OBJECTIVESHuman metapneumovirus (hMPV) has been identified as one of the most important viral pathogens for acute respiratory tract infections in children. This study was to observe neutralizing activity to hMPV in sera collected from children without respiratory illnesses aged 0 to 6 years and to investigate the correlation between the level of hMPV IgG antibody and neutralizing activity in the same serum.

METHODSSera of 0 to 3 years old children were collected from patients hospitalized for surgery without documented respiratory illnesses, and sera of 3 to 6 years old children were remainder of serum specimens taken for health checkup. Total number of serum specimens was 325. Ten serum samples were selected for neutralizing activity detection in every age group and the sum was 50. The neutralizing titer was assessed by microneutralization assay which had been well documented previously.

RESULTSAmong 50 serum samples, eight in which hMPV IgG antibody was proved negative by ELISA previously did not show any neutralizing activity. The remaining 42 samples, as expected, showed variable neutralizing activity. The geometric mean neutralizing titer to hMPV for all the samples was 1:129. In the age group of 0-5 months, the geometric mean titer was 1:160. In the age groups of 6-11 months, 12-23 months, 24-35 months, 3-6 years, the geometric mean titers were 1:58.9, 1:114.9, 1:172.8 and 1:160.0, respectively. The level of hMPV antibody and neutralizing activity in the same serum was significantly correlated (r = 0.668).

CONCLUSIONMost 0-6 year-old children in Chongqing area have neutralizing antibody in their serum. Whether such neutralizing activity is high enough to prevent infection with different subtypes of hMPV is unknown.