1. Presented by Robert Kruse, MD, PhD and reviewed by Karen Carroll, MD

Case vignette

A young adult with past medical history of psoriasis, treated using infliximab, presents with fever, cough, and congestion. The patient recently returned from living in a community-style housing arrangement. There, the patient was given antibiotics for presumed community-acquired pneumonia. Unfortunately, the patient's condition continued to worsen despite therapy. The patient is eventually admitted to the MICU with progressive chest infiltrates and multi-organ failure. Chest x-ray shows increased opacities within the lungs, most prominent within the lower lung fields, suggesting multifocal pneumonia. A small, pleural effusion was also noted. Bronchoalveolar lavage (BAL) was performed to facilitate diagnosis of an infectious etiology. Gram stain of the BAL, however, showed moderate polymorphonuclear cells (PMNs) with no organisms. A respiratory panel was ordered on a nasal swab (results currently pending), and consideration was made for how to prioritize viral testing on the BAL specimen.

Question:Which of the following viruses is the most likely cause of the severe presentation in this patient?