With this exception, most viral infections result from exposure of a nonimmune person to infected persons who are shedding the implicated virus. Alveoli may contain fibrin, mononuclear cells, and occasionally some neutrophils. In severe cases, there may be hyaline membranes. Characteristic intracellular viral inclusions may occur with adenovirus, CMV, respiratory syncytial virus, or varicella-zoster virus. Symptoms, Signs, and Diagnosis Viral infections of the lower airways include bronchitis, bronchiolitis, and pneumonia.
Most patients have headache, fever, myalgia, and cough, which usually produces mucopurulent sputum.
The most common finding on chest x-ray is interstitial pneumonia or peribronchial thickening. Lobar consolidation and pleural effusions are not common but may occur with bacterial superinfection. The diagnosis is supported by finding sparse bacteria and a dominance of monocytes on smears of sputum and by failing to recover a likely bacterial pathogen. Identification of the virus is usually difficult but may be important during outbreaks, among seriously ill patients, and for those with treatable viruses. A specific diagnosis in most viral respiratory infections requires recovery of the virus from throat washings or tissue, identification of typical inclusions in cytopathology or biopsy specimens, or serologic assays.