Prospective study of human metapneumovirus infection: diagnosis, typing and virus quantification in nasopharyngeal secretions from pediatric patients.

Study design: During the winter-spring seasons 2004-2005 and 2005-2006, 965 nasopharyngeal aspirates from 871 patients were examined for human metapneumovirus (hMPV) by both monoclonal antibodies (MAbs) and reverse transcription (RT)-PCR. Results: Overall, 46 samples (4.8%) from 37 patients were positive for hMPV. Of these, 39 were positive by RT-PCR, and 35 by MAbs. Thus, using RT-PCR as a reference assay, the sensitivity, specificity, positive and negative predictive values of MAbs were 71.8%, 99.2%, 80.0% and 98.8%, respectively. Typing showed that concordant results were obtained in 32/46 (69.6%) strains (five untyped), whereas three strains were typed by MAbs only, and I I by RT-PCR only. Finally, quantification of hMPV RNA allowed to correlate high viral load in nasopharyngeal secretions with acute respiratory symptoms in a group of I I infants with acute lower respiratory tract infection examined upon admission and discharge from hospital, and a group of nine infants examined upon admission only. Conversely, hMPV etiology was questioned in a group of 14 infants with low viral load. Conclusions: MAbs may represent an alternative to or a complement to RT-PCR for detection and typing of hMPV strains, while hMPV RNA quantification may help in associating viral load with clinical symptoms.