We examined the impact of microbiological results from respiratory samples on choice of antibiotic therapy in patients treated for hospital-acquired pneumonia (HAP) or ventilator-associated pneumonia (VAP).

Four-year retrospective study.

Veterans’ Health Administration (VHA).

VHA patients hospitalized with HAP or VAP and with respiratory cultures between October 1, 2014, and September 30, 2018.

We compared patients with positive and negative respiratory culture results, assessing changes in antibiotic class and Antibiotic Spectrum Index (ASI) from the day of sample collection (day 0) through day 7.

Between October 1, 2014, and September 30, 2018, we identified 5,086 patients with HAP/VAP: 2,952 with positive culture results and 2,134 with negative culture results. All-cause 30-day mortality was 21% for both groups. The mean time from respiratory sample receipt in the laboratory to final respiratory culture result was longer for those with positive (2.9 ± 1.3 days) compared to negative results (2.5 ± 1.3 days; P < .001). The most common pathogens were Staphylococcus aureus and Pseudomonas aeruginosa. Vancomycin and β-lactam/β-lactamase inhibitors were the most commonly prescribed agents. The decrease in the median ASI from 13 to 8 between days 0 and 6 was similar among patients with positive and negative respiratory cultures. Patients with negative cultures were more likely to be off antibiotics from day 3 onward.

The results of respiratory cultures had only a small influence on antibiotics used during the treatment of HAP/VAP. The decrease in ASI for both groups suggests the integration of antibiotic stewardship principles, including de-escalation, into the care of patients with HAP/VAP.