肺炎可据根临床、X线及细菌学发现分类。原发性肺炎发生于既往健康及无肺部病变的人中;继发性肺炎有胸内(如支气管肺癌或支气管扩张)或肺外疾患(如因神经系或上消化道疾患引起的吸入)等潜在原因。继发性肺炎见于抗细菌的防御机制减退、应用免疫抑制剂治疗的白血病或淋巴瘤患者,或较少见的遗传性防御机制缺损者。 Pneumonia according to the root clinical, X-ray and bacteriology found classification. Primary pneumonitis occurs in persons with prior healthy and non-pulmonary disease; secondary pneumonitis has intrathoracic (such as bronchogenic carcinoma or bronchiectasis) or extrapulmonary conditions (such as those caused by neurological or upper gastrointestinal disorders) Other potential causes. Secondary pneumonia is found in the reduction of anti-bacterial defense mechanisms, in patients with leukemia or lymphoma treated with immunosuppressive agents, or in rare cases of hereditary defenses.