Evidence of human metapneumovirus in Australian children

To the Editor: We wish to report the identification of a novel virus causing lower respiratory tract disease in Australian children. The presence of this virus was recently described in Dutch children and tentatively called human metapneumovirus (hMPV).1 Clinical symptoms of infection are reported to resemble those of human respiratory syncytial virus (hRSV) infection. We therefore investigated whether the virus was present in Australian children.

Three isolates were identified from a random selection of 200 nasopharyngeal aspirate (NPA) specimens collected throughout 2001 from children presenting to the Royal Children's Hospital, Brisbane, or the Logan Hospital, a public hospital to the south of Brisbane, with clinical respiratory tract disease. All NPA specimens were initially negative for hRSV, influenza A and B, parainfluenza 1, 2 and 3 and adenovirus by direct fluorescent antigen testing and subsequent viral culture. These negative NPA specimens were then screened by polymerase chain reaction (PCR) for hMPV, based on the known sequence of the virus.2 Sequencing of the PCR product in all three positive samples was 100% homologous with the known hMPV sequence. Viral growth was subsequently detected in culture from two of these samples, and confirmed as hMPV, using the method of van den Hoogen et al.1 Co-existent infection with coronavirus, rhinovirus, Bordetella pertussis, Chlamydia pneumoniae and Mycoplasma pneumoniae was excluded by PCR screening of the three hMPV isolates using validated in-house methods based on established protocols. Clinical features of the infected children are summarised in the Box.

This is the first report of the presence of hMPV infection in Australian children and describes a new viral respiratory syndrome. It also adds to the clinical spectrum and understanding of respiratory viruses causing acute bronchiolitis in children. Only 25%–33% of NPA specimens collected from our population with suspected respiratory tract disease yield a positive result for a known viral or bacterial pathogen. Clinical features in this small cohort are difficult to separate retrospectively from hRSV.

Based on the findings of this limited preliminary study of children presenting to hospital with respiratory tract symptoms, we would predict that hMPV is also relatively common in the Australian community. We are currently undertaking further characterisation of the hMPV isolates, a more detailed study of the epidemiology of hMPV disease, as well as developing improved diagnostic assays to rapidly identify clinical cases and assess seroprevalence of immunity to hMPV.