Persistence of Pseudomonas aeruginosa in a pulmonary nodule with late relapse

Area of Science:

• Infectious Diseases
• Pulmonology
• Transplantation Medicine

Background:

• Lung nodules are frequent diagnostic challenges in hematopoietic stem cell transplantation (HSCT) and solid organ transplantation (SOT).
• Pseudomonas aeruginosa (P. aeruginosa) is a recognized cause of lung abscess in immunocompromised patients, but its long-term persistence in pulmonary nodules is poorly understood.

Observation:

• A patient with acute pre-B-cell lymphoblastic leukemia post-allogeneic HSCT developed nodule enlargement and cavitation 10 months after transplantation.
• This nodule was a remnant of a presumed P. aeruginosa septic embolus from 2.5 months post-transplant.
• The nodule subsequently shrank to <1 cm with antibiotic treatment, remaining stable.

Findings:

• Transthoracic needle aspiration of the nodule yielded P. aeruginosa.
• Molecular typing confirmed the isolates were indistinguishable from those previously found in the patient's blood and bronchoalveolar lavage fluid.
• This demonstrates P. aeruginosa can remain viable within pulmonary nodules long after initial treatment.

Implications:

• Sub-centimeter pulmonary nodules post-P. aeruginosa infection may harbor viable organisms.
• These nodules can serve as a nidus for recrudescent infection in transplant recipients.
• This highlights the importance of considering persistent bacterial reservoirs in managing lung infections in immunocompromised populations.