Pneumococcal Pneumonia

Essentials of Diagnosis

Productive cough, fever, rigors, dyspnea, early pleuritic chest pain.

Consolidating lobar pneumonia on chest radiograph.

Gram-positive diplococci on Gram stain of sputum.

General Considerations
The pneumococcus is the most common cause of community-acquired pyogenic bacterial pneumonia. Alcoholism, asthma, HIV infection, sickle cell disease, splenectomy, and hematologic disorders are predisposing factors. The mortality rate remains high in the setting of advanced age, multilobar disease, severe hypoxemia, extrapulmonary complications, and bacteremia.
Clinical Findings
SYMPTOMS AND SIGNS
Presenting symptoms and signs include high fever, productive cough, occasionally hemoptysis, and pleuritic chest pain. Rigors occur within the first few hours of infection but are uncommon thereafter. Bronchial breath sounds are an early sign.
LABORATORY FINDINGS
Pneumococcal pneumonia classically is a lobar pneumonia with radiographic findings of consolidation and occasionally effusion. However, differentiating it from other pneumonias is not possible radiographically or clinically because of significant overlap in presentations. Diagnosis requires isolation of the organism in culture, although the Gram stain appearance of sputum can be suggestive. Sputum and blood cultures, positive in 60% and 25% of cases of pneumococcal pneumonia, respectively, should be obtained prior to initiation of antimicrobial therapy in patients who are admitted to the hospital. A good-quality sputum sample (less than 10 epithelial cells and more than 25 polymorphonuclear leukocytes per high-power field) shows gram-positive diplococci in 80–90% of cases.
Complications
Parapneumonic (sympathetic) effusion is common and may cause recurrence or persistence of fever. These sterile fluid accumulations need no specific therapy. Empyema occurs in 5% or less of cases and is differentiated from sympathetic effusion by the presence of organisms on Gram-stained fluid or positive pleural fluid cultures.
Pneumococcal pericarditis is a rare complication that can cause tamponade. Pneumococcal arthritis also is uncommon. Pneumococcal endocarditis usually involves the aortic valve and often occurs in association with meningitis and pneumonia (sometimes referred to as Austrian’s or Osler’s triad). Early heart failure and multiple embolic events are typical.
Treatment
SPECIFIC MEASURES
Initial antimicrobial therapy for pneumonia is empiric (see Pulmonology for specific recommendations) pending isolation and identification of the causative agent. Once the pneumonia is determined to be caused by Streptococcus pneumoniae, any of several antimicrobial agents may be used depending on the clinical setting, community patterns of penicillin resistance, and susceptibility of the particular isolate. Uncomplicated pneumococcal pneumonia (ie, arterial PO2 > 60 mm Hg, no coexisting medical problems, and single-lobe disease without signs of extrapulmonary infection) caused by penicillin-susceptible strains of pneumococcus may be treated on an outpatient basis with amoxicillin, 750 mg orally twice daily for 7–10 days. For penicillin-allergic patients, alternatives are azithromycin, one 500-mg dose orally on the first day and 250 mg for the next 4 days; clarithromycin, 500 mg orally twice daily for 10 days; doxycycline, 100 mg orally twice daily for 10 days, or levofloxacin, 750 mg orally for 5 days. Patients should be monitored for clinical response (eg, less cough, defervescence within 2–3 days) because pneumococci have become increasingly resistant to penicillin and the second-line agents.
Parenteral therapy is generally recommended for the hospitalized patient at least until there has been clinical improvement. Aqueous penicillin G, 2 million units intravenously every 4 hours, or ceftriaxone, 1 g intravenously every 24 hours, is effective for strains that are not highly penicillin-resistant (ie, strains for which the minimum inhibitory concentration [MIC] of penicillin is > 1 mcg/mL). For serious penicillin allergy or infection caused by a highly penicillin-resistant strain, vancomycin, 1 g intravenously every 12 hours, is effective. Alternatively, a fluoroquinolone (eg, levofloxacin, 500 mg, or a comparable dose of any one of several newer fluoroquinolones now on the market, orally or intravenously) can be used. The total duration of therapy is not well defined, but 10–14 days is standard.
TREATMENT OF COMPLICATIONS
Pleural effusions developing after initiation of antimicrobial therapy usually are sterile, and thoracentesis need not be performed if the patient is otherwise improving. Thoracentesis is indicated for an effusion present prior to initiation of therapy and in the patient who has not responded to antibiotics after 3–4 days. Chest tube drainage may be required if pneumococci are identified by culture or Gram stain, especially if aspiration of the fluid is difficult.
Echocardiography should be done if pericardial effusion is suspected. Patients with pericardial effusion who are responding to therapy and have no signs of tamponade may be monitored and treated with indomethacin, 50 mg orally three times daily, for pain. In patients with increasing effusion, unsatisfactory clinical response, or evidence of tamponade, pericardiocentesis will determine whether the pericardial space is infected. Infected fluid must be drained either percutaneously (by tube placement or needle aspiration), by placement of a pericardial window, or by pericardiectomy. Pericardiectomy eventually may be required to prevent or treat constrictive pericarditis, a common sequela of bacterial pericarditis.
Endocarditis should be treated for 4 weeks with 3–4 million units of penicillin G every 4 hours intravenously; ceftriaxone, 2 g once daily intravenously; or vancomycin, 15 mg/kg every 12 hours intravenously. Mild heart failure may respond to medical therapy, but moderate to severe heart failure is an indication for prosthetic valve implantation, as are systemic emboli or large friable vegetations as determined by echocardiography.
PENICILLIN-RESISTANT PNEUMOCOCCI
The prevalence of penicillin-resistant pneumococci (MIC > 0.1 mcg/mL) in the United States is approximately 20%, although there is considerable regional variability. All blood and cerebrospinal fluid isolates should now be tested for resistance to penicillin. Pneumonia caused by intermediately resistant strains (penicillin MIC > 0.1 mcg/mL but
1 mcg/mL) generally will respond to high-dose penicillin therapy. High-dose penicillin is likely to be effective for infections other than meningitis caused by highly penicillin-resistant strains (MIC > 1 mcg/mL). However, ceftriaxone, 1 g intravenously once daily, or vancomycin, 1 g intravenously every 12 hours, results in a more favorable ratio between serum drug concentration and MIC and may be preferred, especially for immunocompromised patients. An extended-release form of amoxicillin-clavulanate (1000 mg-62.5 mg per tablet) is FDA-approved at a dose of two tablets every 12 hours for 7–10 days for treatment of community-acquired pneumonia, including that caused by penicillin-resistant strains of S pneumoniae with MIC
2 mcg/mL). Fluoroquinolones with enhanced gram-positive activity (eg, levofloxacin 500 mg once daily or moxifloxacin 400 mg once daily) are effective oral alternatives. Penicillin-resistant strains of pneumococci often are resistant to multiple antibiotics, including macrolides, trimethoprim-sulfamethoxazole, and chloramphenicol, and susceptibility must be documented prior to their use.

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