Nosocomial transmission of echovirus 30: molecular evidence by phylogenetic analysis of the VP1 encoding sequence

Abstract

We investigated six cases of enterovirus infection in a neonatal unit. The index patient, a 5-day-old boy, was admitted with aseptic meningitis due to echovirus 30 (E30). Secondary infections with E30 occurred in five babies. Comparison of the complete VP1 sequences showed that the isolates recovered from the index patient and his mother were closely related to those recovered from the five babies with secondary infections, demonstrating a nosocomial transmission of the virus. In the phylogenetic tree reconstructed from the VP1 sequences, the isolates formed a monophyletic cluster related to an E30 strain collected in June 1997 during an outbreak of aseptic meningitis.

FIG. 1

Genetic relationships in E30 VP1 sequences for virus isolates recovered during a nosocomial outbreak. Pairwise maximum likelihood distances were estimated from the complete VP1 sequences (876 nucleotides). To account for nucleotide substitutions, Tamura-Nei's model (24) was used with a gamma distribution of rate heterogeneity across sites (transition/transversion ratio, κ = 8.47; shape parameter for gamma distribution, α = 0.3). To ensure phylogenetic accuracy, parameters α and κ were estimated with the Tree-Puzzle computer program (22) from a data set containing 27 E30 VP1 sequences. Nucleotide frequencies estimated from the data set were as follows: 29.1% for A, 24.3% for C, 23.5% for G, and 23.1% for U. The tree was constructed by the quartet puzzling method. The reliability value (as a percentage) for internal branches indicates how often the corresponding cluster was found among the 10,000 intermediate trees. In 3,060 quartets analyzed, 367 (12.0%) were unresolved. Branch length was drawn to the indicated scale. The sequence of the Bastianni reference strain was used as an outgroup to root the tree. An asterisk indicates a reliability of 100%, estimated by the bootstrap method in the neighbor-joining tree (data not shown). The phylogenetic tree was edited with the Treeview program (19).