If a patient had been diagnosed with pneumonia in May can there be a test now (September) to see if they had had Legionnaires’?
The blood serology test for antibodies to Legionella may be positive for many years after contracting Legionnaire’s disease. A positive test at a high antibody titer is circumstantial evidence for Legionnaires’ disease. Unfortunately, a negative test is not helpful, i.e. if the test shows a low titer, this result does not rule out Legionnaires’ disease. You may need a medical authority to assist you with interpretation of this test.