Presentation
Presents to emergency during Legionella outbreak with 4 day history of fever, cough productive of white sputum and asthma exacerbation.
Patient Data
Subtle patchy ill-defined nodular opacification in the lung bases.
Asymmetric increased attenuation in the left hilar region.
Otherwise normal.
Multifocal areas of bronchopneumonia:
thickened bronchial walls leading into the affected areas
peribronchial consolidation with fuzzy margins
ill-defined ground-glass opacity in the right lower lobe
focal confluent subpleural right lower lobe consolidation
Airways are normal in unaffected areas. No effusions.
The left hilum is normal. No lymphadenopathy.
He was treated for bronchopneumonia with reactive airways disease:
Prednisone 50mg orally in the morning, for 5 days
Amoxicillin 1g three times daily, for 5 days
Doxycycline 100mg twice daily, for 5 days
Albuterol 6 puffs four times daily, then aim to wean as symptoms resolve
Ipratropium bromide 6 puffs, four times a day, then aim to wean as symptoms resolve
Rapid urine Legionella antigen was negative and he was discharged home the same day.
Respiratory RT-PCR on respiratory secretions was positive for hMPV.
Case Discussion
Worsening symptoms during a well-publicized Legionella outbreak prompted the patient to attend the emergency department and he was admitted for assessment. Asthmatics are predisposed to develop both bacterial and viral pneumonias. The chest radiograph showed subtle patchy opacity which could easily have been overlooked, whereas the CT scan only 2 hours later was markedly abnormal. Looking at the coronal MIPs you would think that the consolidation would have been obvious on X-ray.
It was important to exclude Legionella infection which is resistant to beta-lactam antibiotics and is often rapidly progressive, causing severe pneumonia and extrapulmonary disease. The rapid L. pneumophila urinary antigen test result is available within minutes of processing and was negative in this case. This test is specific and usually positive at presentation in Legionella, however it is designed to detect serogroup 1 and can be negative for other serogroups.
Human metapneumovirus (hMPV) respiratory RT-PCR came back positive later that day. HMPV typically presents with URTI symptoms which can progress to bronchiolitis, wheezing and bronchopneumonia. Up to 2/3 of asthma exacerbations are due to a viral infection which enhances the response to allergens and causes airway inflammation. (Rhinovirus is the main culprit.) Asthma attacks are more frequent following recovery from viral infections and lung function may subsequently deteriorate 1.
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