Persistence of Pseudomonas aeruginosa in a pulmonary nodule with late relapse.

Lung nodules are common diagnostic challenges in hematopoietic stem cell transplantation and solid organ transplantation. Pseudomonas aeruginosa is a known cause of lung abscess in these patients, but its ability to persist for months in a quiescent lung nodule and later cause recurrent infection is not well known or documented. A patient with a history of acute pre-B-cell lymphoblastic leukemia had enlargement and cavitation of a small right upper lobe pulmonary nodule 10 months after allogeneic hematopoietic stem cell transplantation. The nodule was the remnant of a presumed P. aeruginosa septic embolus that occurred 2.5 months after transplantation. With antibiotic treatment, the nodule had shrunk in size to <1 cm and remained stable. Transthoracic needle aspiration grew P. aeruginosa indistinguishable by molecular typing from isolates obtained 7.5 months earlier from blood and bronchoalveolar lavage fluid. Sub-centimeter pulmonary nodules attributable to previously treated P. aeruginosa may harbor viable organisms and lead to recrudescent infection.