Human Metapneumovirus and Human Coronavirus NL63

Abstract

To the Editor.—We read with great interest the article by Lambert et al that studied the role of 2 new respiratory viruses (human metapneumovirus [hMPV] and human coronavirus NL63 [hCoV-NL63]) in healthy preschool-aged children using parent-collected specimens with molecular techniques.1 The study showed that these viruses circulated in Melbourne, Australia, during 2003, and an association between child care and acute respiratory illness was proposed.1 We believe that some methodologic aspects of this study may have impaired the accuracy of the assessment of the role of these 2 viruses in such a population. Current literature shows that there are differences between respiratory samples collected by nose/throat swabs and nasopharyngeal aspirates regarding their potential to detect and identify respiratory pathogens.2 Tracheal secretion is less suitable for detection of respiratory viruses than nasopharyngeal washes and bronchoalveolar lavage.2 Another important point is the classification of symptoms, based entirely on parental experience. There are many subjective signs that, for an inexperienced person, would be difficult to recognize. All conclusions of an association between acute respiratory illness and virus incidence are based on symptom classifications (A and B), which may be incorrect.Finally, different methods were used to determine the incidence of several respiratory viruses. It has been shown that the sensitivity and specificity of real-time polymerase chain reaction (PCR), conventional PCR, and nested PCR may be completely different. In this case, hMPV and hCoV-NL63 were identified by using the most sensitive techniques (real-time and nested PCR), which might lead to an overestimation of the role of hMPV and hCoV-NL63 in community-acquired infections. However, there are no gold standards for detection of respiratory viruses to which both conventional tests and real-time PCR can be compared.3