• A retrospective analysis of the PROSPECT trial identifies key factors affecting patient enrollment in a study of probiotics for critically ill, mechanically ventilated patients.
• Delayed initiation after regulatory approval and later engagement in the trial were associated with lower monthly enrollment rates per site.
• Sites with more experienced research coordinators demonstrated a trend towards higher patient enrollment, though not statistically significant.
• The PROSPECT trial found that Lactobacillus rhamnosus GG did not reduce the risk of ventilator-associated pneumonia or other infections.