Rationale: Community-acquired pneumonia should be considered, with S. pneumoniae being the most common, although the lack of a productive cough makes it less likely. The remainder of the pathogens generally cause atypical pneumonia and are often similar to each other in presentation. L. pneumophila and influenza often present with severe headache in addition to respiratory symptoms. RSV and adenoviruses do not usually cause severe disease in adults; neither do Chlamydia nor Mycoplasma. The presence of significant hypoxia is worrisome, and contact with a possible communicable lower respiratory disease while taking care of a symptomatic patient makes the similar diagnosis likely.