Lung infections can be divided into community-acquired pneumonia and hospital-acquired pneumonia depending on the location of the infection, and the symptoms of each are described below. Some patients with community-acquired pneumonia have symptoms of upper respiratory tract viral infections before the onset of the disease. The common symptoms are cough and sputum, which can be dry, with mucous or purulent sputum, sometimes rusty or bloody sputum, or even hemoptysis; with lung abscess, large amounts of foul-smelling sputum can occur; shortness of breath and chest pain can also occur. The systemic manifestations of pneumonia include fever, chills, headache, malaise, nausea, vomiting, abdominal pain, diarrhea, myalgia and arthralgia. Pulmonary infections caused by specific pathogens such as Legionella pneumophila can exhibit characteristic systemic symptoms such as hyponatremia, relatively slow pulse, renal involvement, and psychiatric abnormalities, but this is uncommon. Hospital-acquired pneumonia has an insidious onset, and fever and respiratory symptoms are often not typical. Patients treated with mechanical ventilation may present only with increased cyanosis and increased resistance of the airway. The symptoms of pulmonary infections are greatly influenced by the location of infection, the causative agent and the underlying disease, and the prognosis varies with the above conditions.