Whether severe pneumonia is contagious depends not on the severity of the pneumonia, but on whether the causative organism or virus that causes severe pneumonia, is infectious. If the causative organism or virus is infectious, it can produce contagion, such as infection with Mycobacterium tuberculosis, Mycobacterium diphtheriae, Mycobacterium pertussis, or severe pneumonia caused by infection with the New Coronavirus or SARS virus, which is infectious. Some atypical pathogenic bacteria, such as Chlamydia, Mycoplasma, katamora, Haemophilus influenzae, and Legionella, can be transmitted by droplets, but they are not infectious because they are not very contagious. If the causative bacteria or viruses are not infectious, they generally do not produce contagion, such as severe pneumonia caused by pathogenic infections of Streptococcus pneumoniae, Staphylococcus aureus, Klebsiella pneumoniae, Haemophilus influenzae, and Pseudomonas aeruginosa. In addition, severe pneumonia due to non-infectious viral infections are not infectious, such as metapneumovirus. During treatment, it is necessary to presume and determine the type of pathogenic bacteria based on laboratory test results, as well as the patient’s age, signs, concomitant symptoms, and chest x-ray, and to take the appropriate antibiotic treatment, and to retain pathogenic samples for testing before administering the medication. In addition, severe pneumonia often causes other organ dysfunction and even hemodynamic instability and shock, so patients should be closely monitored for vital signs, cardiopulmonary function and nutritional support to maintain hemodynamic stability.