Respiratory virome is an integral part of the human microbiome and its characterization may contribute to a better understanding of the changes that arise in the disease and, consequently, influence the approach and treatment of patients with acute lower respiratory infections.

The aim of this study was to evaluate the presence of respiratory viruses in the lower airways of individuals undergoing invasive mechanical ventilation, with and without acute lower respiratory infection (respectively WRI and WORI groups).

We studied 44 mini-bronchoalveolar lavage samples (collected with a double catheter, Combicath® kit) from patients with mean age in the seventh decade, 20 from WORI group and 24 from WRI group, who were hospitalized for acute respiratory failure in Intensive Care Units of two hospitals in the Lisbon area. Real-time PCR was applied to verify analyse the presence of 15 common respiratory viruses (adenovirus, human bocavirus, influenza virus A and B, repiratory syncytial virus, human parainfluenza virus types 1, 2, 3 and 4, human enterovirus, human rhinovirus, human metapneumovirus, human coronavirus group 1 (229E, NL63) and 2 (OC43, HKU1).

Respiratory viruses were detected in six of the 20 patients in the WORI group: influenza AH3 (n = 2), parainfluenza virus 1/3 (n = 2), human rhinovirus (n = 2), respiratory syncytial virus (n = 1) and human metapneumovirus (n = 1).

In the WRI group, respiratory viruses were detected in 12 of the 24 patients: influenza AH3 (n = 3), human rhinovirus (n = 3), respiratory syncytial virus (n = 3), human metapneumovirus (n = 3), human bocavirus (n = 2) and human enterovirus (n = 1). Simultaneous detection of two viruses was recorded in two samples in both groups.

The results of this study suggest the presence of common respiratory viruses in the lower respiratory tract without causing symptomatic infection, even in carefully collected lower samples. This may have important implications on the interpretation of the results on the diagnostic setting.