What is the diagnostic approach and treatment for an adult patient with no underlying medical conditions suspected of having pneumonia?

Diagnostic Approach for Pneumonia in Adults Without Comorbidities

In an adult patient without underlying medical conditions suspected of having pneumonia, obtain a chest radiograph immediately to confirm the diagnosis—this is mandatory and should be performed in all cases where pneumonia is suspected based on clinical presentation. 1, 2

Clinical Criteria for Suspicion

Suspect pneumonia when the patient presents with:

• Acute cough plus at least one of the following: new focal chest signs, dyspnea, tachypnea, or fever lasting >4 days 3
• Respiratory rate >20-24 breaths/min is highly suggestive and correlates with severity 4
• Abnormal vital signs (temperature >37.8°C, pulse >100/min, or respirations >20/min) are 97% sensitive for detecting pneumonia 5

Common pitfall: Up to 22% of patients with pneumonia have a completely normal chest examination, so the absence of lung findings does not rule out pneumonia. 5 Additionally, fever is absent in approximately 31% of pneumonia cases. 5

Radiographic Confirmation

• Posteroanterior and lateral chest radiograph is the gold standard and must be obtained in all suspected cases 3, 1, 2
• Look for consolidation, air space densities, infiltrates (alveolar or interstitial), or multilobar involvement 2, 6
• CT scanning is more sensitive but should be reserved for cases with negative radiographs despite high clinical suspicion or failure to respond to appropriate treatment 2

Adjunctive Diagnostic Testing

For outpatients with mild pneumonia, extensive microbiological testing is not routinely required, and empirical treatment should be initiated. 1 However, consider:

• CRP >30 mg/L significantly improves diagnostic accuracy when added to clinical criteria (increases ROC area from 0.70 to 0.77) 3
• Procalcitonin does not add meaningful diagnostic value over symptoms and signs alone 3

For hospitalized patients, obtain before starting antibiotics:

• Two sets of blood cultures (yield approximately 11%) 3, 1
• Expectorated sputum for Gram stain and culture (deep-cough specimen, rapidly transported) 3
• Complete blood count, basic metabolic panel, liver function tests, and oxygen saturation 3, 2
• COVID-19 and influenza testing when these viruses are circulating in the community 6

Critical point: Only 38% of hospitalized CAP patients have a pathogen identified, so negative cultures should not delay or alter empirical treatment. 6

Treatment Initiation

Antibiotics should not be delayed while awaiting diagnostic test results—mortality increases when the first antibiotic dose is delayed beyond 8 hours from hospital arrival. 1

For Outpatients (Mild CAP):

• Amoxicillin 1 gram PO three times daily is the first-line choice 4
• Alternative: Tetracycline or amoxicillin as first-choice agents 3
• In case of penicillin hypersensitivity: newer macrolides (azithromycin, clarithromycin, roxithromycin) in areas with low pneumococcal macrolide resistance 3
• Alternative fluoroquinolones: levofloxacin 750 mg PO once daily or moxifloxacin 400 mg PO once daily 4

For Hospitalized Patients (Without Risk Factors for Resistant Bacteria):

• β-lactam/macrolide combination therapy such as ceftriaxone plus azithromycin for a minimum of 3 days 1, 6
• This is the preferred regimen for patients without MRSA or Pseudomonas risk factors 1

Duration:

• Minimum 3 days for hospitalized patients with clinical improvement 6
• 5 days is recommended for non-severe CAP if clinical improvement occurs 7
• Usual duration is 7-10 days for most cases 8

Supportive Care

• Target SpO2 >92% and PaO2 >60 mmHg with supplemental oxygen 4
• Assess for volume depletion and provide IV fluids if needed 4
• Expect clinical improvement within 72 hours of starting antibiotics 4

Monitoring and Follow-up

• Switch from IV to oral antibiotics when the patient is hemodynamically stable, improving clinically, and afebrile 4
• Discharge criteria: clinically stable for 24 hours, afebrile, adequate oral intake, SpO2 >90%, and no more than one of the following: temperature >37.8°C, pulse >100/min, respiratory rate >24/min, systolic BP <90 mmHg 3, 4
• Follow-up at 6 weeks with chest radiograph for patients >50 years, smokers, or those with persistent symptoms 4

Avoid the outdated "typical vs atypical" classification—clinical presentation cannot reliably distinguish between bacterial and atypical pathogens. 1