Molecular epidemiology of two consecutive outbreaks of parainfluenza 3 in a bone marrow transplant unit

Abstract

Two consecutive nosocomial outbreaks of parainfluenza 3, in which 5 of 15 infected patients died, occurred in an adult bone marrow transplant unit. Parainfluenza 3 strain variation was assessed by reverse transcription-PCR sequencing of part of the parainfluenza 3 F gene, including the noncoding region, directly from clinical samples. Sequence data from the outbreaks were compared with those from 15 other parainfluenza 3 isolates circulating concurrently in the community; altogether, 13 strains which fell into three lineages were identified. Four immunosuppressed patients shed virus persistently for between 1 and 4 months without change in sequence. The first outbreak lasted 4 months and involved three parainfluenza 3 strains, and one persistently infected patient was implicated as the source of infection for three others. The second outbreak lasted for 1 month but involved only one strain. These data indicate that introduction of community parainfluenza 3 strains to the bone marrow transplant unit was followed by person-to-person transmission within the unit rather than reintroduction of virus from the community.

FIG. 1

Timing of PIV3 isolates from patients in outbreaks 1 and 2 in relation to the prevalence of PIV3 in England and Wales. The data for the laboratory isolates are derived from reports made to the Public Health Laboratory Service Communicable Disease Surveillance Centre and are shown as a histogram. The timing of the outbreaks and the length of shedding of PIV3 by different patients (P1 to P15) are indicated. Symbols: •, clinical sample sequenced; ★, PIV3 detected, but insufficient material for sequence; †, patient died; W, patient’s ward.

FIG. 2

(a) Sequence analysis of community control PIV3 isolates and patient samples. Nucleotides are numbered with respect to the AUG start codon of the F gene (18). (b) Phylogenetic tree of the 237-bp region of the F gene showing relationships between outbreak strain sequences and control community PIV3 isolate sequences. The scale beneath the tree shows the percentage diversity between the sequences.

FIG. 2

(a) Sequence analysis of community control PIV3 isolates and patient samples. Nucleotides are numbered with respect to the AUG start codon of the F gene (18). (b) Phylogenetic tree of the 237-bp region of the F gene showing relationships between outbreak strain sequences and control community PIV3 isolate sequences. The scale beneath the tree shows the percentage diversity between the sequences.