Hospital-acquired and ventilator-associated pneumonia Quiz: Ace Your Exams

An 82-year-old woman is admitted to the hospital for fractures of the left, 5th and 6th ribs after a fall at home. The fractures are minimally displaced and no surgical intervention is performed. The patient is provided with pain control and encouraged to use an incentive spirometer. On the third day of hospitalization, the patient becomes short of breath, febrile, and develops a nonproductive cough. Temperature is 38.5°C (101.3°F), blood pressure is 135/75 mmHg, pulse is 105/min, respiratory rate is 22/min, and oxygen saturation is 88% on room air. She is placed on 2L oxygen via nasal cannula. On physical examination, she appears ill, has labored breathing, and has rales in the left lower lung field. There is tenderness over the left 5th and 6th ribs, but the surrounding skin is unremarkable. She has no lower extremity swelling. Relevant laboratory studies are obtained and results are shown below. Chest x-ray demonstrates a new left lower lobe consolidation. What is the best next step in the diagnostic workup?
 

Laboratory Value	Result
Leukocyte count	15000/mm3
Neutrophils, segmented	78%
Neutrophils, banded	5%
Procalcitonin	0.75 ng/mL
D-dimer	< 500 ng/mL