Pneumonia is an inflammation of the lungs. The term is almost always used to refer specifically to infections of the lungs caused by bacteria, viruses, fungi or other parasites; however, it can also refer to lung injury caused by physical or chemical irritants, in which case the term pneumonitis is used to differentiate the condition from infectious pneumonia. This article uses pneumonia only in the first sense, that of infection. Pneumonia may occur in people of all ages, although young children, the elderly, and immunocompromised patients are especially at risk. Antimicrobial drugs are often used to treat pneumonia.
Symptoms of pneumonia commonly include shortness of breath; coughing that produces greenish or yellow sputum; a high fever (that may be accompanied with sweating, chills, and rigors [shaking]); sharp or stabbing chest pain, worsened by deep breaths or coughs (pleuritic chest pain); and rapid, shallow breathing that is often painful. Less commonly, there may be hemoptysis (the coughing up of blood), headaches (including migraine headaches), excessive sweating and clammy skin, loss of appetite, excessive fatigue, cyanosis (a blueness of the skin), nausea, vomiting, diarrhea, and arthalgia (joint pain) or myalgia (muscle aches). The manifestations of pneumonia, like those for many conditions, may not be typical in older people. They may instead experience new or worsening confusion, or falls.
Signs of pneumonia are tachypnea (rapid breathing), dullness to percussion, egophony, crackles, tachycardia (rapid heart rate), and fever.
There are several different classification schemes: microbiological, radiological, age-related, anatomical, point of acquiring infection. The main classification used in medical journals is that between the point of infection: community-acquired and hospital-acquired. Community-acquired pneumonias are pneumonias in a patient who is not or has not recently been hospitalized, whereas hospital-acquired pneumonias (or nosocomial pneumonias) are found in hospitalized or recently discharged patients. Furthermore, infections in the immunocompromised, as well as aspiration pneumonia, are usually treated as separate disease entities as they have other causal agents, as well as a different clinical course.
Aside from these, there are several other terms used to classify pneumonias. A lobar pneumonia is an infection that involves, and is limited to, a single lobe of a lung (generally due to Streptococcus pneumoniae). In contrast, multilobar pneumonia involves more than one lobe. Ventilator-associated pneumonia can be considered a subset of hospital-acquired pneumonia; it occurs following intubation and mechanical ventilation for at least 48 hours. "Walking pneumonia" is an outdated term for pneumonia in a patient who is still able to walk—that is, a mild pneumonia, usually due to Mycoplasma. Pneumococcal pneumonia is due to S. pneumoniae (around half of all pneumonias). Finally, atypical pneumonia is due to either Mycoplasma, Chlamydia, or Legionella.
Common Respiratory Tract Infections
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