Lesson 6.2: Pulmonary Infections

Introduction

In this lesson, we will explore pulmonary infections, including community-acquired pneumonia (CAP), hospital-acquired pneumonia (HAP), tuberculosis (TB), and other respiratory infections. Understanding the severity of these infections and how to manage them is critical for effective patient care. We will dive into diagnostic strategies, empiric therapy options, and isolation precautions.

Learning Objectives

By the end of this lesson, you will be able to:

• Explain the differences between community- and hospital-acquired pneumonia, tuberculosis, and other respiratory infections.
• Assess the severity of respiratory infections and make site-of-care decisions.
• Select appropriate empiric and targeted therapy.
• Identify the need for and implement infection control measures.
• Understand the core concepts and terminology related to pulmonary infections.

Community-Acquired Pneumonia (CAP)

Definition and Causes

Community-acquired pneumonia is defined as pneumonia acquired outside of healthcare settings. It usually presents with an acute onset of cough, fever, chills, and difficulty breathing. The most common pathogens responsible for CAP include:

• Bacteria: Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, and Legionella pneumophila.
• Viruses: Influenza virus, Respiratory Syncytial Virus (RSV), and coronaviruses.

Diagnosis

The diagnosis of CAP is based on clinical presentation, physical examination, and imaging studies.

1. Clinical Presentation: Patients typically have symptoms like cough, purulent sputum, and dyspnea.
2. Physical Examination: Findings may include increased tactile fremitus, dullness to percussion, and decreased breath sounds over the affected lung area.
3. Imaging: Chest X-ray often shows lobar consolidation or diffuse infiltrates.

Severity Assessment

The severity of CAP can be assessed using the CURB-65 criteria, which includes:

• Confusion
• Urea > 7 mmol/L
• Respiratory rate ≥ 30 breaths/min
• Blood pressure (systolic < 90 mmHg or diastolic ≤ 60 mmHg)
• Age ≥ 65 years

Each positive criterion adds one point to the total score. A higher score indicates a greater risk for mortality and may impact management decisions.

Empiric Therapy

Empiric therapy for CAP generally depends on the severity assessed by the CURB-65 score:

• Low Risk (0-1 points): Amoxicillin 1 g three times daily or doxycycline 100 mg twice daily.
• Moderate Risk (2 points): Amoxicillin-clavulanate 875 mg/125 mg twice daily or a respiratory fluoroquinolone like moxifloxacin 400 mg once daily.
• High Risk (3 points or more): Combination therapy with a beta-lactam (like ceftriaxone) and a macrolide (like azithromycin).

Worked Example 1

Case: A 70-year-old male presents with fever, cough, and confusion (C). His creatinine level is 1.2, respiratory rate is 28, heart rate is 110, and blood pressure is 85/55.

• CURB-65 Score: 3 (C, RR, BP)
• Assessment: High risk for mortality
• Management: Initiate combination therapy with ceftriaxone and azithromycin.

Hospital-Acquired Pneumonia (HAP)

Definition and Causes

HAP occurs in patients who have been hospitalized for 48 hours or more, and it is associated with various pathogens, including multidrug-resistant bacteria. Common pathogens include:

• Staphylococcus aureus (including MRSA)
• Pseudomonas aeruginosa
• Klebsiella pneumoniae

Diagnosis and Severity Assessment

Diagnosis relies on similar methods as for CAP, with the distinction of considering the patient's hospitalization history. Severity can be assessed using the same CURB-65 criteria alongside comorbid conditions.

Empiric Therapy

Initial treatment for HAP should cover resistant organisms using:

• Moderate Risk: Piperacillin-tazobactam or cefepime.
• High Risk (e.g., septic shock): Use two agents that cover gram-negative and MRSA (e.g., vancomycin + either a piperacillin-tazobactam or cephalosporin).

Worked Example 2

Case: A 50-year-old female has fever and cough on day 4 of hospitalization for elective surgery. Chest X-ray shows new infiltrates.

• CURB-65 Score: 0 (no confusion, BP normal)
• Assessment: Moderate risk; start treatment with piperacillin-tazobactam and consider MRSA coverage with vancomycin due to recent surgical history.

Tuberculosis (TB)

Definition and Causes

Tuberculosis is a contagious infection caused by _Mycobacterium tuberculosis_, primarily affecting the lungs but can impact other organs. Risk factors include immunosuppression, travel to endemic areas, and close contact with infected individuals.

Diagnosis

Diagnosis requires a high index of suspicion and can involve:

• Mantoux Test: Intradermal PPD test to identify exposure.
• Chest X-ray: May reveal cavitary lesions or infiltrates.
• Sputum Analysis: Acid-fast bacilli (AFB) smear and culture for mycobacteria.

Severity Assessment

Patients with active TB may present with hemoptysis, night sweats, weight loss, and prolonged cough. Severity can be assessed by symptom presence and extent of pulmonary involvement shown in imaging.

Empiric Therapy

Standard initial therapy for drug-susceptible TB includes:

• Isoniazid (INH)
• Rifampin (RIF)
• Pyrazinamide (PZA)
• Ethambutol (EMB)

This is typically continued for 2 months, followed by 4 months of INH and RIF.

Worked Example 3

Case: A patient presents with cough, weight loss, and hemoptysis in a high TB prevalence region. X-ray reveals cavitary lesions.

• Diagnosis: Active TB confirmed with sputum culture.
• Management: Start with the four-drug regimen (INH, RIF, PZA, EMB).

Other Respiratory Infections

Viral Infections

Besides pneumonia and TB, other viral infections can cause respiratory illness. Common viruses include:

• Influenza
• RSV

Diagnosis and Management for Viral Infections

While diagnosis may include rapid antigen tests or PCR, management focuses on supportive care. Antiviral medications, such as oseltamivir for influenza, may be indicated depending on symptom severity and risk factors.

Conclusion

In conclusion, managing pulmonary infections involves understanding the causative pathogens, assessing severity, and implementing appropriate empiric therapy. A thorough evaluation and a strategic approach will significantly enhance patient outcomes in these common yet serious conditions.

Study Notes

• Community-acquired pneumonia (CAP) is distinct from hospital-acquired pneumonia (HAP).
• CURB-65 helps assess CAP severity.
• Empiric therapy varies based on risk.
• Tuberculosis diagnosis includes Mantoux test and sputum analysis.
• Viral respiratory infections require supportive management and may need antiviral treatment.