The Ministry of Health defines pneumonia of unknown origin as pneumonia of unknown origin, which is contagious and can be diagnosed from the following four aspects: 1. the patient presents with symptoms of fever. 2. the symptoms do not improve significantly after about 5 days of treatment with anti-infective and antiviral drugs. 3. the patient’s symptom profile is similar to that of common pneumonia or acute respiratory distress syndrome, and also similar to that of SARS virus infection and human avian flu virus infection. 4. Patients with reduced white blood cell count or lowered lymphocyte classification count are seen in routine blood tests done early in the course of the illness. Unexplained pneumonia is generally more severe and the morbidity and mortality rate is higher than that of general pneumonia.