An Observational Cohort Study of Bronchoalveolar Lavage Fluid Galactomannan and Aspergillus Culture Positivity in Patients Requiring Mechanical Ventilation.

Abstract

Background: Critically ill patients who develop invasive pulmonary aspergillosis (IPA) have high mortality rates despite antifungal therapy. Diagnosis is difficult in these patients and incidences vary in the literature. Bronchoalveolar lavage (BAL) fluid galactomannan (GM) is a helpful marker, although the optimal cutoff is unclear.

Methods: This was a single-center cohort study of patients requiring mechanical ventilation in the medical intensive care unit (ICU) from June 2018 to March 2023. Demographics, BAL, and outcome data were extracted from the electronic health record and compared between groups of patients who grew Aspergillus from BAL, those who had elevated BAL GM levels (>0.5, >0.8, or >1.0) but did not grow Aspergillus, and those with neither.

Results: Of >1700 BALs from 688 patients, only 18 BALs from 15 patients grew Aspergillus. Patients who grew Aspergillus had more intubated days (29 vs 11, P = .002) and more ICU days (34 vs 15, P = .002). BAL GM level was higher from samples that grew Aspergillus than those that did not (median optical density index: 7.08 vs 0.11, P < .001).

Conclusions: In this large cohort of critically ill patients, we found a low rate of Aspergillus growth and variable BAL GM elevation. These data suggest that the pretest probability of IPA should be considered low in a general ICU population undergoing BAL evaluation to define the etiology of pneumonia. Elevated BAL GM may not reliably indicate invasive disease, but lack of culture positivity may also miss true infection. Improved scoring systems are needed to enhance pretest probability for diagnostic test stewardship purposes, and tests must be interpreted in their own clinical contexts.