When are antibiotics prescribed in cases of suspected or confirmed bacterial infections?

When to Prescribe Antibiotics

Antibiotics should be prescribed only when there is confirmed or high clinical suspicion of bacterial infection based on specific clinical, radiological, and laboratory criteria—not routinely for viral illnesses or fever alone. 1

Core Principles for Antibiotic Prescribing

Do NOT Prescribe Antibiotics For:

• Viral infections without bacterial superinfection 2
• Fever alone without other signs of bacterial infection 3
• COVID-19 patients who are mild to moderately ill without evidence of bacterial co-infection 1, 4
• Routine prophylaxis in most clinical situations 1

DO Prescribe Antibiotics When:

1. Confirmed Bacterial Infection

• Positive cultures identifying bacterial pathogens 1, 3
• Positive urinary antigen tests (pneumococcal, Legionella) 1
• Gram stain showing bacteria in appropriate clinical context 1

2. High Clinical Suspicion Based on Specific Criteria:

For Respiratory Infections:

• Radiological infiltrates consistent with bacterial pneumonia PLUS elevated inflammatory markers 1, 4
• Procalcitonin >0.5 ng/mL suggesting bacterial infection 1, 4
• Elevated WBC count and CRP in appropriate clinical context 1, 4
• Purulent sputum with increased volume AND increased dyspnea in COPD exacerbations 1

For Urological Infections:

• Clinical signs of urethritis with positive NAAT for gonorrhea or chlamydia 1
• Symptoms of prostatitis with supporting laboratory findings 1, 5
• Acute epididymitis with clinical findings of pain, swelling, and elevated temperature 1

3. Severe Illness or High-Risk Patients:

• Critically ill patients requiring ICU admission or mechanical ventilation 1, 4
• Immunocompromised patients (chemotherapy, transplant recipients, HIV/AIDS, prolonged corticosteroids) 1, 6
• Sepsis or septic shock 1
• Severe respiratory failure or hemodynamic instability 1

Diagnostic Workup BEFORE Prescribing

Always obtain these specimens before starting antibiotics: 1, 3

• Blood cultures (at least 2 sets)
• Sputum culture (if respiratory infection suspected)
• Urine culture (if urinary infection suspected)
• Pneumococcal urinary antigen test
• Legionella urinary antigen test (per local guidelines)
• Site-specific cultures (wound, CSF, etc.)

Common Pitfall: Starting antibiotics before obtaining cultures reduces diagnostic yield and leads to prolonged unnecessary therapy. 3

Empirical Therapy Selection Algorithm

Step 1: Assess Severity

• Mild-moderate illness → Follow local CAP guidelines, use narrow-spectrum agents 1, 4
• Severe/ICU → Broader coverage including antipseudomonal and potentially anti-MRSA 1, 4

Step 2: Consider Local Resistance Patterns

• Use Access group antibiotics (narrow-spectrum, lower resistance potential) as first choice when appropriate 1
• Reserve Watch group antibiotics (fluoroquinolones, carbapenems) for specific indications only 1
• Reserve group antibiotics only for confirmed/suspected multidrug-resistant organisms 1

Step 3: Site-Specific Considerations

Community-Acquired Pneumonia (non-ICU):

• Beta-lactam (amoxicillin-clavulanate or 3rd generation cephalosporin) 1, 4
• Consider adding coverage for atypicals only if specific risk factors present 1, 4

Community-Acquired Pneumonia (ICU):

• Antipseudomonal beta-lactam PLUS coverage for atypicals 1, 4
• Add anti-MRSA coverage in selected high-risk patients 1, 4

Urethritis:

• Ceftriaxone 1g IM/IV plus azithromycin 1g PO for gonococcal infection 1
• Doxycycline 100mg BID for 7 days or azithromycin for chlamydial infection 1, 7

Prostatitis:

• Ciprofloxacin as first choice for mild-moderate cases (if local resistance allows) 5
• Ceftriaxone or cefotaxime for severe cases 5

Duration and De-escalation Strategy

Stop Antibiotics When: 1, 4

• Cultures negative at 48 hours AND patient improving clinically
• Procalcitonin <0.25 ng/mL in appropriate clinical context
• Fever resolved and clinical stability achieved

Typical Treatment Durations:

• Uncomplicated bacterial pneumonia: 5-7 days 1, 4
• Legionella or S. aureus pneumonia: 21 days 1
• Mycoplasma or Chlamydia pneumoniae: 10-14 days 1
• Urethritis: 7 days (except single-dose regimens) 1

De-escalation: 3

• Switch from IV to oral when fever resolves and patient is clinically stable
• Narrow spectrum based on culture results
• Discontinue if infection ruled out

Critical Pitfalls to Avoid

1. Overuse in Viral Infections

• Bacterial co-infection rates in COVID-19 are <8% on admission 1
• Most respiratory illnesses are viral and do not benefit from antibiotics 2

2. Relying on Biomarkers Alone

• Do not use serum biomarkers alone to decide antibiotic initiation, especially in non-critically ill patients 1, 4
• Radiographic abnormalities in viral infections can mimic bacterial pneumonia 4

3. Inappropriate Broad-Spectrum Use

• Excessive use of broad-spectrum antibiotics increases costs and worsens outcomes 8
• 29.3% of hospitalized patients receive unnecessarily broad empirical therapy 8

4. Failure to Obtain Cultures

• 62.9% of MDRO-infected patients receive inappropriate therapy when cultures not obtained 8

5. Prolonged Unnecessary Therapy

• Continuing antibiotics despite negative cultures after 48 hours drives resistance 1