Association of Human Metapneumovirus With Radiologically Diagnosed Community-Acquired Alveolar Pneumonia in Young Children
Wolf DG, Greenberg D, Shemer-Avni S, et al
J Pediatr. 2010;156:115-120
Study Summary
The investigators reviewed the growing understanding of the contribution of human metapneumovirus (HMPV) to lower respiratory tract infections, bronchiolitis, and viral pneumonias. Previous investigators have noted that vaccination with pneumococcal vaccine lowered the rates of HMPV isolation in patients with pneumonia, suggesting that bacterial pneumonia and viral lower respiratory tract infection often occur together. This study was designed to determine the frequency of viral coinfection when children are diagnosed with community-acquired alveolar pneumonia (CAAP, presumably a bacterial process). The participants were enrolled from 2001 to 2005 in Israel, before the introduction of pneumococcal conjugate vaccine. They were all younger than 5 years of age, were enrolled at a single hospital, and had alveolar pneumonia established by standard criteria (dense opacity on radiograph). The investigators obtained nasal wash specimens, including some from healthy controls, and tested for viruses via immunofluorescent assay, culture, and polymerase chain reaction (PCR). In addition to clinical and demographic data, the researchers obtained chest x-rays all participants. The x-rays were read by 3 individuals masked to patient identity or diagnosis. During the study period, the researchers obtained nasopharyngeal wash specimens from roughly 37% (n = 1296) of the children diagnosed with CAAP and from 137 normal controls.
Most patients diagnosed with CAAP (77%) were hospitalized for this illness. A viral pathogen was also identified in 46.9% of patients diagnosed with CAAP. Respiratory syncytial virus (RSV) was the most commonly isolated virus, found in 23.1% of patients with CAAP (roughly half of those in whom a virus was identified). HMPV was isolated in 8.3% of the study children but in just over 2% of controls. In 22% of the study children, a second virus was isolated. HMPV was isolated with a frequency equal to that of RSV in children older than 2 years. Finally, the frequency of HMPV (8.3%) was more than twice that of adenovirus, influenza, or parainfluenza (all < 3.5%). Although HMPV was isolated less often than RSV, patients with CAAP plus HMPV were more likely to have wheezing or gastrointestinal symptoms than patients who had CAAP plus RSV (Table). However, children with CAAP plus HMPV were 20% less likely to be admitted to the hospital than children with CAAP plus RSV. The investigators concluded that HMPV plays an important role in CAAP in childhood.
Table. Comparative Frequency of Symptoms
| Diagnosis | Gastrointestinal Symptoms | Wheezing |
|---|---|---|
| CAAP plus HMPV | 56.3% | 47.5% |
| CAAP plus RSV | 31.2% | 23.2% |
CAAP = community-acquired alveolar pneumonia; HMPV = human metapneumovirus; RSV = respiratory syncytial virus
Viewpoint
This is one of several studies showing that HMPV is isolated more often than any other virus save RSV in children with viral lower respiratory tract infection or pneumonia and that the relative isolation frequencies are qualitatively similar (RSV is most common, followed by HMPV, and then all others). It is not possible to know how many of the CAAP episodes represented a virus-caused focal infiltrate vs a true viral and bacterial coinfection, but there seems to be a significant correlation. There is biologic plausibility for coinfection to be a significant contributor to what we classically consider bacterial pneumonia in that many of these respiratory viruses impede airway clearance.
Abstract