Molecular investigations of an outbreak of parainfluenza virus type 3 and respiratory syncytial virus infections in a hematology unit

Abstract

A large simultaneous outbreak of respiratory syncytial virus (RSV) and parainfluenza type 3 (PIV-3) infections occurred on an adult hematology unit. Implementation of enhanced infection control was complicated by cocirculation of the two different viruses, with prolonged viral shedding from infected patients, and placed great pressure on health care staff; of 27 infected hematopoietic stem cell transplant patients, 9 died, and the unit was closed for 2 months. Retrospective molecular investigation of the virus strains involved in the outbreak was performed by analyzing part of the fusion gene of PIV-3 and part of the glycoprotein gene of RSV. Reverse transcription-PCR on nasopharyngeal aspirates from patients infected before and during the simultaneous outbreak generated amplicons for sequence analysis. A single strain of RSV and a single strain of PIV-3 had spread from person to person within the unit; 7 patients were infected with RSV, 22 were infected with PIV-3, and 4 were infected with both viruses. The PIV-3 outbreak had started at the beginning of August 3 months before the RSV outbreak; it had arisen when PIV-3 was introduced from the community by a patient and passed to another patient, who became chronically infected with the identical strain and, in spite of being nursed in isolation, was most likely the source from which widespread infection occurred in November. Had these early cases been linked to a common PIV-3 strain at the time of diagnosis, enhanced infection control precautions might have prevented the eventual extensive spread of PIV-3, making it much easier to deal with the later RSV outbreak.

FIG. 1.

Incidence of PIV-3 and RSV infections on the hematology unit from August 1999 to January 2000. The vertical scale indicates the number of positive patients; the arrow indicates identification of the outbreak. Line 1, duration of stay of patient Q1 on the unit with laboratory-confirmed shedding of PIV-3. Line 2, duration of stay of patient Q2 on the unit. Line 3, duration of laboratory-confirmed shedding of PIV-3 by patient Q2. •, PIV-3 detected in NPA.

FIG. 2.

Sequence alignments for PIV-3 amplicons (nucleotide positions 61 to 296 of PIV-3; accession number X05303). Nucleotides are numbered with respect to the ATG translation start codon (shaded) of the F gene (5′ noncoding region, −153 to 0; open reading frame, +1 to +75). Note that in the UCH outbreak strain there is another translation start codon (shaded) (see text for discussion). Abbreviations: UCH, amplicons from hematology unit inpatients in 1999 (OB1 to -23, Q1, Q2, and Q5); P-X, amplicon from PX, a hematology outpatient infected with PIV-3 in 1999; P-1 to P-3, amplicons from three hematology inpatients infected with PIV-3 in 2000; P4 and P5, amplicons from two children infected with PIV-3 in 1999; Wash, amplicon from PIV-3 reference strain Wash/47885/57.

FIG. 3.

Phylogenetic tree based on sequence alignments of the PIV-3 amplicons shown in Fig. 2. The scale bar indicates the relative genetic distance according to the Jukes-Cantor algorithm. Abbreviations: UCH, amplicons from hematology unit inpatients in 1999 (OB1 to -23, Q1, Q2, and Q5); P-X, amplicon from PX, a hematology outpatient infected with PIV-3 in 1999; P-1 to P-3, amplicons from three hematology inpatients infected with PIV-3 in 2000; P4 and P5, amplicons from two children infected with PIV-3 in 1999; Wash, amplicon from PIV-3 reference strain Wash/47885/57.

FIG. 4.

Sequence alignments for RSV amplicons (nucleotide positions 651 to 918 of RSV [268 nucleotides from glycoprotein G]; accession number Z33430). Abbreviations: UCH, amplicons from hematology unit inpatients in 1999 (OB20 to -30; A-1 to A-7, amplicons from control patients A1 to A7. Ten representative sequences for RSV subtypes A and B selected from GenBank are indicated by their accession numbers.

FIG. 5.

Phylogenetic tree based on the sequence alignments of RSV amplicons and representative sequences for RSV subtypes A and B selected from GenBank, as shown in Fig. 4. The scale bar indicates relative genetic distance according to the Jukes-Cantor algorithm. Abbreviations: UCH, amplicons from hematology unit inpatients in 1999 (OB20 to -30); A-1 to A-7, amplicons from control patients A1 to A7.