Characterization of an outbreak of hand, foot, and mouth disease in Nanchang, China in 2010

Abstract

Recent outbreaks of human enterovirus 71 (EV71) infection and EV71-associated hand, foot, and mouth disease (HFMD) in China have affected millions and potentially lead to life-threatening complications in newborns. Furthermore, these outbreaks represent a significant global public health issue in the world. Understanding the epidemiology of HFMD and EV71 infection and their transmission patterns in China is essential for controlling outbreaks. However, no studies on the outbreaks of HFMD and EV71 infection in China during 2010 have been reported. In this report, we carried out an epidemiological analysis to study an outbreak of HFMD and EV71 infection in 2010 in the city of Nanchang in the Jiangxi province of People's Republic of China. From April 7 to May 11, 2010, a total of 109 HFMD cases were reported, and in this report the HFMD cases were studied by both epidemiological and laboratory analyses. The epidemiological study indicates that children aged younger than 8 years old represented more than 90% of the reported cases, with the age group of 1-3 years containing the highest number of cases. Laboratory studies detected a high prevalence of EV71 amongst the cases in our study, suggesting EV71 as a common enterovirus found in HFMD cases in Nanchang. Phylogenetic analysis of the sequence of the VP1 region of four EV71 isolates indicated that the Nanchang strains belong to the C4 subgenotype commonly found in China during outbreaks in 2008 but contain distinct variations from these strains. Our study for the first time characterizes the epidemiology of HFMD and EV71 infection in China in 2010 and furthermore, provides the first direct evidence of the genotype of EV71 circulating in Nanchang, China. Our study should facilitate the development of public health measures for the control and prevention of HFMD and EV71 infection in at-risk individuals in China.

Figure 1

Geographic location of Nanchang in China (A) and of different HFMD cases (represented in red) in the metropolitan area (B) and city of Nanchang (C).

Figure 2. PCR reactions detecting the VP1 sequence of enterovirus 71 from samples isolated from different HFMD cases in Nanchang.

RT-PCR reactions were carried out in the absence of any RNA samples (negative control)(N, lane 2) or in the presence of a positive RNA sample (P, lane 3) or RNA samples isolated from HFMD cases NC10013 (lane 4), NC10014 (lane 5), NC10015 (lane 6), NC10016 (lane 7), NC10017 (lane 8), NC10018 (lane 9), NC10019 (lane 10), NC10020 (lane 11), and NC10021 (lane 12). The amplified products were separated in 1% agarose gels. M, DL2000 DNA marker ladder (TaKaRa) (lane 1).

Figure 3

Weekly distribution of the cases of HFMD (A) and those that were tested positive in our PCR assays for enterovirus (EVU), enterovirus 71 (EV71), and coxsackievirus 16 (CA16), and positive for both EV71 and CA16 (CA16/EV71), respectively (B).

Figure 4

Age distribution of the cases of HFMD (A) and those that were tested positive in our PCR assays for enterovirus (EVU), enterovirus 71 (EV71), and coxsackievirus 16 (CA16), and positive for both EV71 and CA16 (CA16/EV71), respectively (B).

Figure 5. Gender distribution of the cases of HFMD and those that were tested positive in our PCR assays for enterovirus (EVU), enterovirus 71 (EV71), and coxsackievirus 16 (CA16), and positive for both EV71 and CA16 (CA16/EV71), respectively.

Figure 6. Nucleotide sequence comparison of a part of the VP1 genes between four EV71 strains isolated in Nanchang and the reference viruses EV71-BrCr (BrCr) and EV71-FYC4 (FYC4).

The nucleotides that are not identical among all the virus sequences are highlighted. Numbering starts at the 5′ terminus of the EV71 genome.

Figure 7. Phylogenetic analysis of the four EV71 isolates from Nanchang and the reference viruses.

The evolutionary relationships among these viruses were estimated by the method of the neighbor-joining method with 1000 bootstraps. Sequence comparisons to the reference viruses were performed by a multiple alignment of the nucleotide sequences of the VP1 region.