所患肺炎的病原除了常见病原外，还可有一些少见病原感染，如弓形虫、卡氏肺孢子虫、真菌、G<sup>-</sup>肠道细菌、厌氧菌、努卡菌、军团菌及病毒（单纯疱疹病毒、巨细胞病毒和水痘带状疱疹病毒）。
O O B-dis I-dis O O O O O O O O O O O O O O O O O O O O O O O O B-mic I-mic I-mic O B-mic I-mic I-mic I-mic I-mic I-mic O B-mic I-mic O B-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic O B-mic I-mic I-mic O B-mic I-mic I-mic O B-mic I-mic I-mic O B-mic I-mic O O O B-mic I-mic I-mic I-mic O B-mic I-mic I-mic I-mic I-mic O B-mic I-mic I-mic I-mic I-mic I-mic I-mic I-mic O O