Clinicians define mild pneumonia as patients who are "not too sick," have normal respiratory and mental status, and are able to maintain oral intake. As yet there is no uniform definition of mild pneumonia. By inference, mild pneumonia occurs in younger patients with less comorbidity and has a better outcome than pneumonia that is moderate to severe. "Atypical" pathogens such as Mycoplasma pneumoniae, Chlamydia pneumoniae and respiratory tract viruses are common causes of mild pneumonia.