Quantitative versus qualitative cultures of respiratory secretions for clinical outcomes in patients with ventilator‐associated pneumonia
Abstract
Background
Ventilator‐associated pneumonia (VAP) is a common infectious disease in intensive care units (ICUs). The best diagnostic approach to resolve this condition remains uncertain.
Objectives
To evaluate whether quantitative cultures of respiratory secretions are effective in reducing mortality in immunocompetent patients with VAP, compared with qualitative cultures. We also considered changes in antibiotic use, length of ICU stay and mechanical ventilation.
Search methods
We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2007, issue 4), which contains the Acute Respiratory Infections Group's Specialized Register; MEDLINE (1966 to December 2007); EMBASE (1974 to December 2007); and LILACS (1982 to December 2007).
Selection criteria
Randomized controlled trials (RCTs) comparing respiratory samples processed quantitatively or qualitatively, obtained by invasive or non‐invasive methods from immunocompetent patients with VAP, and which analyzed the impact of these methods on antibiotic use and mortality rates.
Data collection and analysis
Two review authors independently reviewed and selected trials from the search results, and assessed studies for suitability, methodology and quality. We analyzed data using Review Manager software. We pooled the included studies to yield the risk ratio (RR) for mortality and antibiotic change with 95% confidence intervals (CI).
Main results
Of the 3931 references identified from the electronic databases, five RCTs (1367 patients) met the inclusion criteria. Three studies compared invasive methods using quantitative cultures versus non‐invasive methods using qualitative cultures, and were used to answer the main objective of this review. The other two studies compared invasive versus non‐invasive methods, both using quantitative cultures. All five studies were combined to compare invasive versus non‐invasive interventions for diagnosing VAP. The studies that compared quantitative and qualitative cultures (1240 patients) showed no statistically significant differences in mortality rates (RR = 0.91, 95% CI 0.75 to 1.11). The analysis of all five RCTs showed there was no evidence of mortality reduction in the invasive group versus the non‐invasive group (RR = 0.93, 95% CI 0.78 to 1.11). There were no significant differences between the interventions with respect to the number of days on mechanical ventilation, length of ICU stay or antibiotic change.
Authors' conclusions
There is no evidence that the use of quantitative cultures of respiratory secretions results in reduced mortality, reduced time in ICU and on mechanical ventilation, or higher rates of antibiotic change when compared to qualitative cultures in patients with VAP. Similar results were observed when invasive strategies were compared with non‐invasive strategies.
PICOs
Plain language summary
Quantitative versus qualitative cultures of respiratory secretions for clinical outcomes in patients with ventilator‐associated pneumonia
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 ICU patients. The best method of diagnosing VAP and identifying the causative organism (bacteria) is not certain. Both invasive and non‐invasive techniques are used to obtain samples of respiratory secretions and these can be analyzed quantitatively (with a threshold count of the bacterial growth to differentiate between infection and colonization 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 colonizing organisms (those with lower concentration), thereby optimizing antibiotic therapy.
Until now, there has been no clear evidence to determine whether quantitative cultures are associated with better clinical outcomes than qualitative ones. Evidence from the 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.
