**4.1. Organisms that cause atypical pneumonias include**

*Mycoplasman pneumoniae*, the most common atypical pneumonia organism spreads when someone carrying the infection comes in close contact with others. The condition, also known as "walking pneumonia," is generally mild and seen in the outpatient setting. It appears to occur mostly in school-aged children and young adults. Less common is *Chlamydia pneumoniae* which causes 10% of all CAP cases and is usually mild but usually more severe in the elderly [31]. *Legionella pneumophila* causes Legionnaires' disease commonly found in hotels, cruise ships, hospitals and commercial buildings, where people come into contact with contaminated droplets from cooling towers and evaporative condensers. Other reports of infection have been noted near whirlpools and saunas [32]. It is believed the organism causes up to 4% of all pneumonia cases. Known viral causes of atypical pneumonia include respiratory syncytial virus (RSV), influenza A and B, parainfluenza, adenovirus, severe acute respiratory syndrome (SARS) and measles [33].
