Human metapneumovirus (hMPV) is a newly discovered paramyxovirus that causes acute respiratory illness. Despite apparent near-universal exposure during early childhood, immunity is transient.
An indirect screening ELISA using a recombinant, soluble, fusion (F) glycoprotein derived from hMPV was used to test for anti-F IgG in 1,380 acute and convalescent sera collected from children in Kamphaeng Phet, Thailand
1,376 (99.7%) tested sera showed evidence of prior infection with hMPV. 67 children demonstrated a four-fold or greater rise in titer for an overall re-infection rate of 4.9%. Two children demonstrated evidence of an initial infection. 49 of the 69 new or re-infections occurred in 2000, accounting for 13.2% of all non-flaviviral febrile illnesses in the study population in that year. Of 69 positive cases, 89.9% reported a respiratory symptom compared to 69.2% of tested negative cases (p<.001). All positive specimens were also tested for an increase in titer to RSV F and 27% exhibited a four-fold or greater rise in titer.
These results demonstrate hMPV reinfection causing illness at rates equal to that seen for initial infections. hMPV may represent a more significant impact in older children than previously realized and may be the cause of significant outbreaks.