Can Moraxella catarrhalis cause ground glass opacity (GGO)?

Moraxella catarrhalis and Ground Glass Opacity

Yes, Moraxella catarrhalis can cause ground glass opacity (GGO) on chest imaging, particularly in elderly patients and those with underlying pulmonary conditions such as emphysema. 1

Radiological Findings of M. catarrhalis Infection

Common CT Findings

• Ground-glass opacity (91% of cases) 1
• Bronchial wall thickening (78% of cases) 1
• Centrilobular nodules (72% of cases) 1
• Predominantly peripheral distribution in the lung parenchyma (91% of cases) 1

The thin-section CT findings in M. catarrhalis pulmonary infection are distinctive, with the triad of ground-glass opacities, bronchial wall thickening, and centrilobular nodules being highly characteristic. These findings are typically distributed in the peripheral lung regions 1.

Patient Demographics and Risk Factors

M. catarrhalis pulmonary infections with GGO are most commonly observed in:

• Elderly patients (mean age 74.9 years) 1
• Patients with underlying pulmonary emphysema (68% of cases) 1
• Patients with cardiovascular disease (40% of cases) 1
• Patients with malignant disease (38% of cases) 1

Clinical Significance

M. catarrhalis is an important respiratory pathogen that can cause:

• Acute respiratory infections 2
• Exacerbation of chronic obstructive pulmonary disease 1
• Both community-acquired (31%) and nosocomial infections (69%) 1

Differential Diagnosis

When evaluating ground-glass opacities on chest imaging, it's important to consider other causes:

1. Viral pneumonias:

   • COVID-19 (typically bilateral, peripheral, patchy GGOs) 3, 4
   • Influenza virus 4
   • Cytomegalovirus 4

2. Fungal infections:

   • Invasive aspergillosis (often with "halo sign") 3
   • Mucormycosis (may present with "reversed halo sign") 3

3. Non-infectious causes:

   • Pulmonary edema 4
   • Alveolar hemorrhage 4
   • Pulmonary infarction 4
   • Hypersensitivity pneumonitis 5
   • Cryptogenic organizing pneumonia 5

Diagnostic Approach

When M. catarrhalis is suspected as the cause of GGO:

1. Imaging:

   • High-resolution CT (HRCT) is superior to chest X-ray for detecting and characterizing GGOs 5
   • Look for the characteristic triad: ground-glass opacities, bronchial wall thickening, and centrilobular nodules 1

2. Microbiological confirmation:

   • Respiratory cultures (sputum, bronchial aspirate, or bronchoalveolar lavage)
   • Blood cultures in severe cases (though bacteremia is rare) 6, 7

Treatment Considerations

M. catarrhalis has high rates of beta-lactamase production (>80% of strains), making it resistant to ampicillin and other penicillins 2. Effective antibiotics include:

• Amoxicillin/clavulanic acid (100% sensitivity) 2
• Cefuroxime (99% sensitivity) 2
• Ciprofloxacin (99% sensitivity) 2
• Erythromycin (93% sensitivity) 2

Clinical Pearls and Pitfalls

• Pearl: The peripheral distribution of GGOs in M. catarrhalis infection can help differentiate it from other bacterial pneumonias that often have more central or diffuse patterns.
• Pitfall: During the COVID-19 pandemic, M. catarrhalis infections may be misdiagnosed as COVID-19 due to similar GGO patterns. Always consider bacterial pathogens, especially in patients with COPD exacerbations 4.
• Pearl: Absence of mediastinal or hilar lymphadenopathy is typical in M. catarrhalis infection, which can help differentiate it from some other causes of GGO 1.
• Pitfall: Empiric use of penicillin, ampicillin, or amoxicillin alone is not recommended due to high rates of beta-lactamase production 7.