Persistence of positivity for the Legionella urinary antigen?

We had a patient test positive by urine antigen in January who is now testing positive again 4 months later. If recurrence is rare, is there a specific time period that the test will convert to negative following the disease? Does a persistently positive test imply that Legionella infection still persists? Or does it imply that it wasn’t completely eradicated from her system?

Prolonged urinary antigen excretion has been reported. Most of the patients that we have evaluated converted to urinary antigen negative between 30-60 days. Factors related to prolonged excretion have included severity of illness and immunosuppression.

This was recently reviewed – Sopena N, Sabria M, et al. Factors related to persistence of Legionella urinary antigen excretion in patients with Legionnaires’ disease. Eur. J. Clin. Microbiol. Infect. Dis. 2002. 21:845-848.