Here is the microscopic appearance of a viral pneumonia with interstitial lymphocytic infiltrates. Note that there is no alveolar exudate. Thus, the patient with this type of pneumonia will probably not have a productive cough. The most common causes for viral pneumonia are influenza, parainfluenza, adenovirus, and respiratory syncytial virus (RSV appears mostly in children). Cytomegalovirus can appear in immunocompromised hosts.

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