An outbreak of enterovirus 71 infection in Taiwan, 1998. II. Laboratory diagnosis and genetic analysis

Background: An epidemic of enterovirus 71 (EV71) occurred in Taiwan from April to December of 1998, with two peaks, one in June and the other in October. Many enteroviruses were isolated in our laboratory from 258 cases during this outbreak. Approximately half of the enteroviruses isolated were EV71 and one fifth were coxsackievirus A16. Objectives: To analyze laboratory findings in the EV71 epidemic of 1998 in Taiwan, various EV71 specimens in different cell lines were examined. In addition, genetic analysis of 5′ non-coding region (NCR) was performed to analyze the strain variation in this outbreak. Results: The cytopathic effect induced by EV71 was observed 2–13 (mean of 4.5) days post-inoculation in Vero cells and 4–15 (mean of 6.6) days in green monkey kidney (GMK) cells inoculated with throat swabs. Of the total positive EV71 cases, virus was most frequently obtained from throat swabs (91.7%), less from stools (64.8%), and none from cerebral spinal fluid (CSF). Molecular analyses of EV71 by sequencing the 5′ NCR of 34 strains obtained from different clinical categories and various geographic areas showed that their sequences differed (0–13 bp in 681 bp sequenced) by ∼0–2%. The sequences of these isolates differed from EV71 prototype BrCr or MS strain by 17.5–19%, with the exception of two samples which exhibited nucleotide variation by only 8.9 and 8.2%, when compared to the MS strain. Conclusion: EV71 was most frequently isolated from throat swab specimens in Vero cells. The molecular analyses of the 5′ NCR of EV71 revealed that most isolates from this epidemic belonged to a group of closely related clones and only two were in a different group which was clustered with the EV71 MS strain.