2,11 In the absence of a human brucellosis vaccine, prevention of human brucellosis depends on the control of the disease in animals.

In recent years, human brucellosis cases have spread quickly from rural to urban areas, ¹⁰ indicating the failure of quarantine for infected animals. Although no cases were identified in people living in rural areas in our study, that does not mean they would not suffer the threat of Brucellosis. Quarantine of animals is necessary before introduction and replacement, however it is difficult to perform because of the lack of supportive actions from various sectors, which puts ordinarily low-risk people at a much higher risk when they consume or handle infected animal meat and milk. Our results should be useful for providing instructions and recommendations for the government on epidemic risk responses to brucellosis. We urgently need to carry out the environmental and occupational hygiene education in the community and in the household as well as on the sequence of actions detect and treat patients to protect the human healthy from brucellosis.