An outbreak of Legionella pneumophila
pneumonia occurred in 6 of 49 new renal transplant recipients over the course of 13 months. We compared infected patients (cases) and uninfected patients (controls) with respect to potential risk factors.
Corticosteroid use, need for
hemodialysis and number of days of
hemodialysis were significantly greater among the cases. Logistic regression analysis identified
corticosteroid dosage and number of days of
hemodialysis as independent risk factors.
Lymphopenia and monocytopenia were correlated with the amount of
corticosteroid administered and occurred to a greater degree in the cases. All clinical isolates were of L. pneumophila serogroup 1, subtype Philadelphia 1, which was also cultured from a recovery room sink outside the operating room where the transplants were done. Other areas of the hospital were colonized with other, heterogeneous strains of L. pneumophila. The organism was not eliminated from the hospital water supply despite
shock chlorination and superheating of water tanks. The epidemic ended when new transplant recipients routinely received prophylactic
trimethoprim-sulfamethoxazole (160-800 mg given orally once daily) while in hospital after
transplantation.
Corticosteroid-induced monocytopenia and
lymphopenia and the complement activation and monocyte depletion effects of
hemodialysis may combine to increase susceptibility to
Legionnaires' disease.