At present, hMPV has been recognized as one of the important pathogens of respiratory tract infection in the world. The diseases caused by hMPV are not significantly different from other viral infections, ranging from mild upper respiratory tract infection to severe bronchopneumonia. Most of the clinical manifestations were cough, runny nose, fever and wheezing. Hypoxemia occurred in about 1/3 of the patients. Chest X-ray showed local infiltrating shadow of pulmonary lobes or infiltration around hilar lung and peritracheal cuff sign. It is estimated that 4–16% of acute respiratory tract infections are caused by hMPV[22,23]. The virus has attracted wide attention at home and abroad since it was first identified in 2001. In 2003, Zhu Runan et al  first reported the infection of hMPV in China, and then similar reports were successively reported in other places in China [10-12]. However, there has been no research report on the infection of hMPV in Huzhou at present.
The onset of hMPV infection has a certain seasonality, with most reports suggesting that it occurs in winter and spring. In the northern hemisphere peak hMPV disease occurrence is typically in winter and spring months of January to May [24,25,26], while in the southern hemisphere peak prevalence is in the spring period of August to September . This study showed that there was a statistically significant difference in the detection rate of hMPV among the positive cases in different months. The main epidemic months were November and January-March, and the epidemic season was winter and spring, which was consistent with the results reported by Jin Yu . In addition, the results of this paper show that the hMPV detection rate was approximately in the years 2016–2019, but an apparent low frequency of circulation of hMPV in the year 2020, with a low positive rate of 1.79%, which may be related to factors such as the emergence of the local 2019-nCoV in February 2020 in Huzhou, the increased awareness of crowd protection, the reduction in crowd gathering, and the suspension of kindergarten and school.
Worldwide, hMPV prevalence in hospital inpatient or community studies, in children or elderly adults, varies widely from as low as 1.7% to as high as 17%, with generally higher prevalence in outpatients compared to inpatients and, also, more in children younger than 5 years compared to older age groups [28,29,30]. In this study, 1133 cases of children with severe acute respiratory tract collected in Huzhou from 2016 to 2020 were tested for hMPV nucleic acid, and 56 cases were detected positive, with a positive rate of 4.94%, indicating that hMPV is indeed one of the important pathogens causing severe acute respiratory tract infection in children in Huzhou. The total number of cases under 5 years old was 84.55%(958/1133), The number of positive cases was 85.71%(48/56); No significant difference was found between the two sexes in the infection of the virus, which was consistent with the report of Xu Meijia .
Studies have shown that two types of hMPV genotypes A and B can be prevalent together in the same season, and genotype A is the most prevalent. The prevalence pattern of hMPV genotypes in the same region may change continuously in different years. Liu Shiwen reported  that there were A2, B1 and B2 genotypes of hMPV prevalent in Jiangxi, among which A2 genotype was the dominant genotype. Our monitoring data showed there are A1, B1 and B2 genotypes of hMPV prevalent in Huzhou area. The B1 genotype strain was the most prevalent types and has been detected every year (except in 2020), followed by B2 and A1, so we speculated that the B1 genotype strain is the main epidemic strain in Huzhou area. However, the genotypes of the endemic strains are different from year to year, and one or several endemic types exist simultaneously every year, there are no type of hMPV presented absolutely predominant during hMPV epidemic seasons.
Our study is limited by a single-site setting, small sample size, and especially the partial genotyping of detected hMPV. Genotyping was only successful for 50%(28/56) of hMPV infection cases. In the future research, we will gradually improve the research content, expand the detection range and quantity of samples, accumulate and analyze data, further evaluate the harm of hMPV-related diseases, and provide more scientific basis for the prevention and control of infection of this virus.