An atypical winter outbreak of hand, foot, and mouth disease associated with human enterovirus 71, 2010

Abstract

Background: To analyze the epidemiological characteristics and pathogenic molecular characteristics of an hand, foot, and mouth disease (HFMD) outbreak caused by enterovirus 71 in Linyi City, Shandong Province, China during November 30 to December 28, 2010.

Methods: One hundred and seventy three stool specimens and 40 throat samples were collected from 173 hospitalized cases. Epidemiologic and clinical investigations, laboratory testing, and genetic analyses were performed to identify the causal pathogen of the outbreak.

Results: Among the 173 cases reported in December 2010, the male-female ratio was 1.88: 1; 23 cases (13.3%) were severe. The majority of patients were children aged < 5 years (95.4%). Some patients developed respiratory symptoms including runny nose (38.2%), cough (20.2%), and sore throat (14.5%). One hundred and thirty eight EV71 positive cases were identified based on real time reverse-transcription PCR detection and 107 isolates were sequenced with the VP1 region. Phylogenetic analysis of full-length VP1 sequences of 107 Linyi EV71 isolates showed that they belonged to the C4a cluster of the C4 subgenotype and were divided into 3 lineages (Lineage I, II and III). The two amino acid substitutions (Gly and Gln for Glu) at position 145 within the VP1 region are more likely to appear in EV71 isolates from severe cases (52.2%) than those recovered from mild cases (8.3%).

Conclusion: This outbreak of HMFD was caused by EV71 in an atypical winter. EV71 strains associated with this outbreak represented three separate chains of transmission. Substitution at amino acid position 145 of the VP1 region of EV71 might be an important virulence marker for severe cases. These findings suggest that continued surveillance for EV71 variants has the potential to greatly impact HFMD prevention and control.

Figure 1

Epidemic curve of the HMFD outbreak in Linyi City, Shandong Province, China, 2010.

Figure 2

Dendrogram showing the phylogenetic relationships of 107 EV71 isolates in this outbreak and other genotypes of EV71 isolates from GenBank based on VP1 sequence alignment, which was constructed using Mega software (version 5.2).

Figure 3

Phylogenetic tree of 107 EV71 isolates in this outbreak and related C4a subgenotype strains. Accession numbers are given in parentheses. ▲, isolates from severe cases. LY, isolates from this study; SD, Shandong Province; ZJ, Zhejiang Province; BJ, Beijing City; JS, Jiangsu Province; CQ, Chongqing City.

Figure 4

Amino acid sequence alignment of the full length VP1 region of the EV71 virus isolates in Linyi City, Shandong Province, 2010. Amino acid sequences were numbered according to the sequence of EV71_BrCr (Genbank accession number: ETU22521). Identical residues are indicated as dots. Amino acids that differ from the consensus sequence are shaded. ▲, isolates of severe cases.