Pneumonia is a respiratory condition in which there is infection of the lung.Community-acquired pneumonia refers to pneumonia in people who have not recently been in the hospital or another health care facility (nursing home, rehabilitation facility).Pneumonia is a common illness that affects millions of people each year in the United States. Germs called bacteria, viruses, and fungi may cause pneumonia.

肺炎是一种肺部感染的呼吸道疾病。社区获得性肺炎是指院外（包括护理之家、康复中心）人群所得的肺炎。肺炎是一种常见病，在美国，每年有数百万人受感染，其病原菌包括细菌、病毒以及真菌。

Ways you can get pneumonia include:Bacteria and viruses living in your nose, sinuses, or mouth may spread to your lungs.You may breathe some of these germs directly into your lungs.You breathe in (inhale) food, liquids, vomit, or secretions from the mouth into your lungs (aspiration pneumonia)。

罹患肺炎的途径包括：生存于鼻腔、咽腔及口腔的细菌和病毒扩散入肺；患者将致病菌吸入肺部；将口腔中的食物、饮料、呕吐物或者分泌物吸入肺内（吸入性肺炎）。

  Pneumonia caused by bacteria tends to be the most serious. In adults, bacteria are the most common cause of pneumonia.The most common pneumonia-causing germ in adults is Streptococcus pneumoniae (pneumococcus).Atypical pneumonia, often called walking pneumonia, is caused by bacteria such as Legionella pneumophila, Mycoplasma pneumoniae, and Chlamydophila pneumoniae.Pneumocystis jirovecipneumonia is sometimes seen in people whose immune system is impaired (due to AIDS or certain medications that suppress the immune system).Staphylococcus aureus, Moraxella catarrhalis, Streptococcus pyogenes, Neisseria meningitidis, Klebsiella pneumoniae, or Haemophilus influenzae are other bacteria that can cause pneumonia.Tuberculosis can cause pneumonia in some people, especially those with a weak immune system.Viruses are also a common cause of pneumonia, especially in infants and young children.

 细菌引起的肺炎往往是最严重的。在成人肺炎中，细菌是最常见的致病因素。在成人，最常见的肺炎致病微生物是肺炎链球菌；非典型性肺炎，通常称为轻度肺炎，往往由诸如军团菌、肺炎支原体以及肺炎衣原体引起；耶氏肺孢子菌肺炎有时候见于免疫缺陷人群（由艾滋病或者某种免疫系统疾病所致）；化脓性金黄色葡萄球菌、卡它莫拉菌、化脓链球菌、脑膜炎双球菌、肺炎克雷伯氏菌或者流感嗜血杆菌是另一些肺炎致病菌。结核杆菌也可以导致某些人群的肺炎，尤其是免疫力低下人群。病毒也是常见的肺炎因素，尤其是对于婴幼儿。

Risk factors (conditions that increase your chances of getting pneumonia) include:Cerebral palsy；Chronic lung disease (COPD, bronchiectasis, cystic fibrosis)；Cigarette smoking；Difficulty swallowing (due to stroke, dementia, Parkinson's disease, or other neurological conditions)；Immune system problem ；Impaired consciousness (loss of brain function due to dementia, stroke, or other neurologic conditions)；Living in a nursing facility；Other serious illnesses, such as heart disease, liver cirrhosis, or diabetes mellitus（糖尿病）；Recent surgery or trauma；Recent viral respiratory infection (common cold, laryngitis, influenza)。

肺炎易感因素：脑瘫；慢性肺疾病（慢性阻塞性肺病、支气管扩张症、囊性纤维化）；吸烟；吞咽困难（由中风、痴呆、帕金森病或者其他的神经系统疾病所致）；免疫系统疾病；意识障碍（由痴呆、中风或者其他神经系统疾病所致的脑功能障碍）；生活不能自理；其他的严重疾病，比如心脏病、肝硬化或者糖尿病；手术后或者创伤；近期的呼吸道感染（感冒、咽喉炎、流感）。

The most common symptoms of pneumonia are:Cough(with some pneumonias you may cough up greenish or yellow mucus, or even bloody mucus)；Fever, which may be mild or high；Shaking chills；Shortness of breath(may only occur when you climb stairs)。

Additional symptoms include:Confusion, especially in older people；Excessive sweating and clammy skin；Headache；Loss of appetite, low energy, and fatigue；Sharp or stabbing chest pain that gets worse when you breathe deeply or cough。

肺炎的常见症状包括：咳嗽（某些肺炎患者可能会咳黄绿色痰或者血性痰液）；发热，可能是低热也可能是高热；寒战；胸闷气促（可能仅发生于爬楼梯时）。

附加症状包括：意识模糊，尤其是老年人；大汗淋漓、皮肤湿冷；头痛；纳差、乏力、疲劳感；剧烈的或者针刺样胸痛，当深呼吸或者咳嗽的时候还会加剧。

Exams and tests：If you have pneumonia, you may be working hard to breathe, or breathing fast.Crackles are heard when listening to your chest with a stethoscope. Other abnormal breathing sounds may also be heard through the stethoscope or via percussion (tapping on your chest wall).The health care provider will likely order a chest x-ray if pneumonia is suspected.

    Some patients may need other tests, including:Arterial blood gases to see if enough oxygen is getting into your blood from the lungs；CBC to check white blood cell count；CT scan of the chest；Gram's stain and culture of your sputum to look for the organism causing your symptoms. Pleural fluid culture if there is fluid in the space surrounding the lungs.

    辅助检查和实验室检查：如果患者得了肺炎，可能会有呼吸困难或者是呼吸急促；胸部听诊可闻及啰音；异常呼吸音或者异常叩诊音；疑似肺炎患者可给予胸部X线检查。

    某些患者可能需要其他检查，包括：动脉血气分析用于检查血氧含量；白细胞计数；胸部CT扫描；痰液细菌染色与培养以确定致病菌；如果有胸腔积液还可行胸水培养。