Pneumonia

Pneumonia presents with cough, fever, sputum production, and dyspnea. In community-acquired pneumonia (CAP), a specific cause is not determined in >50% of cases. Typical bacterial pathogens are S. pneumoniae, H. influenzae, S. aureus, and gram negative bacteria.

CASES/YEAR
10,000,000 (US); 200,000,000 (Global)
CATEGORY
Localized Infections
AGENT TYPE
Mixed
OTHER NAMES
Pneumonia, community-acquired; Pneumonia, hospital-acquired; Pneumonia, aspiration;
ACUITY
Acute-Moderate
INCUBATION
Estimated: 1 day to 2 months;
INITIAL SYMPTOMS
Cough, fever, sputum production, and dyspnea;
PRECAUTIONS
Standard for viral and bacterial not listed elsewhere; Droplet for Mycoplasma, H. influenzae in children, Meningococcal, and Streptococcus, group A; Droplet + Contact for Adenovirus; Contact for B. cepacia in patients with CF, including respiratory tract colonization; [CDC 2007 Guideline for Isolation Precautions]
COMMENTS
FINDINGS:
In community-acquired pneumonia (CAP), a specific cause is not determined in >50% of cases. Typical bacterial pathogens are S. pneumoniae, H. influenzae, S. aureus, and gram negative bacteria. Atypical organisms are M. pneumoniae, C. pneumoniae, Legionella species, and viruses (e.g., influenza, adenoviruses, and RSV). A good sputum sample has >25 WBCs and <10 epithelial cells per high-power field. Urine antigen tests for S. pneumoniae and Legionella are available. PCR of respiratory secretions has become the standard in the diagnosis of viral and atypical bacterial pneumonia. [Harrisons, p. 746-7] Causes of chronic pneumonia include bacteria (actinomycosis, nocardiosis, and melioidosis), mycobacteria (tuberculosis and other mycobacteria), fungi (aspergillosis, blastomycosis, coccidioidomycosis, cryptococcosis, histoplasmosis, sporotrichosis, paracoccidioidomycosis, and phaeohyphomycosis), and parasites (dirofilariasis, echinococcosis, filariasis, and paragonimiasis). [PPID, p. 933t] Weight loss is a symptom of chronic pneumonia. [PPID, p. 935] Elderly patients with pneumonia may present with delirium as well as the usual findings of pneumonia. [Cohen, 3rd Ed, p. 288] Radiographs are false negative in up to 30% of cases of Pneumocystis pneumonia. [ID, p. 470] Diarrhea, headache, bradycardia, and liver enzyme elevations are findings in legionellosis. Pharyngitis is an early symptom in pneumonia caused by mycoplasma or chlamydia. [PPID, p. 905-6]

SEVERITY:
CURB-65 has useful criteria for severity-of-illness: C = confusion (1 pt.); U = BUN > 19 mg/dl (1 pt.); R = RR >30 (1 pt.); B = BP <90/60 (1 pt.); Age >65 (1 pt.) If > 1 pt., then hospitalize. [IDSA/ATS Guidelines on the Management for CAP in Adults. 2007] Pathogens in nosocomial pneumonia are: S. aureus; Gram negative bacilli; Legionella spp; anerobes; and viruses; [ABX Guide] In community-acquired pneumonia, leukopenia is sign of poor prognosis. In chronic pneumonia, leukopenia suggests HIV infection. [PPID, p. 902, 935]

VIRAL PNEUMONIA:
Common viral causes include respiratory syncytial virus (RSV), adenoviruses, influenza viruses, metapneumovirus, and parainfluenza viruses. "Adenovirus, Epstein-Barr virus, and coxsackievirus are common viruses that rarely cause pneumonia. Seasonal influenza can rarely cause a direct viral pneumonia but often predisposes to the development of a serious secondary bacterial pneumonia. Varicella virus and hantavirus cause lung infection as part of adult chickenpox and hantavirus pulmonary syndrome. A coronavirus causes severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS)." [Merck Manual, p. 480-1] Viruses cause about 90% of pneumonia cases in children and 4% to 39% in adults. [5MCC-2020]

COMPLICATIONS:
Complications include lung abscesses, pleural effusions and rarely metastatic infections (e.g., brain abscess, endocarditis). [Harrisons, p. 748] Brain abscesses may complicate chronic pneumonia. [PPID, p. 935] Cranial nerve palsies and transverse myelitis are complications of mycoplasma pneumonia. [Cohen, 3rd Ed, p. 287]
DIAGNOSTIC
Exam: fever, tachypnea, and rales; Chest x-ray: infiltrate; Sputum for Gram stain and culture; Blood culture; Legionella and Pneumococcal urine antigens; [Harrisons, p. 747]
SCOPE
Global
SIGNS & SYMPTOMS
  • >arthralgia
  • >fatigue, weakness
  • >fever
  • >myalgia
  • >relative bradycardia
  • E pharyngitis
  • E rhinitis
  • G abdominal pain
  • G diarrhea
  • G liver function test, abnormal
  • G nausea, vomiting
  • H anemia
  • H leukocytosis
  • H leukopenia
  • H thrombocytopenia
  • N confusion, delirium
  • N headache
  • N lethargy
  • R chest pain
  • R cough
  • R dyspnea
  • R hemoptysis
  • R sputum production
  • R wheezing
  • X cystic or cavitary lesions
  • X hilar lymphadenopathy
  • X lung infiltrates
  • X pleural effusions
  • *acute renal failure
  • *ARDS
  • *arthritis
  • *brain abscess or lesion
  • *cranial neuropathy
  • *endocarditis
  • *meningitis
  • *myelitis
  • *pericarditis
  • *pneumonia
  • *pneumonitis
  • *pulmonary edema
  • *sepsis
  • *shock
  • *weight loss
ANTIMICROBIC

Yes

VACCINE

No

ENTRY
Inhalation, Ingestion, Needle (Includes Drug Abuse), Scalpel or Transfusion, Skin or Mucous Membranes (Includes Conjunctiva), Animal Bite, Swimming, Sexual Contact
VECTOR
Fleas, Biting Flies, Lice, Mites, Mosquitoes, Ticks
SOURCE
Person-to-Person, Human Fecal-Oral, Fecally Contaminated Soil, Animal Excreta, Animal Tissue, Soil or Dust (Ingesting or Inhaling), Eating Contaminated Food, Eating Contaminated or Infected Meat, Eating Infected or Toxin-Containing Fish, Eating Contaminated Mollusks or Crustacean, Eating Unpasteurized Milk or Cheese, Eating Contaminated Produce, Waterborne (Ingesting, Inhaling, or Swimming)
RESERVOIR
Birds and Poultry, Cattle, Goats and Sheep, Cats, Deer, Elk and Antelope, Dogs, Fish and Shellfish, Horses, Monkeys, Rabbits, Rodents, Swine, Human, Wild Animals
RISK FACTORS
  • AIDS patients
  • Cancer patients
  • Injection drug users
DRUG LINK
Merck Manual: Community-Acquired Pneumonia
REFERENCES FOR CASES/YEAR
1. (US) More than 10 million cases of pneumonia and 1 million hospitalizations every year in the US; [Cecil, 24th Ed, p. 588]
2. (Global) Lower respiratory tract infections caused 3.2 million deaths in 2011; 1.1 million children <5 years die every year; [Fact sheets from WHO 2013] Mortality of CAP for outpatients is <1%. [Gorbach, p. 321] In developing countries, case fatality rates for children for pneumococcal pneumonia are often over 10%. [CCDM, p. 465] Calculate: global cases/yr = 20 X US cases/yr.