The A2c variants of human metapneumovirus predominantly circulating in Qingdao, China, during 2018 and 2019.

Human metapneumovirus (HMPV) plays an important role in acute respiratory tract infections (ARTIs), especially in children. We investigated the epidemiology of HMPV associated with ARTIs among pediatric inpatients and identified HMPV genetic variations in Qingdao, China, from January 2018 to June 2019. HMPV-positive samples were identified from throat swabs by multiplex real-time reverse transcriptase polymerase chain reaction (RT-PCR). The G gene sequences of HMPV were obtained, followed by phylogenetic analysis. As a result, 71 out of 1051 (6.76%) patients were HMPV positive, and the HMPV-positive rate in children under 5 years of age was three times higher than that in those aged 5-17 years. The epidemic season of HMPV was in spring, with a peak mainly in March. Thirty-two nucleotide sequences of the HMPV G gene successfully obtained were clustered into three genotypes, A2c (25/32, 78.13%), B1 (3/32, 9.38%) and B2 (4/32, 12.50%). In addition, 76% (19/25) of A2c viruses were identified as the emerging A2c variants, which were predominantly circulating among pediatric inpatients with ARTIs between January 2018 and June 2019 in Qingdao. The emerging A2c variants have spread between countries and cities and might spread more widely in the future. Further prevalence monitoring of this duplication variant is needed to clarify the potentially expanding transmission and to provide a scientific basis for disease control and vaccine development.