Ventilator-associated pneumonia (VAP) is a condition which occurs in patients mechanically-ventilated for more than 48 hours and can significantly increase the mortality of intensive care unit (ICU) patients. The best method for diagnosing VAP and identifying the causative organism (bacteria) is uncertain. Both invasive and non-invasive techniques are used to obtain samples of respiratory secretions and these can be analysed quantitatively (with a threshold count of the bacterial growth to differentiate between infection and colonisation of the lower airways) or qualitatively (presence or absence of pathogenic germs in the culture). The rationale for using quantitative cultures of respiratory secretions sampled from patients with VAP is to differentiate the infectious organisms (those with a higher concentration) from colonising organisms (those with lower concentration), thereby optimising antibiotic therapy.
Until now, there has been no clear evidence to determine whether quantitative cultures are associated with better clinical outcomes than qualitative ones. Three studies (1240 patients) were included comparing invasive methods using quantitative cultures, versus the non-invasive method using qualitative cultures. Two additional studies (127 patients) compared invasive versus non-invasive methods, both using quantitative cultures. All five studies (1367 patients) were combined to compare invasive versus non-invasive interventions for diagnosing VAP.
Evidence from trials included in this review indicates that there is no clinical advantage in the use of quantitative over qualitative cultures, nor in using invasive over non-invasive diagnostic approaches.