Parainfluenza virus (PIV) infection among 3411 HSCT recipients, 1991–1999.

PIV was isolated from 253 patients (7.4%) during the study period (see text). Sporadic PIV-1, -2, and -4 (░) cases occurred primarily during the winter and spring; PIV-3 (▪) cases occurred year-round, as either sporadic disease or within “outbreaks.” The majority of outbreak cases were community acquired.