Association between high nasopharyngeal viral load and disease severity in children with human metapneumovirus infection

BACKGROUND: Previous studies have shown that viral genotype and viral load may play a significant role in the pathogenesis of viral infections. OBJECTIVES: The aim of this study was to evaluate these aspects of hMPV infections in children and their household contacts. STUDY DESIGN: Between 1 November 2003 and 31 March 2004, we prospectively studied 2060 children attending our Emergency Department for acute reasons. Nasopharyngeal swabs were collected upon enrolment and then tested with real-time PCR assays for the major viral causes of respiratory illness. RESULTS: Sixty children (2.9%) were infected by hMPV: 24 (1.2%) by hMPV A, 14 (0.7%) by hMPV B, 11 (0.5%) by untyped hMPV, and 11 (0.5%) by hMPV and an additional respiratory virus. There were no differences in disease presentation or in clinical or socioeconomic impact in relation to viral genotypes. HMPV viral load was significantly higher in children with lower respiratory tract involvement (p < 0.05), hospitalised children (p < 0.05), and the prevalence of secondary cases of a similar disease in the household of index cases (p < 0.05). CONCLUSION: A high hMPV viral load correlated with disease presentation, whereas the overall clinical and socioeconomic burden caused by the two hMPV genotypes was similar.