• Clinical science



Pneumonia is a respiratory infection characterized by inflammation of the alveolar space and/or the interstitial tissue of the lungs. In industrialized nations, it is the leading infectious cause of death. Pneumonia is commonly transmitted via aspiration of airborne pathogens (primarily bacteria) but may also result from the aspiration of stomach contents. The spectrum of causal pathogens is mainly determined by patient age, immune status, and where the infection was acquired (community-acquired or hospital-acquired). Pneumonia is also classified based on clinical features as either typical and atypical; each type has its own spectrum of commonly associated pathogens. Typical pneumonia presents with sudden onset of malaise, fever, and a productive cough. On auscultation, crackles and bronchial breath sounds are audible. Atypical pneumonia, on the other hand, presents with gradual onset of unproductive cough, dyspnea, and extrapulmonary manifestations. Auscultation is typically unremarkable. In reality, some patients may present with elements of both types. Diagnostics include blood tests for inflammatory parameters and pathogen detection in blood, urine, or sputum samples. Chest x-ray in cases of typical pneumonia shows extensive opacity restricted to one lobe, while atypical pneumonia presents with diffuse, often subtle infiltrates. A newly developed pulmonary infiltrate on chest x-ray in combination with the clinical features confirms the diagnosis. Management consists of supportive measures, such as oxygen administration or physiotherapy, and antibiotic treatment. Antibiotics are initially administered empirically and later adapted based on the results of bacterial culture.





Type of pneumonia Common pathogens
Community-acquired pneumonia Typical pneumonia
Atypical pneumonia
Hospital-acquired pneumonia
Special groups
Pneumonia in immunocompromised patients
Pneumonia in newborn infants
Recurrent pneumonia

Routes of infection

  • Most common: microaspiration (droplet infection) of airborne pathogens or oropharyngeal secretions
  • Aspiration of gastric acid (Mendelson's syndrome) , or of food or liquids
  • Hematogenous dissemination in rare cases

Risk factors




Clinical features

Typical pneumonia

Typical pneumonia presents with a sudden onset of symptoms caused by lobar infiltration.

Suspect bacterial pneumonia in immunocompromised patients with acute high fever and pleural effusion!

Atypical pneumonia

Atypical pneumonia typically takes an indolent course (slow onset) with an emphasis on extrapulmonary symptoms; . Common pathogens include mycoplasma, legionella, chlamydiae, and viruses such as RSV, influenza, CMV, and adenovirus.

  • Low-grade fever
  • Non-productive, dry cough
  • Dyspnea
  • Common extrapulmonary features include fatigue, headaches, sore throat, myalgias, malaise
  • Auscultation often unremarkable

A clear distinction between typical and atypical pneumonia is not always possible based solely on the symptoms. As both forms may be caused by any pathogen, the distinction has little bearing on therapeutic decisions!


Subtypes and variants

Aspiration pneumonia

  • Definition: Aspiration is the inhalation of foreign material into the respiratory tract. It often occurs after instrumentation of the upper airways or esophagus (e.g., upper GI endoscopy), or secondary to vomiting and regurgitation of gastric content.
  • Risk factors
  • Pathogens: mixed infections with anaerobic organisms are common (e.g., Klebsiella)
  • Clinical findings
    • Immediate symptoms: bronchospasms ; , crackles on auscultation, hypoxemia with cyanosis
    • Late symptoms: fever, shortness of breath, cough with foul-smelling sputum
  • Diagnosis
    • Arterial blood gas analysis (↓ PaO2, pH < 7.35, PaCO2 > 45 mm Hg)
    • Radiologic imaging: The lung region in which the infiltrates are seen in depends on the patient's position on aspiration. :
      • Supine position: superior segment of the right lower lobe (most common site of aspiration)
      • Standing/sitting: posterior basal segment of the right lower lobe
      • Right lateral decubitus position: posterior segment of the right upper lobe or right middle lobe
  • Management
  • Prevention: optimize therapy and/or prophylaxis of underlying causes to reduce the risk of aspiration

Pathogen-specific pneumonia

Lung abscess



Laboratory tests


A newly developed pulmonary infiltrate on chest x-ray in a patient with the classic symptoms of pneumonia confirms the diagnosis!

  • Thorax CT
    • Indications: inconclusive chest x-ray, recurrent pneumonia
    • Advantages: more reliable evaluation of circumscribed opacities, pleural emphysema, or sites of colliquation

Typical pneumonia usually appears as a lobar pneumonia on x-ray, while atypical pneumonia tends to appear as interstitial pneumonia. However, the underlying pathogen cannot be conclusively identified based on the imaging results!

Further diagnostics

The following tests are not part of the initial diagnostic workup; they are predominantly used for further investigation if the results of previous tests are negative or inconclusive.

  • Sputum : testing for multiresistant pathogens ; severe, rapid progressive nosocomial pneumonia
  • Pleurocentesis
    • pH metry value (normally 7.60–7.64)
    • Leukocyte count > 1000 WBCs/mm3 and protein levels (> 1-2 g/dL)
    • Inoculation of blood cultures with the puncture fluid and subsequent analysis
  • Bronchoscopy: indicated to visualize and biopsy a central mass discovered on CT imaging, or if CT results are inconclusive



Criteria for hospitalization

  • Based on CURB-65 score (or CRB-65 score (without U) if it is not possible to measure urea)
    • Confusion (disorientation, impaired consciousness)
    • Urea > 7 mmol/L (20 mg/dL)
    • Respiratory rate ≥ 30/min
    • Blood pressure: systolic BP ≤ 90 mm Hg or diastolic BP ≤ 60 mm Hg
    • Age 65 years
    • Interpretation
      • Each finding is appointed 1 point; max. 5 points possible
      • CURB-65 score ≤ 1: The patient may be treated as an outpatient.
        • A patient with a CRB-65 score of 0 may be treated as an outpatient.
      • CURB-65 score ≥ 2: Hospitalization is indicated.
        • A patient with a CRB-65 score ≥ 1 should be admitted for hospital treatment.
      • CURB-65 score ≥ 3: ICU-care should be considered.

Any patient being treated in a primary care setting should be reexamined after 48–72 hours to evaluate the efficacy of the prescribed antibiotic!

General measures

Medical treatment of pneumonia

As laboratory results with definite pathogen identification may take time to obtain, initial empiric antibiotic treatment with broad coverage is recommended.

Community-acquired pneumonia
Treatment parameters Regimen
Outpatient treatment
  • Patients without risk factors
Inpatient treatment
  • Non-ICU treatment
Special cases
  • If MRSA is suspected

Antibiotic treatment may be terminated 2–3 days after the fever subsides. In cases of community-acquired pneumonia that can be treated in the outpatient setting, seven days of antibiotic treatment are usually sufficient!

Hospital-acquired pneumonia

Hospital-acquired pneumonia
Profiles Regimen
Patients without risk factors for multiresistant pathogens

Patients with risk factors for multiresistant pathogens

Hospital-acquired pneumonia
Treatment parameters Regimen
Low/moderate risk of mortality Patients without risk factors for multiresistant pathogens
Patients with risk factors for multiresistant pathogens*
High risk of mortality or history of recent IV antibiotic use (< 90 days)

* Risk factors include: recent IV antibiotic treatment; hospitalization (on ICU); colonization with multiresistant pathogens; structural lung disease


Nonresponsive or progressive pneumonia

Monitoring treatment outcome

Evaluate therapeutic success 48–72 hours after initiation of treatment.

  • Criteria indicating stabilization
    • Improved consciousness level
    • Normalization of heart rate (≤ 100/min) and respiratory rate (≤ 24/min)
    • Normotension (systolic blood pressure ≥ 90 mm Hg)
    • Abatement of fever (≤ 38°C, ≤ 100.4°F)
    • Sufficient oxygenation (pO2 ≥ 60 mm Hg or SaO2 ≥ 90%, respectively)
  • Laboratory analysis: CRP control recommended on day 4 of treatment

CRP has a relatively long half-life of ∼ 24 hours, and levels often lag behind symptom improvement. Therefore, early laboratory controls of CRP are often still elevated or increase further. In contrast, the WBC is less specific but responds more rapidly!

Nonresolving or progressive pneumonia

Progression of infiltrates in follow-up chest x-rays are only considered signs of progressive pneumonia if the patient also shows signs of deterioration!


Pathogen Recommended antibiotic escalation therapy
Pseudomonas aeruginosa
Atypical pathogens
MRSA (see nosocomial infections)



We list the most important complications. The selection is not exhaustive.