First of all, community-acquired pneumonia is contagious because it is called out-of-hospital pneumonia referring to the existence of a certain incubation period for infection in the community, due to the wide variety of community-acquired pneumonia pathogens, including bacteria, viruses, and atypical pathogens. The results of the survey show that Streptococcus pneumoniae is still the common pathogen of community-acquired pneumonia, and Haemophilus influenzae is also more common, while Chlamydia pneumoniae, Mycoplasma, Legionella, and atypical pathogens are increasing year by year, and all of them are significantly infectious after infection for the above pathogens, some of which can cause small outbreaks. The composition of the current community-acquired pneumonia pathogens in adults in China is divided into two main features. The first is that the infection rate of Mycoplasma pneumoniae has exceeded that of Streptococcus pneumoniae infection, becoming the primary pathogen of community-acquired pneumonia in adults in China.