Pneumonia is an acute infectious disease of the respiratory tract that occurs in the alveoli. Its symptoms are mainly fever and malaise with cough and sputum, and the main diagnosis is based on the finding of large solid lesions and exudates in the lung lobes on chest radiographs or CT. Pneumonia is classified as bacterial pneumonia, viral pneumonia or mycoplasma pneumonia depending on the pathogen. There are also other causes of pneumonia that are not infectious, including allergic pneumonia is also present. The prognosis for most pneumonia is relatively good, and the most common bacterial pneumonia, such as Streptococcus pneumoniae pneumonia, can be cured in almost 90% or more of cases. Generally its infectiousness varies depending on the pathogen. In general, pneumonia is not very contagious because the pathogens that cause pneumonia are often found in the environment. These pathogens do not cause disease in humans when the resistance is normal, but only when the resistance is drastically reduced, such as by cold, rain, or drunkenness, and the pathogens that live in the human oropharynx or in the environment will develop and cause acute inflammation. A normal person who comes in contact with a pneumonia patient will not usually develop the disease because the pathogens that caused the pneumonia patient were originally present in him, so it is not highly contagious. However, some specific pneumonia, such as SARS virus and influenza virus, which cause pneumonia, are more contagious because these pathogens are extremely infectious, so the contagiousness of pneumonia depends on the pathogen. Some pathogens cause pneumonia, such as viral pneumonia, especially some highly contagious viruses, such as SARS virus caused by viral pneumonia, including some rare influenza virus pneumonia, the prognosis is relatively poor, the patient is prone to acute respiratory failure, or even death.