Is it common for a person to have a blood test positive for Legionella without a history of illness? Is there any reason for concern for future illness?
The blood test (antibody serology) is most accurate when a person is ill with pneumonia. If the person has no pneumonia and does not have an abnormal chest x-ray, this person may have encountered Legionella many years ago and is ok now.
Based on our studies, we suspect that presence of antibody may be protective, since we never encountered patients who have contracted Legionnaires’ disease twice.