Epidemiology and clinical presentation of the four human parainfluenza virus types

Liu, Wen-Kuan; Liu, Qian; Chen, De-Hui; Liang, Huan-Xi; Chen, Xiao-Kai; Huang, Wen-Bo; Qin, Sheng; Yang, Zi-Feng; Zhou, Rong

Biennial fall epidemics of HPIV-1 have been reported in previous studies [2, 7, 13, 23] . HPIV-2 has been reported to cause infections biennially with HPIV-1, to alternate years with HPIV-1, or to cause yearly outbreaks [7, 24, 25] . HPIV-3 is reported to have occurred annually during April to June in the United States [2] . Only a small number of studies have studied the epidemiology of HPIV-4, and the numbers of infections were too low to clearly identify seasonal peaks in activity [2, [14] [15] [16] [17] [18] . In this study, HPIVs were isolated throughout the year. Seasonal peaks of HPIVs, driven mostly by HPIV-3 and HPIV-1, occurred in the time when autumn turned to winter and summer turned to autumn (September 2009 to November 2009; September 2010 to October 2010; April 2011 to July 2011). These results differ from previous reports [2, 7, 13, 23] . In addition, HPIV-3 and HPIV-1 did not show the competitive interaction described previously, where HPIV-3 activity appeared to be greater during years when HPIV-1 was not circulating [2] . The different geographic location might lead to the different seasonal distributions of HPIVs. HPIV-2 and HPIV-4 were not isolated as frequently as HPIV-3 and HPIV-1, and the seasonal peak of HPIV-2 and HPIV-4 was in the turn of winter to spring (December 2010 to March 2011). The frequency of detection of these two HPIV types increased when detection of HPIV-3 and HPIV-1 declined.