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%).

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

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.

Laboratory

• 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

Imaging

• 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

Activity

Bedrest and/or reduced activity during acute phase

Diet

• 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

Miscellaneous

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

Synonyms

• 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.