Community‐Acquired Pneumonia

Chapter 13 Community-Acquired Pneumonia



Key Points



1 Aspiration pneumonia accounts for up to 15% of community-acquired pneumonia (CAP) cases, and refers to a lung infection caused by inhalation of oropharyngeal secretions colonized with pathogenic bacteria. If unwitnessed, the diagnosis is inferred when an at-risk patient (nursing home resident, stroke patient) presents with an infiltrate in a characteristic pulmonary location.

2 Aspiration pneumonitis refers to chemical injury to lung caused by inhalation of sterile gastric contents and occurs in patients with altered consciousness.

3 Patients with CAP may present with fever, cough, sputum production, dyspnea, pleurisy, and extrapulmonary symptoms. Chest x-ray usually differentiates CAP from bronchitis and upper respiratory tract infections.

4 On physical examination, the patient may have fever, tachypnea, respiratory distress, hypoxemia, pulmonary crackles, and bronchial breath sounds.

5 Prognostic scoring rules may be used in conjunction with clinical judgment to determine whether a patient with CAP should be hospitalized.

6 Initial testing for patients with CAP requiring hospitalization should include a complete blood count and differential, chemistry panel with renal function and glucose, assessment of arterial oxygenation, and PA and lateral chest x-ray.

7 Collecting blood and sputum samples in every patient with CAP is controversial, because there is no clear benefit to establishing the causative agent in CAP.

8 The most common CAP pathogens are Streptococcus pneumoniae, Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella species.

9 Presenting features of CAP do not predict the causative agent.

10 Approximately 20% of S. pneumoniae are penicillin-resistant and one third are macrolide-resistant. Fluoroquinolone resistance is low in the United States.

11 Infectious Diseases Society of America recommends a beta-lactam plus a macrolide or fluoroquinolone monotherapy as empiric treatment for patients with CAP admitted to the general medical ward.

12 Patients admitted to the intensive care unit should receive coverage for S. pneumoniae, Legionella, and possibly Pseudomonas.

13 The optimum duration of antibiotic administration is unknown (7–10 days is reasonable in most cases).

14 Even with appropriate antibiotic use, fevers may take up to 72 hours to fully resolve. Persistent fevers or declining clinical status should prompt an evaluation for complications or worsening pneumonia.

15 Pulmonary infiltrates can take weeks or months to fully resolve following treatment.

16 Aspiration pneumonitis does not usually require antibiotic therapy unless the patient is at risk for bacterial colonization of the gastric contents or the symptoms do not resolve within 48 hours of the event.

17 Therapy for aspiration pneumonia includes a swallowing evaluation and antibiotics with activity against gram-negative bacteria. Anaerobic coverage is appropriate in some settings (e.g., a lung abscess or severe periodontal disease).

18 Preventive measures against CAP include smoking cessation and administration of the polysaccharide pneumococcal and inactivated influenza vaccines.



Definitions


Nosocomial pneumonia: Hospital-acquired pneumonia starting at least 48 to 72 hours after admission.


Aspiration pneumonia: Lung infection caused by inhalation of oropharyngeal secretions that are colonized with pathogenic bacteria.


Aspiration pneumonitis: Chemical injury to lung caused by inhalation of sterile gastric contents.



Epidemiology


An estimated 4 million cases of community-acquired pneumonia (CAP) occur annually in the United States, accounting for at least 600,000 hospital admissions. CAP is the sixth leading cause of death. The mortality rate for hospitalized CAP patients is approximately 1 in 10 but this rate is higher in specific populations (e.g., nursing home residents) and approaches 40% in the severely ill who require admission to the intensive care unit.



Aspiration Pneumonia


Aspiration pneumonia accounts for up to 15% of CAP cases and is common among nursing home residents. The risk of aspiration pneumonia is higher in the elderly and patients with dysphagia, stroke, or critical illness and lower in patients without teeth. Usually, the episode of aspiration is not witnessed; the diagnosis is inferred when patients at risk for aspiration present with an infiltrate in a characteristic pulmonary location (posterior upper lobe or apical lower lobe segments from recumbent aspiration, and basal lower lobe segments from upright or semi-recumbent aspiration). Patients with aspiration pneumonia have clinical features similar to those of patients with CAP but have a higher incidence of pulmonary cavitation and abscess formation.


Early studies identified anaerobic organisms as the predominant pathogens in patients with aspiration pneumonia, but this has not been confirmed in recent studies.



Aspiration Pneumonitis


Aspiration pneumonitis occurs in patients with altered consciousness (e.g., seizures, drug overdose, and anesthesia). The aspirated gastric contents are usually sterile but the acidity burns the lung, causing an intense inflammatory reaction. Bacterial infection may subsequently develop, but the prevalence of this complication is unknown. Infection likely plays some role if the gastric contents are colonized with pathogenic organisms (e.g., gastroparesis, enteral feedings, and ant-acid therapy raise the gastric pH and increase the risk of bacterial colonization).


Aspiration pneumonitis has a broad spectrum of presentation, ranging from cough or wheeze to cyanosis, shortness of breath, hypoxemia, hypotension, acute respiratory distress syndrome, and death.



Causes of Community-Acquired Pneumonia


Most cases of CAP are limited to a few key organisms (Box 13-1), although in most cases the cause of the pneumonia is not identified. S. pneumoniae (pneumococcus) accounts for approximately two thirds of all cases of bacteremic pneumonia. Other common pathogens include M. pneumoniae, C. pneumoniae, and Legionella species, which have been reported to cause “atypical” pneumonia (pneumonia that does not present with classic signs and symptoms). In the past, the presenting signs and symptoms of pneumonia were thought to predict the causative agent, but we now know this to be untrue—there is a wide spectrum of presentation for each organism that is known to cause CAP, and these pathogens cannot be distinguished based only on symptoms, clinical signs, and findings on chest x-ray.



Symptoms and Signs


Immunocompetent adults presenting with pneumonia may have fever (∼ 80%), cough (> 90%), sputum production (∼ 66%), dyspnea (∼ 66%), and pleuritic chest pain (∼ 50%). However, these symptoms may also occur in patients with bronchitis or upper respiratory tract infections. Therefore, symptoms at presentation do not reliably distinguish between CAP and other respiratory illnesses. Bronchitis and upper respiratory tract infections are usually caused by viruses and can almost always be differentiated from pneumonia using chest x-ray. One caveat is that the chest x-ray may be normal in patients with CAP who are dehydrated. In this setting, the infiltrate should become visible following adequate hydration.


Extrapulmonary symptoms, including gastrointestinal symptoms, headache, myalgias, and arthralgias, occur in up to one third of CAP patients.


Physical exam findings depend on the severity of the infection. The patient may have fever, tachypnea, hypoxemia, pulmonary crackles, bronchial breath sounds, and respiratory distress with accessory respiratory muscle use.



Laboratory Data


Initial laboratory testing for patients with CAP requiring hospital admission should include:


1 Complete blood count (with differential) and chemistry panel, including assessment of renal function and glucose

2 Blood cultures (controversial; see following text)

3 PA and lateral chest x-ray, which may show a lobar (occurring in one lobe of the lung) or segmental pulmonary infiltrate, patchy or diffuse lung infiltrates, or pleural effusion. The “air bronchogram sign” occurs when dense lung consolidation delineates air in the intrapulmonary bronchi, which are not normally visualized on chest x-ray. This sign confirms the presence of lung consolidation. The chest x-ray is also useful for ruling out complications, such as pneumothorax, abscesses, and empyema.

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Mar 25, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Community‐Acquired Pneumonia

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