From what I can recal it comes from drinking water infected with the bacteria or inhaling vapor from a contaminated source.
I did a serch and got this:
Quote:
We reviewed seven cases that had been reported and found recurrence of Legionella pneumonia possible after a successful treatment, especially for immunocompromised hosts. Early empirical therapy with erythromycin is recommended.
|
from
http://www.vghtpe.gov.tw/~cmj/5705/570509.htm
and
Quote:
Contracting Legionnaires' disease a second time is extremely rare. We have never encountered such a case. Thus, it seems likely that there is some immunity after the patient experiences the first infection. The most common risk factor is cigarette smoking. So, any patient who has contracted Legionnaires' disease (or any other type of pneumonia) should immediately quit smoking.
|
from
http://www.legionella.org/general_info.htm#n1
So your immune system either lost it's anti-bodies (or never had them) or was weakened by something else which allowed the bacteria to effect you a second time.
Wish you good health soon.