Abstract & Commentary

Detecting Human Metapneumovirus in Young Children

By Hal B. Jenson, MD, FAAP, Professor of Pediatrics, Tufts University School of Medicine; Chief Academic Officer, Baystate Medical Center, Springfield, MA, is Associate Editor for Infectious Disease Alert.

Dr. Jenson reports no financial relationships relevant to this field of study.

Synopsis: Human metapneumovirus (HMPV) is an important cause of lower-respiratory tract infections among children, and is epidemiologically and clinically similar to respiratory syncytial virus (RSV). HMPV more frequently infects children older than 12-24 months of age, and is associated with a lower rate of hospitalization than RSV.

Source: Wolf DG, et al. Association of human metapneumovirus with radiologically diagnosed community-acquired alveolar pneumonia in young children. J Pediatr. 2010;156:115-120.

A prospective study from November 2001 through October 2005 in Israel collected nasopharyngeal wash specimens from children < 5 years who were diagnosed with community-acquired alveolar pneumonia. Alveolar pneumonia was defined radiographically as a dense opacity appearing as a fluffy consolidation, often containing air bronchograms and sometimes associated with pleural effusion, which is the standard of the Pneumonia Vaccine Trial Investigators' Group of the World Health Organization. Nasopharyngeal specimens were cultured for RSV, influenza A and B viruses, parainfluenza viruses, and adenoviruses by direct immunofluorescence assay. HMPV was detected by RT-PCR.

Of 3,507 children with community-acquired alveolar pneumonia, nasopharyngeal specimens were obtained from 1,296 (37%) children, including 997 who were hospitalized. A virus was detected in 608 (46.9%) children. RSV was the most common viral pathogen (23%), followed by HMPV (8.3%), adenovirus (3.4%), influenza A virus (2.9%), and parainfluenza viruses (2.9%). HMPV was identified in 84 children (6.5%) as a single viral pathogen and in 24 children (1.8%) as a co-pathogen, with RSV (10), adenovirus (4), RSV and adenovirus (3), RSV and influenza A virus (1), cytomegalovirus (3), influenza B virus (2), or parainfluenza virus type 3 (1).

Blood cultures were obtained in 3,160 children (90%), of which 42 (1.3%) were positive, including Streptococcus pneumoniae (29), Haemophilus influenzae (nontypable, 3; type b, 2; type a, 1), Enterococcus (2), Staphylococcus aureus (2), group A streptococcus (1), Brucella (1), and Neisseria meningitidis (1).

There was a clear seasonality with two annual peaks, a major winter peak from November through March, and a minor peak from April through June. During the winter peaks, respiratory viruses were detected in 550/1,017 specimens (54%). RSV was significantly more common than HMPV among children < 12 months of age (37% vs. 6.5%; p < 0.001). The predominance of RSV was still significant during the second year of life (14.7% vs. 5.4%; p < 0.001), with comparable proportions of RSV and HMPV during the third to fifth years of life. Children with HMPV were less likely to be hospitalized than those with RSV (76.2% vs. 93.3%; p = 0.005, adjusted for age).

Commentary

HMPV was discovered in 2001, and has been increasingly recognized as an important cause of lower respiratory tract infections among young children. In this study, it was detected in 8.3% of children diagnosed with community-acquired alveolar pneumonia, including 9.3% of those evaluated during seasonal peaks from November through May. In approximately one-quarter of cases, HMPV was identified as a co-pathogen with one or more other respiratory viruses.

Although there is general overlap of HMPV and RSV epidemiologically and clinically, children with HMPV were significantly older than those with RSV alveolar pneumonia. While RSV accounts for the majority of virus-associated alveolar pneumonia among children under 12 months of age, the burden of HMPV and RSV alveolar pneumonia was approximately equal among children 2-4 years of age. Perhaps because of the older age at the time of infection, children with HMPV alveolar pneumonia were also less likely to be hospitalized than those with RSV alveolar pneumonia.