An observational cohort study of bronchoalveolar lavage fluid galactomannan and Aspergillus culture positivity in patients requiring mechanical ventilation.

RATIONALE: Critically ill patients who develop invasive pulmonary aspergillosis (IPA) have high mortality rates despite antifungal therapy. Diagnosis is difficult in these patients. Bronchoalveolar lavage (BAL) fluid galactomannan (GM) is a helpful marker of infection, although the optimal cutoff for IPA is unclear. We aimed to evaluate the BAL fluid GM and fungal culture results, demographics, and outcomes among a large cohort of mechanically ventilated patients with suspected pneumonia.

METHODS: A single-center cohort study of patients enrolled in the Successful Clinical Response in Pneumonia Therapy (SCRIPT) study from June 2018 to March 2023. Demographics, BAL results, and outcomes data were extracted from the electronic health record and compared between groups of patients who grew Aspergillus on a BAL fluid culture, those who had elevated BAL fluid GM levels (defined as >0.5 or >0.8) but did not grow Aspergillus on BAL fluid culture, and those with neither.

RESULTS: Of over 1700 BAL samples from 688 patients, only 18 BAL samples grew Aspergillus . Patients who had a BAL sample grow Aspergillus (n=15) were older (median 71 vs 62 years, p=0.023), had more days intubated (29 vs 11, p=0.002), and more ICU days (34 vs 15, p=0.002) than patients whose BAL fluid culture was negative for Aspergillus (n=672). The BAL fluid galactomannan level was higher from samples that grew Aspergillus on culture than those that did not (median ODI 7.08 vs 0.11, p<0.001), though the elevation of BAL fluid GM varied across BAL samples for patients who had serial sampling. Patients who grew Aspergillus had a similar proportion of underlying immunocompromise compared with the patients who did not, and while no statistically significant difference in overall unfavorable outcome, had longer duration of ventilation and longer ICU stays.

CONCLUSIONS: In this large cohort of critically ill patients with a high number of BAL samples with GM levels, we found a relatively low rate of Aspergillus growth. Patients who eventually grew Aspergillus had inconsistently elevated BAL fluid GM, and many patients with elevated BAL fluid GM did not grow Aspergillus . These data suggest that the pre-test probability of invasive pulmonary aspergillosis should be considered low in a general ICU population undergoing BAL evaluation to define the etiology of pneumonia. Improved scoring systems are needed to enhance pre-test probability for diagnostic test stewardship purposes.