[Human parainfluenza virus infections in infants and young children with acute respiratory infections in Beijing].
To understand the impact of human parainfluenza virus (HPIV) on acute respiratory infections in infants and young children in Beijing. Multiplex reverse transcription-PCR was used to amplify the hemagglutinin (HA) gene fragment of HPIV from clinical specimens. Primer pairs derived from a conserved region of the HA genes of HPIV were used to develop the multiplex RT-PCR for detecting and typing HPIV. The sensitivity and specificity of the method were determined by using various RNA and DNA viruses as controls. Specimens collected from 3519 children with acute respiratory infections from Aug. 2003 to Apr. 2006 were analyzed for HPIV by the multiplex RT-PCR as well as for other respiratory viruses by virus isolation and/or indirect immunofluorescent assay (IFA). Ten amplicons with expected molecular weight matching different types of HPIV were randomly selected for sequence analysis. Only the cDNA from the isolated strains of HPIV 1 and 3 was positive by the multiplex RT-PCR. Phylogenetic analysis for those 10 amplicons' sequences which belong to HPIV 1 - 4 types respectively as determined by multiplex-PCR indicated that these specimens were truly HPIV positive. These 10 HPIV positive specimens included two specimens of type 4 which was further subtyped as HPIV4A and 4B by sequence analysis. With the multiplex RT-PCR, HPIV were detected in 349 out of 3519 specimens with the positive rate of 9.9% (349/3519), which is higher than 4.8% by the methods of virus isolation and/or IFA. And the HPIV positive rates were high in patients with not only acute upper but also lower respiratory tract infection. No regular seasonality distribution of HPIV infection was found. HPIV 1 and 3 were more common than HPIV 2 and 4. With higher sensitivity and specificity than virus isolation and IFA, multiplex RT-PCR is beneficial for the etiologic and epidemiologic studies on HPIV, as well as for HPIV typing. The data from this study indicate that HPIV is one of the important etiological viruses of acute respiratory tract infections in infants and young children in Beijing.