Microbiology · Year 2 · from Microbiology
Case 1: Influenza Complicated by Bacterial Superinfection
Presentation
A 68-year-old woman with COPD and diabetes presents with 5 days of fever, myalgias, and dry cough that initially improved but then worsened over the past 2 days. She developed new productive cough with rust-colored sputum, shaking chills, and worsening dyspnea. She did not receive the influenza vaccine this season. Vital signs: temperature 39.8°C, heart rate 108 bpm, respiratory rate 28/min, oxygen saturation 89% on room air. Chest radiograph shows bilateral patchy infiltrates with a new right lower lobe consolidation. Nasal swab PCR is positive for influenza A.
Clinical Image
Chest radiograph demonstrating bilateral patchy infiltrates with right lower lobe consolidation, consistent with influenza pneumonia complicated by bacterial superinfection.
Image Source: Lecture image - influenza complications
Questions
- What complication has developed, and what organisms are most commonly responsible?
- Why are patients with influenza at increased risk for bacterial superinfection?
- What is the role of antiviral therapy at this stage of illness?
- How could this complication have been prevented?
Answers
- Complication and organisms: This patient has developed secondary bacterial pneumonia complicating influenza infection. The biphasic illness pattern (initial improvement followed by worsening) is classic for bacterial superinfection. The most common organisms are:
- Streptococcus pneumoniae (most common)
- Staphylococcus aureus (including MRSA - particularly concerning)
- Haemophilus influenzae
- Streptococcus pyogenes
The rust-colored sputum is suggestive of pneumococcal infection.
- Increased risk for bacterial superinfection: Influenza increases susceptibility to bacterial pneumonia through multiple mechanisms:
- Epithelial damage: Viral replication destroys respiratory epithelium and disrupts mucociliary clearance
- Upregulation of bacterial adhesion receptors on damaged epithelium
- Impaired immune function: Influenza suppresses macrophage and neutrophil function
- Neuraminidase: Viral neuraminidase exposes bacterial binding sites by cleaving sialic acid residues
- Inflammatory response: Dysregulated inflammation may contribute to tissue damage
- Role of antiviral therapy: Although typically most effective when started within 48 hours of symptom onset, antiviral therapy (oseltamivir) may still provide benefit in:
- Hospitalized patients (regardless of timing)
- Patients with severe or progressive illness
- Patients at high risk for complications
This patient should receive both oseltamivir AND empiric antibiotics covering typical bacterial pathogens (including S. aureus given severity). Antivirals can reduce viral shedding, potentially limiting further epithelial damage and improving outcomes even late in the illness course.
- Prevention:
- Annual influenza vaccination: Most important preventive measure, particularly for high-risk groups (elderly, chronic diseases)
- Pneumococcal vaccination: This patient should also receive pneumococcal vaccines (PCV20 or PCV15 + PPSV23)
- Early antiviral therapy: If influenza develops despite vaccination, early oseltamivir can reduce severity and complications
- Hand hygiene and respiratory precautions during influenza season