Multicluster nosocomial outbreak of parainfluenza virus type 3 infection in a pediatric oncohematology unit: a phylogenetic study

Background Human parainfluenza virus type 3 (hPIV-3) has been reported to cause nosocomial outbreaks of respiratory infection, in particular among hematopoietic stem cell transplantation recipients. Design and Methods From September 2007 through January 2008 several episodes of hPIV-3 infection were observed among young patients followed at the Oncohematology Unit (OHU) or other units of the Pediatrics Department. In 32 young patients (median age 3.5 years, range 21 days-27 years), hPIV-3 infection was diagnosed by direct fluorescent antibody staining of cells from respiratory secretions, and virus quantified by real-time RT-PCR in nasopharyngeal aspirates or bronchoalveolar lavage samples. In addition, the epidemiologic relatedness of hPIV-3 strains was investigated by sequencing two variable regions of the hemagglutinin-neuraminidase gene (nt 1-569 and nt 762-1239). Results Of the 32 hPIV-3-positive patients, 19 were hematopoietic stem cell transplantation recipients, 8 had hematologic malignancies, and 5 were immunocompetent children. Sixteen patients had upper, and 16 lower respiratory tract infection. All patients but one had high viral load in nasopharyngeal aspirates (>1.0x10(6) RNA copies/mL). One patient died from respiratory failure with a high viral load in bronchoalveolar lavage. Phylogenetic analysis showed that 16/32 strains were identical. Besides this major cluster, three other clusters were identified, each one defining a smaller outbreak. Conclusions Phylogenetic analysis allows identification of the role of a single or multiple hPIV-3 strains in the person-to-person transmission within an outbreak occurring in clinical units.