The good news: Legionnaires' Disease is not person-person communicable.
Also good: it's bacterial, and treatment with antibiotics helps.
The bad news: the bacterium loves warm, stagnant water. Most outbreaks typically get traced back to contaminated air conditioning condensation.
25 years ago, a family member of mine got it from air conditioner condensation drops hitting her on the head while simply walking down the street (not in HK). She was in the hospital for quite a while with bad pneumonia. It's not fun. Hence I get pretty pissed off in the summer here, what with all the "air con rain" we get. I usually wear a hat for protection.
The contaminated water source needs to be found and cleaned out. Hopefully that happens soon.