Lung infections, also called pneumonia, refer to inflammation of the lung parenchyma. Pulmonary infections are generally classified according to anatomy, etiology and setting of onset: 1. According to anatomy: they can be classified as lobar pneumonia, lobar pneumonia and interstitial pneumonia; 2. According to etiology: they can be classified as bacterial pneumonia, such as Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa and Escherichia coli. Atypical pathogenic pneumonia includes mycoplasma, chlamydia, and legionella. Viral pneumonia includes adenovirus, respiratory syncytial virus, and influenza virus. Pulmonary fungal infections are most commonly Aspergillus, Candida, and Cryptococcus; 3. Classified according to the setting of onset: divided into community-acquired pneumonia and hospital-acquired pneumonia, community-acquired pneumonia is mainly a lung infection, and pathogens are commonly Streptococcus pneumoniae, Mycoplasma, and Chlamydia. Hospital-acquired pneumonia is primarily a hospital-acquired pathogenic infection with common gram-negative bacilli, such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli, with a significantly increased chance of infection. According to the above classification can guide the empirical clinical use of drugs.