Changing Epidemiology of Human Brucellosis, China, 1955-2014

Abstract

Brucellosis, a zoonotic disease, was made statutorily notifiable in China in 1955. We analyzed the incidence and spatial-temporal distribution of human brucellosis during 1955-2014 in China using notifiable surveillance data: aggregated data for 1955-2003 and individual case data for 2004-2014. A total of 513,034 brucellosis cases were recorded, of which 99.3% were reported in northern China during 1955-2014, and 69.1% (258, 462/374, 141) occurred during February-July in 1990-2014. Incidence remained high during 1955-1978 (interquartile range 0.42-1.0 cases/100,000 residents), then decreased dramatically in 1979-1994. However, brucellosis has reemerged since 1995 (interquartile range 0.11-0.23 in 1995-2003 and 1.48-2.89 in 2004-2014); the historical high occurred in 2014, and the affected area expanded from northern pastureland provinces to the adjacent grassland and agricultural areas, then to southern coastal and southwestern areas. Control strategies in China should be adjusted to account for these changes by adopting a One Health approach.

Keywords: Brucella; Brucellosis; China; bacteria; epidemiology; humans; zoonoses.

Figure 1

Reported human brucellosis cases (N = 513,034), mainland China, 1955–2014. A) Aggregated number of cases (blue bars) and annual incidence rate (orange line) per 100,000 residents reported by year. The adjusted incidence rate (green dashed line) was estimated by an excess proportion (22.06%) that might be attributed to the effect of Internet-based reporting since 2004 (see Methods). B) Forecast of the monthly number of cases (blue line) during 2015–2019 by Holt-Winters exponential smoothing with 80% CIs (light gray) and 95% CIs (dark gray) based on monthly numbers for 2004–2014.

Figure 2

Age distribution and proportion of 346,682 human brucellosis patients, mainland China, 2004–2014. A) Age distribution by sex. B) Annual proportion of patients by sex. C) Age distribution of persons with probable and confirmed cases. D) Annual proportion of probable and confirmed cases. E) Age distribution of patients in northern and southern China. F) Proportion of cases in northern and southern China each year.

Figure 3

Heat map of provinces with human brucellosis cases, by north and south and the latitude of the capital city of each province, China. A) Time series of incidence rate per 100,000 residents during 1955–2014, standardized by the eighth root. B) Time series of monthly cases, 2005–2014, standardized by the annual number of cases reported by each province. C) Seasonal distribution of cases by province, plotted as the mean value of the proportion of cases in each week of the year from 2005 through 2014.

Figure 4

Geographic distribution of the annual incidence rate per 100,000 residents of human brucellosis by 5-year periods, mainland China, 1990–2014.

Figure 5

Number of counties with human brucellosis cases, mainland China, 2004–2014. A) Total number of affected counties each year and number of newly affected counties since 2004. B) Total number of affected counties each year in northern and southern China.

Figure 6

Geographic expansion of human brucellosis across counties and distribution of land covers (28) and density of sheep and goats (29), mainland China, 2004–2014.