The changing epidemiology of bacillary dysentery and characteristics of antimicrobial resistance of Shigella isolated in China from 2004-2014

Abstract

Background: Bacillary dysentery caused by bacteria of the genus Shigella is a significant public health problem in developing countries such as China. The objective of this study was to analyze the epidemiological pattern of bacillary dysentery, the diversity of the causative agent, and the antimicrobial resistance patterns of Shigella spp. for the purpose of determining the most effective allocation of resources and prioritization of interventions.

Methods: Surveillance data were acquired from the National Infectious Disease Information Reporting System (2004-2014) and from the sentinel hospital-based surveillance system (2005-2014). We analyzed the spatial and temporal distribution of bacillary dysentery, age and sex distribution, species diversity, and antimicrobial resistance patterns of Shigella spp.

Results: The surveillance registry included over 3 million probable cases of bacillary dysentery during the period 2004-2014. The annual incidence rate of bacillary dysentery decreased from 38.03 cases per 100,000 person-years in 2004 to 11.24 cases per 100,000 person-years in 2014. The case-fatality rate decreased from 0.028% in 2004 to 0.003% in 2014. Children aged <1 year and 1-4 years were most affected, with higher incidence rates (228.59 cases per 100,000 person-years and 92.58 cases per 100,000 person-years respectively). The annual epidemic season occurred between June and September. A higher incidence rate of bacillary dysentery was found in the Northwest region, Beijing and Tianjin during the study period. Shigella flexneri was the most prevalent species that caused bacillary dysentery in China (63.86%), followed by Shigella sonnei (34.89%). Shigella isolates were highly resistant to nalidixic acid (89.13%), ampicillin (88.90%), tetracycline (88.43%), and sulfamethoxazole (82.92%). During the study period, isolates resistant to ciprofloxacin and cefotaxime increased from 8.53 and 7.87% in 2005 to 44.65 and 29.94% in 2014, respectively.

Conclusions: The incidence rate of bacillary dysentery has undergone an obvious decrease from 2004 to 2014. Priority interventions should be delivered to populations in northwest China and to individuals aged <5 years. Antimicrobial resistance of Shigella is a serious public health problem and it is important to consider the susceptibility profile of isolates before determining treatment.

Keywords: Bacillary dysentery; Epidemiology; Resistance; Shigella.

Fig. 1

Incidence rate and case-fatality rate of bacillary dysentery in China, 2004–2014

Fig. 2

Age and sex distribution of bacillary dysentery in China, 2004–2014. a The average annual incidence of bacillary dysentery by age and sex was calculated by dividing the total number of cases occurring in a specific age group during 2004–2014 by the corresponding population and multiplying by 100,000. b The proportion of bacillary dysentery cases by age groups

Fig. 3

Seasonal distribution of bacillary dysentery cases in China, 2004–2014. a The frequency distribution of bacillary dysentery cases by month of illness onset. b The seasonal index of bacillary dysentery. The seasonal index was calculated by month as the average case count for a given month divided by the average monthly case count during the entire 11-year time period, 2004–2014. No obvious seasonal pattern was expected if the seasonal index of each month was close to 1.0

Fig. 4

Spatial patterns of bacillary dysentery morbidity in China, 2004–2014. a Average incidence by province, 2004–2014. b–d Average incidence by province for three time periods (2004–2006 [b], 2007–2009 [c], and 2010–2014 [d]). Average incidence by province for different time periods was calculated by dividing the total number of cases in each time period by the corresponding population and multiplying by 100,000

Fig. 5

Proportion of Shigella spp. isolated in laboratory-confirmed cases of bacillary dysentery by year and province in sentinel hospitals, 2005–2014. a The temporal distribution of the proportion by Shigella spp. b The geographical distribution of the proportion by Shigella spp.

Fig. 6

Proportion of Shigella isolates resistant to different antimicrobial drugs in China, 2005–2014. a Proportion of Shigella isolates resistant to nalidixic acid, ampicillin, tetracycline, sulfamethoxazole, and amoxicillin. b Proportion of Shigella isolates resistant to Cephalothin, Gentamicin, Ciprofloxacin, and Cefotaxime. The proportion was calculated by dividing the number of isolates resistant to each antibiotic by all tested isolates