Pneumonia and bronchitis are not contagious. Although they are infectious diseases, they are not infectious diseases and do not meet the characteristics of infectious diseases, i.e., there is no fixed source of infection, an appropriate route of transmission, and a specific susceptible population. Pneumonia refers to an acute inflammation of the lung tissue, mostly caused by bacterial infection. Bronchitis refers to acute and chronic inflammation of bronchial and submucosal bronchial tissues, caused by both viral and bacterial infections. Common viruses and bacteria are not contagious or have very low infectivity, are excreted through the patient’s saliva or sputum, but are limited in number and activity, drift in the air and are blocked by mechanical barriers in the upper respiratory tract, such as the nasal cavity, and rarely enter the lower respiratory tract to cause disease. Therefore, pneumonia and bronchitis are not contagious.