A Systematic Review and Meta-Analysis of Epidemiology and Clinical Manifestations of Human Brucellosis in China

Background. Brucellosis has a wide spectrum of clinical manifestations and it may last several days or even several years; however, it is often misdiagnosed and therefore may cause inadequate therapy and prolonged illness. Previous studies about meta-analysis of manifestations of brucellosis reported in English lacked the data published in Chinese, which did not provide details about the contact history, laboratory tests, and misdiagnosis. We undertake a meta-analysis of clinical manifestations of human brucellosis in China to identify those gaps in the literature. We have searched published articles in electronic databases up to December 2016 identified as relating to clinical features of human brucellosis in China. 68 studies were included in the analysis. The main clinical manifestations were fever, fatigue, arthralgia, and muscle pain (87%, 63%, 62%, and 56%, resp.). There are significant differences between adults and children. Rash, respiratory and cardiac complications, and orchitis/epididymitis were more prevalent in children patients. The common complications of brucellosis were hepatitis, followed by osteoarthritis, respiratory diseases, cardiovascular diseases, central nervous system dysfunction, hemophagocytic syndrome, and orchitis/epididymitis in male. In the nonpastoral areas, brucellosis has a high ratio of misdiagnosis. Our analysis provides further evidence for the accurate diagnosis, particularly in assessing severe, debilitating sequelae of this infection.


Introduction
Brucellosis is one of the most common zoonotic infections globally [1,2]. The disease is transmitted to humans by direct/indirect contact with infected animals or through the consumption of raw meat and dairy products [3,4]. The main transmission routes are digestive tract, skin, and mucosal and respiratory tract contact with blood body fluids and aerosols.
Brucellosis has a wide spectrum of clinical manifestations, often lacks specificity, may last from several days to more than a year, is often misdiagnosed, and therefore causes inadequate therapy and prolonged illness can cause a severely debilitating and disabling illness. Patients may show fever, sweating, fatigue, and osteoarthritis [5] and even more serious conditions in different organ systems [6]. Brucellosis not only causes huge economic loss to the society by influencing the production of animal husbandry, but also threatens the human's physical and mental health [7].
Brucellosis was first reported in China in 1905 [8]. In recent years, human brucellosis incidence has increased sharply [9,10]. Nationwide surveillance data indicated that the total incidence rate of human brucellosis in mainland China increased from 0.92 cases/100,000 people in 2004 to 4.2 cases/100,000 people in 2014 [11][12][13]. Currently, human brucellosis remains one of major public health issues in China.
This study presents a systematic review of scientific literature published before December 2016 identified as relating to clinical features of brucellosis in China. The objectives of this review were to identify those gaps in the literature of epidemiology, clinical manifestations, contact history, laboratory tests, and misdiagnosis of human brucellosis in 2.2. Selection Criteria. We systematically and inclusively reviewed articles by two investigators. The reviewers selected articles first by title and abstract, next by full text, and last by analyzing eligible studies in detail until demonstrating 100% agreement in articles included and excluded by two investigators.
Studies with the following criteria were excluded: (A) articles related to non-human brucellosis; (B) reported data that overlapped with already included articles; (C) articles that could not provide original data of the patients; (D) articles addressing topics that were not related to the clinical features of human brucellosis, such as treatment intervention and experimental laboratory studies.
Studies with the following criteria were included: (A) the literatures that described the clinical symptoms/syndromes of human brucellosis and the number of study subjects must more than 10 in each document; (B) the subjects reported in the literature who must be in China; (C) studies that provided data from general brucellosis cases and presented relevant laboratory results.

Data Extraction.
Data was extracted by two reviewers independently including data collection, study design, study location, patient characteristics, the number of male and female patients, clinical manifestations, numbers of subjects with each symptom and complication which were recorded for each study, methods of diagnosis, and laboratory parameters. For the sex-related outcomes of epididymo/orchitis, the study population was considered to be only the male subgroups of the study population. Children patients must be of the age of 0-15 years. We also recorded the information relating to duration of illness prior to treatment, diagnostic delay, and exposure to potential risk factors. The results of data extraction must reach an agreement and consensus between the reviewers.

Statistical Analyses.
We defined an event rate as the ratio of number of reported cases with a specific clinical manifestation to the total number of reported cases in each study. R statistical software (version 3.4.2, meta package) will be used for creating Forest plots to summarize composite data, generating proportions and corresponding 95% confidence intervals for each manifestation. Two-sided values < 0.05 will be considered statistically significant during hypothesis testing.

Systematic Review.
Literature searches yielded 1991 potential articles, leaving 68 publications that met inclusion and exclusion criteria for data extraction and final analyses. 68 studies represented 12842 patients with human brucellosis in China. The male : female ratio was 2.64 : 1. All 68 articles included in the analysis were case series studies. Figure 1 illustrates the detailed search process. Studies selected from 20 provinces or autonomous regions of China, including 39 studies from pastoral areas (12 from Xinjiang, 9 from Heilongjiang, 7 from Inner Mongolia, 4 from Jilin, 4 from Ningxia, 2 from Gansu, and 1 from Liaoning) and 29 studies from nonpastoral areas (6 from Shandong, 5 from Beijing, 3 from Henan, 3 from Shanxi, 2 from Hebei, 2 from Shaanxi, 2 from Tianjin, 1 from Guangdong, 1 from Hunan, 1 from Jiangsu, 1 from Jiangxi, 1 from Yunnan, and 1 from Zhejiang). The geographic distributions of the numbers of subjects from each selected study are shown in Figure 2.

Discussion
Brucellosis is one of the most widespread zoonoses worldwide [82,83]. The number of brucellosis patients is increasing year by year in China. Shi et al. [84] analyzed the incidence and spatial-temporal distribution of human brucellosis from 1955 to 2014 in China, and the report showed that human brucellosis had reemerged since the mid-1990s and the affected areas had expanded from northern pastureland provinces to southern coastal and southwestern areas since 2004. In China brucellosis has been increasingly causing huge economic loss, and it has been a population health problem in recent years. In humans, brucellosis involved multiorgans with a complicated and various clinical presentations ranging from nonspecific to severe symptoms [85], which makes brucellosis easily misdiagnosed as other diseases. If a chronic phase is developed for a lack of timely diagnosis and treatment, the disease can lead to a high rate of disability. Since the clinical summary of the relevant cases in China is published in Chinese, these cases are not included in the study using metaanalysis of Brucella abroad [86]. We analyzed the literature of clinical manifestations of human brucellosis in China.
From our analyzed data, it shows that 57% selected studies from pastoral areas and 43% from nonpastoral and coastal areas, consistent with previous epidemiological findings that the disease affected areas have expanded from northern pastureland provinces to southern coastal and southwestern areas over the past decades in China, but brucellosis is still mainly popular in pastoral areas [87]. In this study, there are 79.4% of patients who had close contact with sick animals and 11.5% of cases had consumption of uncooked meat or dairy products, indicating that contacting with infected animals and consuming unsterile animal products are the main transmission routes in China.
In the study, we found that the main clinical manifestations of human brucellosis are fever, fatigue, arthralgia, and muscle pain. The most common clinical syndromes of adult patients are fever, muscle pain, arthralgia, and sweating. Similar to our study, in a systematic review of the clinical manifestations of human brucellosis [86], the authors found that fever, arthralgia, myalgia, and back pain affected around half of the patients (78%, 65%, 47%, and 45%, resp.). There is controversy about whether clinical manifestations in children are significantly different from manifestations in adults. It had been reported in the literature that there was no significant difference in clinical manifestations between children and adults [88], which was very different in different literature. Some scholars reported that enlarged lymph nodes, spleen and liver, skin rashes, pharyngitis [89], and hematological and respiratory complications were more frequently observed in children than in adults [90]. Children had higher rates of hepatitis, osteoarticular manifestations [91], and lower rates of meningitis, endocarditis, spondylitis, and the progression to chronicity [92]. In the study, we found clinical differences between children and adults. Children had higher rates of rash, respiratory and cardiac complications, and orchitis/epididymitis. We also noted that chills, headache, and weight loss are less frequently observed in children patients.
Multiorgan involvement of Brucella is probably underrecognised [93]. Bone, CNS, and epididymis are the most commonly included organs [6]. The results of the current study were similar to those in other reported articles [94]. In the current study, results show that hepatitis and osteoarthritis were the more frequent complications. Serious complications such as central nervous system dysfunction, cardiovascular diseases, respiratory manifestations, and hemophagocytic syndromes are also observed. Orchitis or epididymitis occurred in 9% of the male patients. Brucellosis complications remain a major medical problem and it must still be regarded as a serious health problem in China.
In the study, results show that there is a high rate of misdiagnosis that mainly occurred in nonpastoral areas. Because of these manifestations such as fever, back pain,   cough, gastrointestinal symptoms, and blood abnormalities, brucellosis is often misdiagnosed. Most misdiagnosed patients were admitted in Department of Rheumatology, Hematology, Orthopedics, and Respiration at the first visit. Brucella bacteria culture is the "gold standard" for the diagnosis of brucellosis [95,96]. In the study, 87% of brucellosis patients have fever. However, we found that only 30 articles including 4681 cases were tested by blood culture and 48.3% of cases were positive of Brucella melitensis, indicating it may be the main reason of inappropriate diagnosis and inadequate therapy. Therefore, in order to reduce the rate of misdiagnosis effectively especially in the nonpastoral areas and provinces with high incidence of tuberculosis, it is necessary to broaden the ideas of clinical diagnosis with detailed history and carried out agglutination test and blood culture as early as possible for fever patients. One challenge in diagnosis of brucellosis is that the most common laboratory abnormalities are nonspecific. Most patients have normal blood cell counts on presentation. In the study, we found that the common abnormal laboratory tests were aleucocytosis (24.1%), anemia (23.9%), thrombocytopenia (15.8%), pancytopenia (13.2%), and leukocytosis (10.6%). In case of pancytopenia, the diagnosis of secondary hemophagocytosis should be considered. This condition may be triggered by Brucella and other intracellular pathogens [97,98].
Our study has some limitations. First, although the incidence of brucellosis is very high in our country, the quantity and quality of articles reported in some provinces are not high, which leads to partial data omission. We failed to obtain more precise analysis of different clinical stages of brucellosis because part of the included literature did not clearly describe the brucellosis clinical stage and age classification. Second, most of the reported literatures lack detailed data on patient treatment options and prognosis, which results in the failure of analyzing therapeutic effect and prognosis.
In summary, we found that brucellosis was mainly popular in pastoral areas, but the disease affected areas had expanded from northern pastureland provinces to southern coastal and southwestern areas in China. The infection is mostly associated with the contact with infected animals or through the consumption of raw animal products. Clinical symptoms include fever, fatigue, arthralgia, sweating, and muscle pain with complication such as osteoarthritis, hepatitis, central nervous system dysfunction, cardiovascular diseases, respiratory manifestations, orchitis or epididymitis, and hemophagocytic syndromes. Further research is needed to characterize the analysis for therapeutic effect and prognosis of brucellosis in China. Our study provides initial evidence for the accurate diagnosis.

Conflicts of Interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.