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Pneumonia, bacterial

Description of Medical Condition

An acute, bacterial infection of the lung parenchyma. Infection may be community-acquired or nosocomial (hospital acquired by an inpatient for at least 48 hours or inpatient in the previous 90 days). Most commonly, community-acquired disease is caused by Streptococcus pneumoniae or Mycoplasma pneumoniae. Hospital-acquired pneumonia is usually due to gram negative rods (60%, such as Pseudomonas) or Staphylococcus (30%).

Pneumonia, bacterial

System(s) affected: Pulmonary

Genetics: No known genetic pattern

Incidence/Prevalence in USA:

  • Incidence-community-acquired: 1200 cases/100,000 population per year
  • Incidence — nosocomial: 800 cases/100,000 admissions per year

Predominant age: Age extremes

Predominant sex: Male > Female

Medical Symptoms and Signs of Disease

  • Cardinal signs and symptoms
    • Cough and fever
    • Chest pain (pleuritic)
    • Chill, with sudden onset
    • Dark, thick or bloody (rusty) sputum
  • Respiratory
    • Signs of consolidation
    • Rales
    • Egophony
    • Signs of pleural involvement
    • Decreased breath sounds
    • Dullness to percussion
    • Friction rub
  • Signs of respiratory distress
    • Tachypnea/tachycardia (or bradycardia)
    • Cyanosis
  • Central nervous system
    • Mentation changes to include anxiety, confusion and restlessness
  • Gastrointestinal
    • Abdominal pain
    • Anorexia

What Causes Disease?

  • Sources
    • Aspiration from the oropharynx
    • Inhalation
    • Hematogenous spread
  • Bacterial pathogens
    • Streptococcus pneumoniae (pneumococcus)
    • Haemophilus influenzae
    • Mycoplasma pneumoniae
    • Staphylococcus aureus
    • Legionella pneumophila
    • Chlamydia pneumoniae, C. psittaci
  • Moraxella catarrhalis (Branhamella catarrhalis)
    • Pseudomonas aeruginosa
    • Klebsiella pneumoniae (and other gram-negative rods)
    • Anaerobes

Risk Factors

  • Tobacco smoking
  • Recent/concurrent viral infections
  • Hospitalization to include mechanical ventilation, antecedent antibiotics, NG tubes
  • Age extremes
  • Alcoholism
  • AIDS or other immunosuppression
  • Renal failure
  • Cardiovascular disease
  • Functional asplenia
  • Chronic obstructive pulmonary disease
  • Diabetes mellitus
  • Malnutrition
  • Malignancy
  • Altered level of consciousness or gag (e.g., seizures, stroke, neuromuscular disease, etc.)
  • Occupational exposure
  • Poorly implemented infection control practices (poor handwashing)
  • Postoperative atelectasis

Pneumonia, bacterial

Diagnosis of Disease

Differential Diagnosis

Other causes of infectious pneumonitis: Viruses (human metapneumovirus, SARS coronavirus, respiratory syncytial, adenovirus, CMV, parainfluenza, influenzae A and B, varicella, measles, rubella, hantavirus); Nocardia; Fungi (Blastomyces, Cryptococcus, Aspergillus, Histoplasma, Coccidioides, Pneumocystiscarinii); Protozoans (Toxoplasma); Rickettsia (Coxiella burnetii — Q fever). Also tuberculosis, pulmonary embolism with infarction, bronchiolitis obliterans with organizing pneumonia (BOOP), pulmonary contusion, pulmonary vasculitis, acute sarcoid, hypersensitivity pneumonitis, ARDS, pneumothorax, and other causes.


  • CBC — leukocytosis with an immature shift on differential; ESR, CRP
  • Chem — hyponatremia (SIADH)
  • ABG — hypoxemia
  • ABG — hypocapnia initially, then hypercapnia
  • Blood culture — positive in 10-20% of adult patients and 7% of pediatric patients with community-acquired pneumonia (partially because many have been pre-treated with antibiotics), 8-20% nosocomial pneumonia

Drugs that may alter lab results: Antecedent antibiotics

Disorders that may alter lab results: Refer to lab test reference

Pathological Findings

  • Lung:
    • Segmental, lobar, or multifocal peribronchial consolidation
    • Positive gram stain for bacteria

Special Tests

  • Decubitus CXR to investigate for empyema or parapneumonic effusion
  • Gram stain and culture of pleural fluid
  • pH of pleural fluid (iced, airless sample sent to blood gas laboratory)
  • Urine legionella antigen (in ICU/severe cases
  • Tuberculin skin test (PPD) — for hilar adenopathy or upper lobe involvement


  • CXR (with lateral decubitus views if pleural effusion present)
    • Lobar or segmental consolidation (air bronchogram)
    • Bronchopneumonia
  • Interstitial infiltrate
    • Pleural effusion (free-flowing or loculated)
  • Ultrasound recommended to check for location and presence of loculations before thoracentesis

Diagnostic Procedures

  • Gram stain and culture of sputum (induced, if necessary)
  • Nasotracheal suctioning for culture
  • Transtracheal aspirate for culture
  • Bronchoscopy with bronchoalveolar lavage or protected telescoping catheter brushing for culture
  • Thoracentesis for pleural fluid studies
  • Blood culture, especially if hospitalized — prior to antibiotics

Treatment (Medical Therapy)

Appropriate Health Care

  • Community-acquired — outpatient for mild case, inpatient for moderate to severe case such as hypoxemia, altered mental status, hypotension, significant co-morbid illness, and age extremes.
  • Nosocomial — patients already hospitalized

General Measures

  • Empiric antimicrobial therapy for most likely pathogen(s)
  • Consider oxygen for patients with cyanosis, hypoxia, dyspnea, circulatory disturbances or delirium
  • Mechanical ventilation for respiratory failure
  • Hydration
  • Analgesia for pain
  • Electrolyte correction
  • Respiratory isolation if TB is a possibility


Bedrest and/or reduced activity during acute phase


  • Nothing by mouth if there is incipient respiratory failure
  • Consider soft, easy-to-eat foods

Medications (Drugs, Medicines)

Drug(s) of Choice

Initial therapy

  • Usually empiric for most likely pathogens given clinical scenario (if specific etiology is identified, adjust antimicrobial therapy)
  • Otherwise healthy young adult with mild community-acquired pneumonia: erythromycin 500 po q6h; in those intolerant of erythromycin and in smokers [to treat H. influenzae], consider the new macrolides or doxycycline 1OOmg bid
  • Older patients or patients with preexistent illnesses, with mild community-acquired pneumonia: pneumococcal-active fluoroquinolone, telithromycin or amoxicillin-clavulanate with erythromycin or other macrolide
  • Patients with community-acquired pneumonia requiring hospitalization: a specific cephalosporin (cefotaxime, ceftriaxone or cefuroxime) or ampicillin-sulbactam plus macrolide; or a pneumococcal-active fluoroquinolone alone
  • For nosocomial pneumonia: either ceftazidime or an antipseudomonal penicillin (piperacillin, orticarcillin) plus an aminoglycoside. Vancomycin should be considered if strong suspicion of Staphylococcus aureus.

Therapy for specific organisms

  • S. pneumoniae: penicillin G or oral amoxicillin. If high incidence of penicillin resistant S. pneumoniae in the area, consider pneumococcal-active fluoroquinolone or telithromycin
  • H. influenzae: trimethoprim-sulfamethoxazole. For severe infections — cefotaxime, ceftriaxone, or carbapenems
  • S. aureus: nafcillin or vancomycin (if high incidence of methicillin resistant S. aureus)
  • Klebsiella species: carbapenems or 3rd generation cephalosporin
  • Pseudomonas: aminoglycoside plus antipseudomonal penicillin or ceftazidime

Moraxella catarrhalis: 2nd generation cephalosporin (cefuroxime axetil) or B-lactam/B-lactamase inhibitors

  • Chlamydia pneumoniae: doxycycline, fluoroquinolone
  • Mycoplasma pneumoniae: doxycycline
  • Legionella pneumophila: fluoroquinolone or azithromycin
  • Anaerobes: clindamycin or B-lactam/B-lactamase inhibitors

Contraindications: Allergy or likely cross-allergy to the prescribed antibiotic

Precautions: Possible significant sodium overload with antipseudomonal penicillins

Significant possible interactions: Refer to manufacturer’s literature

Alternative Drugs

  • S. pneumoniae: macrolide, doxycycline; cefotaxime. ceftriaxone or cefuroxime, linezolid, telithromycin
  • H. influenzae: cefuroxime; fluoroquinolones; extended macrolides; beta-lactam/beta-lactamase inhibitor, telithromycin
  • S. aureus: a first generation cephalosporin; clindamycin; linezolid
  • Klebsiella: fluoroquinolone
  • Pseudomonas: carbapenems, aztreonam, cefepime
  • Moraxella catarrhalis: trimethoprim- sulfamethoxazole; fluoroquinolone; cefixime, extended macrolide; telithromycin
  • Chlamydia pneumoniae: clarithromycin; azithromycin; erythromycin; telithromycin
  • Mycoplasma pneumoniae: clarithromycin; erythromycin; azithromycin or fluoroquinolone; telithromycin
  • Legionella pneumophila: clarithromycin; erythromycin; doxycycline

Patient Monitoring

  • If outpatient therapy, daily assessment of the patient’s progress, and reassessment of therapy if clinical worsening or no improvement in 48-72 hours
  • CXR take time to clear and may not show clearing, even though patient is improving. Repeat study about 6 weeks after recovery to verify the pneumonia was not caused by an obstructing endobronchial lesion in selected patients (smokers and older patients).
  • Repeating the cultures after treatment has been started is unnecessary unless there has been treatment failure or if treating TB

Prevention / Avoidance

  • Reduce risk factors where possible (quit smoking)
  • Bedridden and postoperative patients — deep breathing and coughing exercises; prevent aspiration during nasogastric tube feedings
  • Avoid indiscriminate use of antibiotics during minor viral infections
  • Annual influenza vaccine for high risk individuals
  • Polyvalent pneumococcal vaccine

Possible Complications

  • Empyema
  • Pulmonary abscess
  • Superinfections
  • Multiple organ dysfunction syndrome (MODS)
  • Adult respiratory distress syndrome (ARDS)
  • Post-pneumonic atelectasis may occur in 5-10% of children

Expected Course / Prognosis

  • Usual course — acute. In otherwise healthy individual, improvement seen and fever resolved in 1-3 days; sometimes up to 1 week
  • Overall attributable mortality is about 5% in community acquired; (=15% if hospitalized and < 1% if not hospitalized) 25-50% in nosocomial • Poorest prognosis — age extremes, positive blood cultures, low WBC, presence of associated disease, immunosuppression respiratory failure, inappropriate antecedent antibiotics, delayed treatment >8 hours


Associated Conditions

  • Tobacco smoking
  • Alcoholism
  • Upper respiratory infection

Age-Related Factors

Pediatric: Morbidity and mortality high in children under age 1

Geriatric: Morbidity and mortality high if > 70, especially with associated disease or risk factor

Pregnancy: N/A


  • Lobar pneumonia
  • Classic pneumococcal pneumonia

International Classification of Diseases

481 Pneumococcal pneumonia [Streptococcus pneumoniae pneumonia]

486 Pneumonia, organism unspecified

See Also

Pneumonia, viral Pneumonia, mycoplasma Rhodococcus infections

Other Notes

Pneumococcal vaccine for all adults over age 65 and children over 2 years (and adults) with risk (cardio, pulmonary or metabolic disorders); strongly consider in all adults age 50 and older.

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