Human metapneumovirus reinfection among children in Thailand determined by ELISA using purified soluble fusion protein

Background. Human metapneumovirus (hMPV) is a newly discovered paramyxovirus that causes acute respiratory illness. Despite apparent near-universal exposure during early childhood, immunity is transient. Methods. An indirect screening enzyme-linked immunosorbent assay using a recombinant soluble fusion (F) glycoprotein derived from hMPV was used to test for anti-F IgG in 1380 pairs of acute- and convalescent-stage serum samples collected from children in Kamphaeng Phet, Thailand. Results. Of the 1380 serum sample pairs tested, 1376 (99.7%) showed evidence of prior infection with hMPV. Sixty-six paired specimens demonstrated a ≥4-fold rise in titer, for an overall reinfection rate of 4.9%. Two children demonstrated evidence of an initial infection. Forty-eight of the 68 new infections or reinfections occurred in 2000, accounting for 13.2% of all nonflaviviral febrile illnesses in the study population in that year. Of 68 positive cases, 85.3% complained of cough and 66.2% complained of rhinorrhea, compared with 61.4% and 49.0% of negative cases, respectively (P < .01). All positive samples were also tested for an increase in titer of antibodies to respiratory syncytial virus F, and 27% exhibited a ≥4-fold rise. Conclusion. These results demonstrate that hMPV reinfections cause illness at a rate equal to that seen for initial infections. hMPV may have a more significant impact in older children than previously realized and may be the cause of significant outbreaks in this population.