（四）根据患儿感染来源1.社区获得性肺炎（communityacquiredpneumonia，CAP）是指无明显免疫抑制的患儿在医院外或住院48小时内发生的肺炎，病毒、细菌、支原体、衣原体是CAP的主要病原；病毒感染在肺炎初始阶段居重要地位；仅10%～15%由细菌引起，而且以肺炎链球菌、流感嗜血杆菌、卡他莫拉菌和甲氧西林敏感的金黄色葡萄球菌为主；在5岁以上的儿童肺炎支原体和肺炎衣原体感染明显增加。
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