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. 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). 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. 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.