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

Of the pathogens investigated in this study, HPIVs were the sixth most frequently isolated. The predominant types were HPIV-3 and HPIV-1, which is consistent with previous reports [5] [6] [7] . HPIVs were isolated with higher frequency from males than females, similar to the previous study [21] . Immunity to HPIVs is incomplete, and infections occur throughout life [20] . In this study, HPIVs were detected in patients over a wide age distribution. However, many more children were infected than adults (p<0.001), and the vast majority of HPIV infections occurred in patients under 5 years of age. The four HPIV types differed in age distribution of patients infected. HPIV-3 was mainly detected in paediatric patients under 3 years old, while HPIV-1 and HPIV-2 were isolated from a broader age distribution than HPIV-3 ( Figure 1 ). No infant under one month of age was HPIV positive. These results are in accordance with seroprevalence studies indicating that newborn infants have high levels of HPIV antibodies, and that these levels decrease substantially by 7 to 12 months of age [20] . In this study, HPIV-4 was only detected in children (4 months to 8 years old). This result is different from previous studies in which fairly equal infection rates were reported among infants younger than one year old, preschool children, school age children and adults [14] [15] [16] [17] [18] . The low HPIV-4 positivity in our study may have influenced our results.