Lower airway sampling greatly increases detection of respiratory viruses in critically ill patients: the COURSE study

Introduction

The prevalence of viral respiratory infections in critically ill patients on the ICU and the diagnostic potential of tracheal aspirate sampling are unknown. For this study, the prevalence of respiratory viruses was investigated in intubated patients by simultaneous sampling of nasopharynx and tracheal aspirate.

Methods

During March and April 2013, consecutive acutely admitted, intubated patients were included in three ICUs in the Netherlands, regardless of diagnosis at admission. Daily sampling of the nasopharynx (NP) with flocked swab and tracheal aspirate (TA) was performed until successful weaning from mechanical ventilation or death. Admission samples were tested via multiplex RT-PCR for influenza A and B, parainfluenza, RSV, human metapneumovirus, bocavirus, coronavirus, rhinovirus, enterovirus, parechovirus and adenoviruses. Of the influenza-positive patients, subsequent daily samples were tested for influenza. Results of viral diagnostics performed by routine care were collected, and compared with results found in this study.

Results

As part of an ongoing observational study (COURSE study), 128 patients were included, of which 35 were virus-positive (27%). Of these, 13 patients were positive in both NP and TA, eight only in NP, and 14 only in TA. Thereby, 40% of the viruses would have been missed if only NP was performed in this study group. In eight out of 12 coronaviruspositive patients, only the TA sample was virus-positive, with negative NP. In subsequent daily samples of influenza-positive patients, viral loads were higher in TA compared with NP, up to 2 log viral copies. Duration of positivity of influenza in daily samples was up to two times longer in TA samples than in NP samples. Of all 35 virus-positive patients, 10 had received viral diagnostics via routine care.

Conclusion

The prevalence of respiratory viruses in this unselected patient population is high. Forty percent would have been missed if only NP was sampled. Thereby, TA sampling adds to the detection of respiratory viruses in critically ill patients. Accuracy and implications of these results needs to be investigated further.