Respiratory Infections

Evidence-Based Diagnosis and Stewardship for Respiratory Infections

Topic Overview

Respiratory infections are the most common acute reason for ambulatory care visits, making up a significant portion of a Family Nurse Practitioner's (FNP) daily caseload ^[5]. The FNP's primary challenge is distinguishing between self-limiting viral infections (e.g., common cold, acute bronchitis) and serious bacterial infections (e.g., Group A Strep pharyngitis, community-acquired pneumonia) that require targeted antibiotic therapy. Mastery of evidence-based guidelines (IDSA, CDC) for diagnosis and treatment is essential for optimizing patient outcomes and combating antimicrobial resistance ^[1].

Key Concepts & Definitions

• Upper Respiratory Infection (URI): Involves the nasal passages, sinuses, pharynx, larynx, and trachea. Common presentations include rhinosinusitis, pharyngitis, and laryngitis.
• Lower Respiratory Infection (LRI): Involves the bronchi, bronchioles, and alveoli. Includes acute bronchitis and pneumonia.
• Community-Acquired Pneumonia (CAP): Pneumonia acquired outside of a hospital or long-term care facility setting. The most common causative agent is Streptococcus pneumoniae ^[1].
• Atypical Pneumonia: Caused by organisms like Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Legionella pneumophila. Often presents with a dry cough and extrapulmonary symptoms.
• Antimicrobial Stewardship: A coordinated program that promotes the appropriate use of antimicrobials, improves patient outcomes, reduces microbial resistance, and decreases the spread of infections caused by multidrug-resistant organisms ^[3].

Core Principles: Pathophysiology & Transmission

1. Pathophysiology: Pathogens invade the respiratory mucosa, triggering an inflammatory cascade. This leads to vasodilation, increased capillary permeability, and recruitment of immune cells, resulting in the classic signs of infection (erythema, edema, exudate, fever).
2. Transmission: Most respiratory infections spread via respiratory droplets (coughing, sneezing) or direct contact with contaminated fomites. Mycobacterium tuberculosis is unique in that it is transmitted via airborne droplet nuclei (particles <5 microns) ^[5].
3. Stewardship Rule: The FNP must understand that antibiotics are almost never indicated for acute bronchitis (a predominantly viral illness) unless pertussis or influenza is confirmed. Overuse of antibiotics contributes directly to C. difficile colitis and resistant organisms like MRSA ^[1].

Signs, Symptoms, & Clinical Features

Differentiating between viral URI, bacterial pharyngitis, and CAP is critical.

• Viral URI/Rhinosinusitis: Nasal congestion, clear rhinorrhea, post-nasal drip, sneezing, low-grade fever. Symptoms typically peak at day 2-3 and resolve by day 7-10. Bacterial sinusitis is suspected if symptoms persist >10 days or worsen after initial improvement ("double worsening") ^[3].
• Group A Streptococcal (GAS) Pharyngitis: Sudden onset of severe sore throat, fever >100.4°F, tonsillar exudate, tender anterior cervical lymphadenopathy, and absence of cough ^[2].
• Community-Acquired Pneumonia (CAP): Acute onset of productive cough (purulent sputum), pleuritic chest pain, dyspnea, fever, crackles/rhonchi on auscultation, and tachypnea ^[1].
• Acute Bronchitis: Acute cough (with or without sputum), often following a URI. Fever is variable. The hallmark is the absence of pneumonia on chest X-ray ^[5].

Assessment, Diagnosis, & Evaluation

Pharyngitis: The Centor Score (Modified)

Use the Centor criteria to guide the need for rapid antigen testing or empiric antibiotics ^[2].

Community-Acquired Pneumonia: CURB-65 Severity Score

Determines the need for hospitalization ^[1].

• C: Confusion (new onset)
• U: Urea > 7 mmol/L (BUN > 20 mg/dL)
• R: Respiratory Rate > 30 breaths/min
• B: Blood Pressure (SBP < 90 mmHg or DBP < 60 mmHg)
• 65: Age > 65 years

Interpretation: Score 0-1: Outpatient management; Score 2: Short-stay admission or supervised outpatient; Score 3-5: Inpatient (consider ICU if score 4-5) ^[1].

Diagnostic Tools

• Rapid Strep Test (RADT): Highly specific (95%) for GAS. False negative rate is higher in children ^[2].
• Influenza/COVID-19 PCR: Gold standard for diagnosis. Antiviral therapy (oseltamivir/ritonavir-boosted nirmatrelvir) is most effective when started within 48 hours of symptom onset ^[4].
• Chest X-Ray (PA & Lateral): Indicated to confirm pneumonia when there is suspicion (fever + productive cough + focal findings on exam) ^[1].
• TB Screening: PPD (Mantoux) skin test or Interferon-Gamma Release Assay (IGRA/blood test). A positive test indicates infection, not necessarily active disease. High-risk groups include immunosuppressed, recent immigrants, and healthcare workers ^[7].

Treatment, Interventions, & Patient Care

Antibiotic Therapy

• GAS Pharyngitis:
  • First-Line: Penicillin VK (250mg TID or 500mg BID) or Amoxicillin (50mg/kg/day, max 1g) for 10 days ^[2].
  • PCN Allergic: Cephalexin (if no anaphylaxis) or Azithromycin (5 days) or Clindamycin. Note: Macrolide resistance is rising ^[2].
• Community-Acquired Pneumonia (Outpatient): ^[1]
  • No comorbidities: Amoxicillin (1g TID) OR Doxycycline (100mg BID) OR Macrolide (Azithromycin) if local resistance is low.
  • Comorbidities (COPD, DM, CHF, Malignancy): Combination therapy: Beta-lactam (Amoxicillin-clavulanate or Cefpodoxime) PLUS Macrolide. OR Monotherapy with a Respiratory Fluoroquinolone (Levofloxacin 750mg daily).
• Acute Bacterial Rhinosinusitis: Only treat if symptoms >10 days, severe (>102°F + purulent discharge for 3 days), or double worsening. First-Line: Amoxicillin-clavulanate (Augmentin) ^[3].

Antiviral Therapy

• Influenza: Oseltamivir (Tamiflu) 75mg BID x 5 days. Start within 48 hours for maximum benefit. Treatment is recommended for hospitalized patients regardless of time of onset ^[4].
• COVID-19: Ritonavir-boosted nirmatrelvir (Paxlovid) for high-risk patients within 5 days of symptom onset ^[4].

Supportive Care

• Hydration & Antipyretics: Acetaminophen or NSAIDs for fever and myalgias.
• Cough Suppressants: Dextromethorphan for dry, hacking cough. Expectorants (Guaifenesin) are minimally effective. Honey can be used for adults and children >1 year old.
• Bronchodilators: Inhaled beta-agonists (Albuterol) are useful if wheezing is present (e.g., acute bronchitis in asthma/COPD patients) ^[5].

Safety Precautions & Complications

• Complications of Untreated GAS: Acute Rheumatic Fever (valvular heart disease), Post-Streptococcal Glomerulonephritis, Peritonsillar Abscess. Key Exam Point: Treating Strep can prevent Rheumatic Fever but does not prevent Glomerulonephritis ^[2].
• Sepsis: Assess for qSOFA (quick Sequential Organ Failure Assessment): Altered mentation, RR >22, SBP <100. Two or more criteria indicate high risk for poor outcomes ^[5].
• Antibiotic Side Effects:
  • Penicillin Allergy: Rash, anaphylaxis (rare). Cephalosporins have ~10% cross-reactivity.
  • Fluoroquinolones: Black box warning for tendinitis/tendon rupture, neuropathy, CNS effects. Reserve for severe infections with no alternative ^[1].
  • C. difficile Colitis: Avoid fluoroquinolones and broad-spectrum antibiotics when possible.
• TB Reactivation: Patients on TNF-alpha inhibitors (e.g., for RA) or chronic high-dose steroids are at risk. Screen for Latent TB before initiating biologic therapy ^[7].

Exam Tips & High-Yield Points

• The #1 Rule: Do not prescribe antibiotics for acute bronchitis. The differential includes pertussis (paroxysmal cough +/- post-tussive emesis) and influenza.
• Strep Pharyngitis: You must know the Centor criteria (Fever, Exudate, Nodes, No Cough). Memory Aid: "FERNC" (like "fern").
• CAP: Empiric therapy depends on comorbidities. Memory Aid: "No co-morbid = Mac or Doxy. Co-morbid = Beta-lactam + Mac or FQ alone."
• Atypical Pneumonia: Think Mycoplasma in young, healthy adults with a dry, hacking cough. Treat with Macrolide or Doxycycline. CXR often looks worse than the patient appears.
• TB Screening: A positive PPD is defined by induration (not erythema). 5mm (HIV/immunosuppressed), 10mm (high risk), 15mm (low risk). QuantiFERON Gold is preferred for patients with BCG vaccination ^[7].
• Pertussis: Treat with Azithromycin and give prophylaxis to close contacts, regardless of vaccination status ^[6].

References

1. Metlay, J. P., Waterer, G. W., Long, A. C., et al. (2019). Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America. American Journal of Respiratory and Critical Care Medicine, 200(7), e45–e67. https://doi.org/10.1164/rccm.201908-1581ST
2. Shulman, S. T., Bisno, A. L., Clegg, H. W., et al. (2012). Clinical Practice Guideline for the Diagnosis and Management of Group A Streptococcal Pharyngitis: 2012 Update by the Infectious Diseases Society of America. Clinical Infectious Diseases, 55(10), e86–e102. https://doi.org/10.1093/cid/cis629
3. Chow, A. W., Benninger, M. S., Brook, I., et al. (2012). IDSA Clinical Practice Guideline for Acute Bacterial Rhinosinusitis in Children and Adults. Clinical Infectious Diseases, 54(8), e72–e112. https://doi.org/10.1093/cid/cir1043
4. Centers for Disease Control and Prevention. (2024). Influenza Antiviral Medications: Summary for Clinicians. https://www.cdc.gov/flu/hcp/antivirals/summary-clinicians.html
5. Harding, M. M., Kwong, J., Roberts, D., Hagler, D., & Reinisch, C. (2020). Lewis's Medical-Surgical Nursing: Assessment and Management of Clinical Problems (11th ed.). Elsevier.
6. Centers for Disease Control and Prevention. (2020). Pertussis (Whooping Cough) Treatment. https://www.cdc.gov/pertussis/hcp/clinical-care/index.html
7. U.S. Preventive Services Task Force. (2023). Screening for Latent Tuberculosis Infection in Adults: US Preventive Services Task Force Recommendation Statement. JAMA, 329(17), 1487–1494. https://doi.org/10.1001/jama.2023.4899