AUTHOR AND EDITOR INFORMATION

Section 1 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Ultrasound
• Multimedia
• References

INTRODUCTION

Section 2 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Ultrasound
• Multimedia
• References

Background

Pneumonia is the sixth leading cause of death and the number 1 cause of death from infectious disease in the United States.

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.

Related eMedicine topics:
Pneumonia, Community-Acquired
Pneumonia, Bacterial
Pneumonia, Viral
Pneumonia, Atypical Bacterial

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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.

Clinical Details

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

DIFFERENTIALS

Section 3 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Ultrasound
• Multimedia
• References

Other Problems to be Considered

Hypersensitivity pneumonitis
Vasculitis
Collagen-vascular disease

RADIOGRAPH

Section 4 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Ultrasound
• Multimedia
• References

Findings

When patients present with fever, chills, or cough, pneumonia is suggested on the basis of focal or diffuse opacities.

Controversy exists with regard to the time required for an opacity to appear on chest radiographs. The vast majority of opacities appear within 12 hours. When patients are referred from the community to the radiologist, adequate time has usually lapsed for its detection. However, when nosocomial pneumonia is suspected, these patients may undergo chest radiography within a few hours, when opacities may not yet be visible on radiographs.

In immunosuppressed patients, especially those with coexistent neutropenia, diabetes, alcoholism, or uremia, the appearance of infiltrates may also be delayed.

Other findings that suggest the presence of pneumonia include air bronchograms; the silhouette sign; parapneumonic effusions; and complications of pneumonia, such as lung abscesses, and atelectasis.

Findings that have been associated with an increased mortality, as shown in the multicenter trial by Hasley and colleagues, are bilateral pleural effusion and multilobar pneumonia.

Resolution of radiographic findings

The change in infiltrates on chest radiographs is not necessarily correlated with the activity of clinical disease. In some patients, chest infiltrates may worsen with the start or treatment, despite clinical improvement.

Pneumonia that is slow to resolve after appropriate antibiotic therapy can be a problem. Nonresolving pneumonia has been variously defined by Amberon in 1943, Henden in 1975, and Fein and colleagues in 1987 and 1993. In general, this entity is thought to be present when a patient does not improve clinically or when a radiographic infiltrate resolves slowly despite adequate and appropriate antibiotic therapy. About 10% of diagnostic bronchoscopy procedures and 15% of pulmonary consultations are performed to evaluate a nonresolving infiltrate.

The most common cause of unnecessary invasive evaluation is a failure to appreciate the length of time that infections need to clear radiologically. Studies have shown that impaired host defenses are more important determinants of delayed resolution than the infecting pathogen.

Host factors responsible for delayed resolution of pneumonia include age older than 50 years, smoking; and chronic illnesses, such as diabetes mellitus, renal failure, COPD, and alcoholism.

Bacterial pneumonias usually tend to be unilobar and have cavitary lesions and effusions. Atypical pathogens can cause multilobar involvement with nodular or reticular infiltrates, lobar or segmental collapse, or perihilar adenopathy.

S pneumoniae pneumonia

S pneumoniae causes 10-50% of all cases of CAP. Radiographic consolidation of the alveoli begins in the peripheral airspaces. The disease usually causes a lobar or segmental pattern, and a patchy bronchopneumonic pattern involving the lower lobes is seen in the elderly. A striking characteristic of S pneumoniae infection is its tendency to involve the pleura. Parapneumonic effusions are common in pneumococcal pneumonia.

In patients with bacteremic pneumococcal patients, 50% had clear radiographs at 9 weeks compared with 5 weeks in nonbacteremic pneumococcal pneumonia.

In patients older than 50 years with both alcoholism and COPD, 60% have an abnormal chest radiograph at 14 weeks. In patients younger than 50 years with bacteremia and no underlying illness, 40% have an abnormal chest image at 2 weeks. For the group as a whole, 37% have residual consolidation at 4 weeks, with complete resolution by 18 weeks in almost all patients.

Despite therapy during the initial phase of illness, 52% of bacteremic patients compared with 26% of nonbacteremic patients had radiographs showing deterioration.Jay and colleagues recommended that an appropriate interval for serial radiographic examination is 6 weeks, unless otherwise indicated by a patient's worsening clinical status.

H influenzae pneumonia

H influenzae pneumonia is commonly seen in COPD patients who are smokers; in the elderly; and in those with alcoholism diabetes, sickle cell anemia, or immunocompromise. This organism can be present in up to 38% of outpatients and 10% of hospitalized patients with CAP.

In most patients, radiographs demonstrate a patchy bronchopneumonic pattern, but segmental and lobar consolidation may be seen. Therefore, H influenzae pneumonia is indistinguishable from pneumococcal pneumonia. Pleural effusion is a common finding.Radiographs usually show a multilobar infiltrate and pleural effusions in 50% of cases. Resolution is usually slow.

Klebsiella pneumoniae pneumonia

The radiographic patterns seen in Klebsiella pneumonia include patchy bronchopneumonia and dense lobar consolidations. The alveoli are filled with large amounts of fluid and mucoid suppurative exudates that may cause the volume of the affected lung to increase with bulging of the interlobar fissures, has a rare feature. Although these findings are thought to be characteristic of Klebsiella pneumonia, they may be seen in other causes of pneumonia.

There is a strong tendency for abscess formation as well as pleural involvement. Cavities may develop rapidly after the onset of illness, and these may be associated with massive lung gangrene.

P aeruginosa pneumonia

P aeruginosa pneumonia has a characteristic predilection for the lower lobes. Patchy bronchopneumonia or extensive consolidation may be present. Involvement may be unilateral or bilateral and extensive. Extensive necrosis may be seen, with the formation of parenchymal abscesses. Massive bilateral consolidation is usually associated with a poor prognosis. Nodular infarcts may occur in the lung parenchyma.

S aureus pneumonia

This type of pneumonia may be seen as a complication of influenza, particularly during an epidemic.S aureus pneumonia usually begins in the peripheral airways rather than in the acini proper. In adults, patchy bronchopneumonia is more common and often bilateral, though lobar consolidation may be seen. Late development of abscesses is relatively common. When staphylococcal pneumonia occurs as a complication of influenza, it is usually rapidly progressive with extensive bilateral pneumonia that resembles pulmonary edema.

In children, it is usually a lobar or multilobar consolidation, rapidly progressing with the development of pneumatoceles and/or empyema. The presence of pneumatoceles in children is virtually diagnostic of staphylococcal pneumonia. Rapid progression is seen with lobar or multilobar consolidation. Pneumatoceles may rapidly develop, and empyema is frequent.

Degree of Confidence

In patients with underlying structural lung disease, the appearance of the various signs of pneumonia may not be straightforward.

Narrowing the differential diagnosis of pneumonia into typical and atypical forms on the basis of radiographic appearance alone is not reliable, as shown in a prospective study by Fang et al.

CT SCAN

Section 5 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Ultrasound
• Multimedia
• References

Findings

High-resolution CT findings in CAP

Matsumoto et al sought to clarify the high-resolution CT (HRCT) findings of CAP compared with pathologic findings and to differentiate bacterial and atypical pneumonias. They evaluated 32 patients with CAP, including 18 with bacterial pneumonia and 14 with atypical pneumonia.

Bacterial pneumonia frequently results in airspace consolidation with a segmental distribution in 72%. This finding tended to the middle and outer zones of the lungs. Atypical pneumonia, which included Mycoplasma, Chlamydia, and influenza viral pneumonia, frequently resulted in a centrilobular shadow (64%), an acinar shadow (71%), airspace consolidation, and ground-glass attenuation.

Degree of Confidence

CT scans are increasingly used in clinical practice. Various groups have questioned its usefulness in evaluating pneumonia. Their reports have suggested that its usefulness in the diagnosis of pneumonia is limited to the following settings: (1) to evaluate an indistinct abnormal opacity depicted on a chest radiograph; (2) to assess patchy, ground-glass, or linear/reticular opacities on chest radiographs; (3) to confirm pleural effusion; (4) to examine neutropenic patients with fever of unknown origin (with the use of ultra–thin-section CT).

In clinical practice, co-infection with multiple organisms is not rare.

Underlying abnormalities of the lung parenchymal usually predispose patients to pneumonia. Hence, the overall clinical and radiologic picture must be considered.

ULTRASOUND

Section 6 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Ultrasound
• Multimedia
• References

Findings

In the literature, ultrasonography has been described to help in differentiating consolidation and effusion. Consolidated lung tissue may appear as hypoechoic areas with blurred margins. The texture varies with the amount of aeration, being more heterogeneous with aeration and homogenous with dense consolidation.

Ultrasonography may also help in diagnosing empyema and abscesses.

Degree of Confidence

The role of ultrasonography in clinical practice is limited to the identification and quantification of parapneumonic effusions. This area can then be marked for subsequent diagnostic or therapeutic thoracentesis.

MULTIMEDIA

Section 7 of 8  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Ultrasound
• Multimedia
• References

Media file 1:  Image in a 49-year-old woman with pneumococcal pneumonia. The chest radiograph reveals a left lower lobe opacity with pleural effusion.
	View Full Size Image
Media type:  X-RAY

Media file 2:  Image in a 48-year-old patient with Haemophilus influenzae pneumonia. The chest radiograph shows bilateral opacities with a predominantly peripheral distribution.
	View Full Size Image
Media type:  X-RAY

Media file 3:  Image in a 49-year-old patient with pneumococcal pneumonia. This chest CT shows a left upper lobe opacity extending to the periphery.
	View Full Size Image
Media type:  CT

Media file 4:  Image in a 50-year-old patient with Haemophilus influenzae pneumonia. The chest CT shows a very dense round area of consolidation adjacent to the pleura in the left lower lobe.
	View Full Size Image
Media type:  CT

REFERENCES

Section 8 of 8

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Ultrasound
• Multimedia
• References

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Article Last Updated: Mar 7, 2008