An observational cohort study of bronchoalveolar lavage fluid galactomannan and 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 on a BAL fluid culture, those who had elevated BAL fluid GM levels (defined as >0.5 or >0.8) but did not grow on BAL fluid culture, and those with neither.

RESULTS

Of over 1700 BAL samples from 688 patients, only 18 BAL samples grew . Patients who had a BAL sample grow (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 (n=672). The BAL fluid galactomannan level was higher from samples that grew 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 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 growth. Patients who eventually grew had inconsistently elevated BAL fluid GM, and many patients with elevated BAL fluid GM did not grow . 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.