Brucellosis is a zoonotic disease caused by various Brucella species (1). Humans are infected most often though contact with sick animals, especially goats, sheep, and cattle, and through consumption of contaminated milk and milk products such as fresh cheese (1–2). In China, the main mode of transmission is contact with sick livestock such as sheep, goats, and cattle (3). Clinical features during the acute phase of human brucellosis are fever, hyperhidrosis, fatigue, and joint and muscle pain. If timely and effective treatment is not available during the acute phase, the infection can become chronic, which causes great suffering (4-5).
More than 170 countries and regions in the world have reported human and animal brucellosis (6). In the 1950s, brucellosis was widespread in China, with infection rates of human and animal brucellosis as high as 50% in severely affected areas. Following strengthened prevention and control measures based on the One Health approach, the brucellosis epidemic declined (7). However, at the beginning of the 21st century, human brucellosis had a resurgence in China, with sharply increasing incidences and widely expanded affected areas in the north and the south (8-9). In 2014 and 2015, the number of reported cases exceeded 50,000 per year, and the annual incidence rates were 4.22/100,000 and 4.18/100,000, which were historically high levels (8,10). To prevent and control human brucellosis, China’s Ministry of Agriculture and the National Commission of Health and Family Planning in 2016 co-issued a National Brucellosis Prevention and Control Plan (2016–2020) (11). The study analyzed the epidemiological characteristics of human brucellosis from 2016 to 2019 in China to evaluate progress of the national plan.
From 2016 to 2019, a total of 167,676 cases of human brucellosis was reported to NNDRS in the mainland of China, for an average annual incidence of 3.02/100,000 population. The annual number of cases reported nationwide was 47,139 (3.43/100,000) in 2016 and decreased to 38,554 (2.79/100,000) in 2017 and 37,947 (2.73/100,000) in 2018. Reported cases increased to 44,036 (3.15/100,000) in 2019. The peak season for human infections (by date of illness onset) was from March to August, accounting for 64.5% of cases in 2016–2019. The north and south had similar seasonal distributions (Figure 1).
Human brucellosis was reported in all 31 PLADs of the mainland of China; 95.2% (159,667) were reported from northern PLADs. Inner Mongolia reported the most cases (36,805 cases; 22.0% of all reports) and had an average annual incidence of 36.5/100,000. The other 10 PLADs with the highest number of cases were located in northern PLADs — Ningxia, Heilongjiang, Shanxi, Gansu, Liaoning, Jilin, Hebei, Henan, and Shandong (Figure 2), with average annual incidences ranging from 3.1/100,000 to 28.2/100,000. The incidence of human brucellosis was less than 1.0/100,000 in all southern PLADs; in Shanghai, the incidence was less than 0.1/100,000.
Figure 2. Human brucellosis in the ten provincial-level administrative divisions (PLADs) with the highest incidence rate of cases reported from 2016 to 2019.
High-burden PLADs differed in annual incidence patterns (Figure 2). Inner Mongolia had an upward trend with an annual incidence increasing from 23.8/100,000 in 2016 to 54.4/100,000 in 2019 — an average annual increase of 31.8%. Ningxia, Shanxi, Gansu, Shaanxi, Liaoning, and Hebei’s annual incidences declined and then increased. In Ningxia, brucellosis increased more than 8/100,000 from 2018 to 2019. In Heilongjiang, Jilin, and Henan, incidences declined in 2017 and remained relatively stable in 2018 and 2019. Xinjiang’s annual incidence decreased from 35.6/100,000 in 2016 to 16.3/100,000 in 2019 — an average annual decrease of 22.9% (Figure 2, Supplementary Table S1). Several provinces in southern China had significant annual increases in incidence, including Hainan (39.7%), Fujian (23.8%), Anhui (19.2%), and Hunan (7.5%) (Supplementary Table S1).
The percent of counties affected by brucellosis increased from 63.7% in 2016 to 65.9% in 2017 and decreased to 64.3% in 2019. Most affected counties were in northern PLADs. The percent of affected counties in southern PLADs increased from 40.4% in 2016 to 41.2% in 2019. The annual incidence of human brucellosis varied by county, with median incidences (interquartile range [IQR]) of 2.0 (0.5, 7.3)/100,000 in 2016 and 1.7 (0.5, 5.7)/100,000 in 2019. Counties in northern PLADs had higher median incidences than counties in southern PLADs: 4.4 (IQR: 1.6, 13.1)/100,000 vs. 0.4 (0.2, 0.7)/100,000 in 2016, and 3.4 (1.4, 10.9)/100,000 vs. 0.3 (0.2, 0.6)/100,000 in 2019. The 10 counties with the highest average annual incidence had incidences ranging from 124.5/100,000 to 265.0/100,000; among these, 6 were in Inner Mongolia, 3 in Xinjiang, and 1 in Ningxia. In 2019, the median of cases reported by county was 7 and was higher in northern China than in southern China (13 vs. 2) (Table 1, Supplementary Table S2).
Year Region Affected counties Incidence* (per 100,000) Number Percentage (%) 2016 South 591 40.4 (591/1,463) 0.3 North 1,286 86.8 (1,286/1,482) 7.8 Total 1,877 63.7 (1,877/2,945) 3.4 2017 South 657 44.9 (657/1,462) 0.3 North 1,286 86.6 (1,286/1,485) 6.3 Total 1,943 65.9 (1,943/2,947) 2.8 2018 South 597 40.9 (597/1,461) 0.2 North 1,298 87.3 (1,298/1,487) 6.2 Total 1,895 64.3 (1,895/2,948) 2.7 2019 South 603 41.2 (603/1,462) 0.2 North 1,294 87.0 (1,294/1,488) 7.2 Total 1,897 64.3 (1,897/2,950) 3.2 * Incidence was calculated as the total number of cases in each region divided by the total population in the same region.
Table 1. Comparison of human brucellosis between northern and southern China PLADs by numbers of affected counties and incidence (1/100,000), 2016–2019.
Farming and herding were the most common occupations of reported cases, accounting for 83.8% of reports. Houseworkers and unemployed individuals, students, and migrating individuals and kindergarten children accounted for 4.5%, 1.9%, and 1.1% of cases, respectively. The incidence among males was higher than that among females in all age groups and in the south and north, except for those aged 0–4 years and 5–9 (Figure 3 and Supplementary Table S3). People aged 45-64 years old had higher risk of infection than younger people. Those aged 45-64 years old had an incidence over 15.9/100,000 in the north in 2019, compared with over 7.0/100,000 among females (Figure 3 and Supplementary Table S3).