Community-acquired pneumonia overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Community-acquired pneumonia is a disease in which individuals who have not recently been hospitalized develop an infection of the lungs. CAP is a common illness and can affect people of all ages. It often causes problems like breathing difficulties, fever, chest pains, and a cough. CAP occurs when the alveoli become filled with fluid and cannot work effectively. It occurs throughout the world and is a leading cause of illness and death. Causes of CAP include bacteria, viruses, fungi, and parasites. CAP can be diagnosed by its symptoms and a physical examination alone, though x-rays, examinations of the sputum, and other tests are often used. CAP is primarily treated with antibiotic medication. Some forms of CAP can be prevented by vaccination.
Historical Perspective
Sir William Osler, known as "the father of modern medicine," appreciated the morbidity and mortality of pneumonia, describing it as the "captain of the men of death" in 1918. However, several key developments in the 1900s improved the outcome for those with pneumonia. With the advent of penicillin and other antibiotics, modern surgical techniques, and intensive care in the twentieth century, mortality from pneumonia dropped precipitously in the developed world. Vaccination of infants against Haemophilus influenzae type b began in 1988 and led to a dramatic decline in cases shortly thereafter.[1] Vaccination against Streptococcus pneumoniae in adults began in 1977 and in children it began in 2000, resulting in a similar decline.[2]
Pathophysiology
Since the lower respiratory tract is maintained sterile by different pulmonary defence mechanisms,[3] acquiring community-acquired pneumonia connotes a breach of host defence mechanisms and/or overwhelming inoculation of virulent infectious agents. Modes of transmission include macro- or micro-aspiration, from circulation, local spead, traumatic inoculation, or can be iatrogenic. Impaired immunity and inability to filter out pathogen increase the risk for developing pneumonia. Causative etiologies vary with age, immune status, geographical area, and comorbid conditions.
Causes
Community-acquired pneumonia can be caused by viral, bacterial, and fungal organisms. Causative etiology varies with age, immune status, epidemiologic background, and comorbidity.
Differentiating Community-acquired pneumonia from other Diseases
Pneumonia should be differentiated from other conditions that cause cough, fever, shortness of breath and tachypnea, such as asthma, COPD, CHF, cancer, GERD, and pulmonary emboli.
Epidemiology and Demographics
Pneumonia is the leading cause of death in children younger than 5 years of age worldwide. Both children and the elderly are at a higher risk for pneumonia complications. Countries in the Middle East and Africa have a higher mortality rate among children with pneumonia.
Risk Factors
The risk factors for pneumonia include: smoking, age, immunosuppression, exposure to chemicals, underlying lung disease, and exposure to chemicals.
Natural History, Complications and Prognosis
Complications including sepsis, respiratory failure, pleural effusion, and empyema may occur despite appropriate antibiotic treatment. Complications are associated with bacterial pneumonia more frequently than viral pneumonia. Most types of bacterial pneumonia can be cured within one to two weeks with the appropriate medication. Viral pneumonia may last longer, and mycoplasmal pneumonia may take four to six weeks to resolve completely. The eventual outcome of an episode of pneumonia depends on how ill the person is when he or she is first diagnosed.
Diagnosis
CURB-65
CURB-65 is a clinical prediction rule that has been validated for predicting mortality in community-acquired pneumonia[4] and infection of any site[5]. The CURB-65 is based on the earlier CURB score[6] and is recommended by the British Thoracic Society for the assessment of severity of pneumonia.[7]
Pneumonia Severity Index
The pneumonia severity index is a clinical prediction rule that medical practitioners can use to calculate the probability of morbidity and mortality among patients with community acquired pneumonia.[8]
History and Symptoms
Common symptoms of pneumonia include cough, fever, and difficulty breathing. Patients with CAP usually present with the history of having a close contact with similar symptoms.
Physical Examination
Physical examination by a health care provider may reveal fever or sometimes low body temperature, an increased respiratory rate, low blood pressure, a fast heart rate, or a low oxygen saturation, which is the amount of oxygen in the blood as indicated by either pulse oximetry or blood gas analysis. People who are struggling to breathe, who are confused, or who have cyanosis (blue-tinged skin) require immediate attention. A lack of normal breath sounds, the presence of crackling sounds (rales), or increased loudness of whispered speech (whispered pectoriloquy) can identify areas of the lung that are stiff and full of fluid, called "consolidation." The examiner may also feel the way the chest expands (palpation) and tap the chest wall (percussion) to further localize consolidation. The examiner may also palpate for increased vibration of the chest when speaking (tactile fremitus).[9]
Laboratory Findings
Laboratory findings such as leukocytosis are helpful for the diagnosis of bacterial pneumonia or to assess the status of the patient. Sputum samples need to be collected from every patient and gram staining and culture need to be performed to determine the exact pathogen causing the pneumonia. Other tests include urine antigen test, PCR, C-reactive protein and procalcitonin.
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Treatment
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Primary Prevention
Cost-Effectiveness of Therapy
Future or Investigational Therapies
References
- ↑ Adams WG, Deaver KA, Cochi SL, et al. Decline of childhood Haemophilus influenzae type b (Hib) disease in the Hib vaccine era.JAMA1993;269:221-6. PMID 8417239
- ↑ Whitney CG, Farley MM, Hadler J, et al. Decline in invasive pneumococcal disease after the introduction of pneumococcal protein-polysaccharide conjugate vaccine. New Engl J Med. 2003;348:1737–1746. PMID 12724479
- ↑ Mason, CM.; Nelson, S. (2005). "Pulmonary host defenses and factors predisposing to lung infection". Clin Chest Med. 26 (1): 11–7. doi:10.1016/j.ccm.2004.10.018. PMID 15802161. Unknown parameter
|month=ignored (help) - ↑ Lim WS, van der Eerden MM, Laing R; et al. (2003). "Defining community acquired pneumonia severity on presentation to hospital: an international derivation and validation study". Thorax. 58 (5): 377–82. PMID 12728155.
- ↑ Howell MD, Donnino MW, Talmor D, Clardy P, Ngo L, Shapiro NI (2007). "Performance of severity of illness scoring systems in emergency department patients with infection". Academic emergency medicine : official journal of the Society for Academic Emergency Medicine. 14 (8): 709–14. doi:10.1197/j.aem.2007.02.036. PMID 17576773.
- ↑ Lim WS, Macfarlane JT, Boswell TC; et al. (2001). "Study of community acquired pneumonia aetiology (SCAPA) in adults admitted to hospital: implications for management guidelines". Thorax. 56 (4): 296–301. PMID 11254821.
- ↑ "BTS Guidelines for the Management of Community Acquired Pneumonia in Adults". Thorax. 56 Suppl 4: IV1–64. 2001. PMID 11713364.
- ↑ Fine MJ, Auble TE, Yealy DM, Hanusa BH, Weissfeld LA, Singer DE, Coley CM, Marrie TJ, Kapoor WN. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med. 1997 Jan 23;336(4):243–250. PMID 8995086
- ↑ Metlay JP, Kapoor WN, Fine MJ. Does this patient have community-acquired pneumonia? Diagnosing pneumonia by history and physical examination. JAMA 1997; 278:1440. PMID 9356004