From the Guidelines
Viral pneumonia and bacterial pneumonia can be differentiated based on their distinct clinical hallmarks, with viral pneumonia typically presenting with a gradual onset of symptoms and bacterial pneumonia having an abrupt onset with high fever and productive cough. The diagnosis of viral versus bacterial pneumonia is crucial in guiding treatment decisions, as bacterial pneumonia requires appropriate antibiotic therapy, while viral pneumonia management is primarily supportive. According to the American Thoracic Society and Infectious Diseases Society of America guideline 1, procalcitonin levels can help distinguish between viral and bacterial etiologies, with levels of <0.1 mg/L indicating a high likelihood of viral infection and levels >0.25 mg/L indicating a high likelihood of bacterial pneumonia. However, a recent study 1 suggests that procalcitonin cannot be used alone to justify withholding antibiotics from patients with community-acquired pneumonia (CAP), and that clinical criteria, laboratory tests, and imaging should be used in combination to assess the likelihood of bacterial co-infection. Some key hallmarks of viral pneumonia include:
- Gradual onset of symptoms
- Low-grade fever
- Dry cough
- Headache
- Myalgia
- Fatigue
- Scattered rales and rhonchi with minimal consolidation on physical examination
- Normal or low white blood cell counts with lymphocytic predominance on laboratory tests
- Bilateral interstitial infiltrates with a diffuse, patchy pattern on chest imaging In contrast, bacterial pneumonia often presents with:
- Abrupt onset of symptoms
- High fever
- Productive cough with purulent sputum
- Pleuritic chest pain
- Sometimes hemoptysis
- Focal consolidation with bronchial breath sounds and egophony on physical examination
- Leukocytosis with neutrophil predominance on laboratory tests
- Lobar consolidation or segmental infiltrates on chest imaging It is essential to note that mixed viral-bacterial infections can occur and complicate the clinical picture, and that antibiotic therapy should be considered if there is a high suspicion of bacterial co-infection, especially in severely immunocompromised patients 1.
From the Research
Hallmarks of Viral Pneumonia
- Symptoms may include cough, fever, fatigue, and loss of appetite 2
- Children and the elderly may present with different symptoms, such as headache, nausea, abdominal pain, and absence of typical symptoms 2
- Diagnosis and treatment may involve antimicrobial therapy, with consideration of local bacterial pathogens and their antibiotic susceptibility and resistance profiles 2
Hallmarks of Bacterial Pneumonia
- May be caused by typical respiratory pathogens, as well as less common microorganisms and multidrug-resistant (MDR) germs 3
- Epidemiological and clinical risk factors can influence the microbiological cause of severe pneumonia 3
- Antimicrobials remain the mainstay of treatment, with optimization of antibiotic therapy through pharmacodynamic/pharmacokinetic properties 3
- Combination treatment with a beta-lactam plus a macrolide, such as ceftriaxone and azithromycin, may improve outcomes for elderly patients with community-acquired pneumonia (CAP) 4, 5, 6
Key Differences
- Viral pneumonia may have a more gradual onset and milder symptoms, while bacterial pneumonia can be more severe and life-threatening 2
- Bacterial pneumonia often requires antimicrobial therapy, while viral pneumonia may not respond to antibiotics 2
- The use of molecular diagnostic techniques can help identify the cause of pneumonia and guide treatment decisions 3