The different causative agents of lung infections, clinical infectiousness is also different. Common causative agents include bacteria, viruses and atypical pathogens. Clinically, viral pneumonia and mycoplasma pneumonia are infectious, and proper isolation should be carried out after diagnosis, especially in the elderly as well as children, and active treatment should be made. Patients with viral pneumonia need to use antiviral drugs, such as oseltamivir and abidol. Mycoplasma pneumonia requires the use of antibiotics, macrolides or quinolones, such as azithromycin, erythromycin, levofloxacin, moxifloxacin and so on. After treatment, the patient’s infectiousness will gradually decrease until it disappears. Treating the cause is a very important way to reduce infectiousness.