Epidemiologic and virologic investigation of hand, foot, and mouth disease, southern Vietnam, 2005

Abstract

During 2005, 764 children were brought to a large children's hospital in Ho Chi Minh City, Vietnam, with a diagnosis of hand, foot, and mouth disease. All enrolled children had specimens (vesicle fluid, stool, throat swab) collected for enterovirus isolation by cell culture. An enterovirus was isolated from 411 (53.8%) of the specimens: 173 (42.1%) isolates were identified as human enterovirus 71 (HEV71) and 214 (52.1%) as coxsackievirus A16. Of the identified HEV71 infections, 51 (29.5%) were complicated by acute neurologic disease and 3 (1.7%) were fatal. HEV71 was isolated throughout the year, with a period of higher prevalence in October-November. Phylogenetic analysis of 23 HEV71 isolates showed that during the first half of 2005, viruses belonging to 3 subgenogroups, C1, C4, and a previously undescribed subgenogroup, C5, cocirculated in southern Vietnam. In the second half of the year, viruses belonging to subgenogroup C5 predominated during a period of higher HEV71 activity.

Figure 1

Flowchart showing the procedures used for isolating and identifying enterovirus strains cultured from clinical specimens obtained from children admitted to a large pediatric hospital in Ho Chi Minh City, Vietnam, with a diagnosis of hand, foot, and mouth disease (HFMD) during 2005 and enrolled in this study. EV, enterovirus; RT-PCR, reverse transcription–PCR; 5′ UTR, 5′ untranslated region; HEV71, human enterovirus 71.

Figure 2

Clinical features of hand, foot, and mouth disease (HFMD) in children admitted to hospital in southern Vietnam during 2005. Features were associated with the isolation of coxsackievirus A16 (CVA16) (214 cases) or human enterovirus 71 (HEV71) (173 cases) from vesicle, throat swab, or stool specimens. A) Percentage distribution of clinical signs and symptoms among identified cases of HFMD. B) Percentage age distribution of patients with identified cases of HFMD.

Figure 3

Monthly distribution of 387 cases of hand, foot, and mouth disease (HFMD) associated with isolation of either coxsackievirus A16 (CVA16) (214 cases) or human enterovirus 71 (HEV71) (173 cases), southern Vietnam, 2005. RNA was extracted from cells inoculated with vesicle, throat swab, or stool specimens. Partial VP4 gene sequences were amplified by reverse transcription–PCR (RT-PCR) by using specific primers (22), the amplified cDNA sequenced, and the serotype and/or genogroup specificity determined by BLAST analysis. A) Monthly distribution of CVA16 and HEV71-associated HFMD cases. B) Monthly distribution of 173 HFMD cases associated with HEV71 infection with strains belonging to subgenogroups C1, C4, or C5.

Figure 4

Geographic distribution of hand, foot, and mouth disease cases associated with human enterovirus 71 (A) or coxsackievirus A16 (B) infection, southern Vietnam, 2005.

Figure 5

Dendrogram constructed by using the neighbor-joining method (25) showing the genetic relationships between 23 human enterovirus 71 (HEV71) strains isolated in southern Vietnam during 2005 (underlined), based on the alignment of complete VP1 gene sequences. Branch lengths are proportional to the number of nucleotide differences. The bootstrap values in 1,000 pseudoreplicates for major lineages within the tree are shown as percentages. The marker denotes a measurement of relative phylogenetic distance. Strain names indicate a unique numerical abbreviation of country and year of isolation. Asterisks (*) denote HEV71 isolates obtained from fatal cases. The prototype coxsackievirus 16 (CVA16)–G10 strain (28) was used as an outgroup. The dendrogram shows genogroups A, B, and C as identified by Brown et al. (24). Details of the strains used to prepare the dendrogram are shown in Table 1.