Introduction
Background
Pneumonia is the sixth leading cause of death and the number 1 cause of death from infectious disease in the United States.1,2,3,4,5,6,7
Community-acquired pneumonia
Community-acquired pneumonia (CAP) affects approximately 5.6 million adults in the United States annually, resulting in approximately 1.1 million hospital admissions.
The estimated average cost of inpatient care for CAP is $7500, compared with $150-$350 for outpatient care. Therefore, the initial site-of-care decision is perhaps the most important decision the physician makes in terms of the cost of treating this illness. Studies have shown that physician overestimate the risk of death, leading to unnecessary admissions. In others studies, physicians failed to recognize the severity of illness. These problems have led to the development of various prediction rules.
British Thoracic Society and Pneumonia Patient Outcomes Research Team
The British Thoracic Society (BTS) and the Pneumonia Patient Outcomes Research Team (PORT) are complimentary. The BTS rule is focused on identifying high-risk patients so that their severity of illness is not underestimated, whereas the PORT approach is focused on recognizing some patients as low risk so that severity of illness is not overestimated. It is important to understand that these prediction rules have their limitations and are not substitutes for good clinical judgment.
Typical versus atypical syndromes
The classification into these 2 groups arose from the observation that the presentation and natural history of some patients with pneumonia were different compared with those with pneumococcal infection.
Pathogens like Haemophilus influenzae, Staphylococcus aureus, and gram-negative enteric bacteria cause clinical syndromes similar to that due to Streptococcus pneumoniae. However, other pathogens cause an atypical pneumonia syndrome, and this was initially attributed to Mycoplasma pneumoniae.
Other pathogens, including bacteria and viruses are now known to cause similar syndromes indistinguishable from that due to M pneumonia. Therefore, the term atypical pneumonia represents diverse etiologic entities and may have limited clinical value.
Pathophysiology
Most pathogens responsible for CAP reach the lungs after first colonizing the oropharynx. Community respiratory pathogens that enter via inhalation without preceding colonization of the oropharynx include Mycobacterium tuberculosis, Legionella species, and certain viruses.
If the process has extended to the pleural space, associated empyema may be present.
Mortality/Morbidity
The overall mortality rate is approximately 14%, ranging from 5% in studies including both ambulatory and hospitalized patients to 14% in hospitalized patients. Rates are as high as 40% in ICU patients. The mortality rate is increased in the elderly (18%) and in nursing home patients (30%).
Sex
Typical bacterial pneumonia is more common in men than in women.
Age
The incidence is increased in the elderly as a result of associated comorbidities, reduced immunocompetence, and an increased risk of aspiration.
Presentation
Pathogens
The pathogens causing CAP vary in relation to specific risk factors. The simplest approach is to group patients on the basis of the physician's decision to treat them as outpatients or inpatients.
In all groups, the most common pathogen is still a pneumococcal species, which must be adequately treated. In severe CAP, pneumococcal species are still the most common organisms, though some investigators have found Legionella species, H influenzae, and gram-negative organisms to be important pathogens.
In young, healthy persons, atypical pathogens and viruses, particularly H influenzae, are of concern in cigarette smokers with or without chronic obstructive pulmonary disease (COPD).
In the elderly and in chronically ill persons, H influenzae and enteric gram-negative bacteria are common organisms.
Anaerobes should be considered in those at risk for aspiration, eg, those with poor oral hygiene, altered swallowing reflexes, or impaired consciousness.
Pseudomonas aeruginosa is identified from the respiratory tract cultures in 5-15% of all patients with severe CAP.
Modifying factors
Modifying factors are clinical conditions that put patients at risk for infections with specific pathogens. Certain modifying factors increase the risk of infection with specific pathogens, as follows:
- Penicillin- and drug-resistant pneumococcal bacteria
- Age older than 65 years
- Beta-lactam therapy within 3 months
- Alcoholism
- Immunosuppressive illness
- Multiple medical comorbidities
- Exposure to a child in a day care center
- Enteric gram-negative organisms
- Residence in a nursing home
- Underlying cardiopulmonary disease
- Multiple medical comorbidities
- Recent antibiotic therapy
- P aeruginosa
- Structural lung disease (eg, bronchiectasis)
- Corticosteroid therapy (>10 mg/d prednisone)
- Broad-spectrum antibiotic therapy for more than 7 days in the past month
- Malnutrition
Prevention of CAP
Vaccination against influenza and pneumococcal infection is the mainstay in preventing pneumonia in older patients. All persons older than 50 years who are at risk for influenza complications and household contacts of high-risk persons should receive inactivated influenza vaccine, as advised by the Advisory Committee on Immunization Practices (ACIP).
The optimal time for influenza vaccination is in October and November. Vaccination in December is recommended for those who have not been vaccinated earlier.
The injected vaccination is the preferred formulation for most persons at risk. The intranasally administered live attenuated vaccine is an alternative formulation for some persons aged 5-49 years without chronic underlying diseases, immunodeficiency, asthma, or other chronic medical conditions.
The pneumococcal vaccine is recommended for use according to current ACIP guidelines for patients older than 65 years with selected high-risk concurrent disease. The overall effectiveness against invasive pneumococcal disease among immunocompetent patients aged 65 years or older is 75%, with the efficacy decreasing with advancing age. Older adults may also benefit from the vaccination of children against pneumococcal disease because of decreased pneumococcal transmission.
Influenza and pneumococcal vaccination can be administered at the same time in different arms. The vaccines should be provided at the of a patient's discharge from the hospital or at the conclusion of outpatient treatment. Standing orders might help to ensure that patients are vaccinated.
Preferred Examination
The preferred examinations for evaluating typical bacterial pneumonia are the following:
- Chest radiography with posteroanterior and lateral views
- Sputum Gram staining and culturing
- Assessment of oxygenation with pulse oximetry or determination of arterial blood gasses
- Complete blood cell count and differential
- Blood chemistry tests including tests for electrolytes and renal and liver function
- Two sets of blood cultures prior to starting antibiotics
- Sampling of substantial pleural effusion
- Transtracheal aspiration, with bronchoscopy as indicated
- Serologic studies and cold agglutinin tests if indicated for epidemiologic studies
Differential Diagnoses
Other Problems to Be Considered
Hypersensitivity pneumonitis
Vasculitis
Collagen-vascular disease
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Further Reading
Keywords
typical pneumonia, community-acquired pneumonia, CAP, red hepatization, gray hepatization
