This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
All of the following is used in preventing Legionella infection, EXCEPT: 
Select and explain. 
A. Heat at 50 Deg C, B. Hyperchlorination, C. Metal ions, D. Minimise the use of contaminated water
A: Heat at 50 Deg C
Answer: A: Heat at 50 Deg C 
Explanation: The prevention of legionellosis involves minimizing production of aerosols in public places from water that may be contaminated with Legionella. Prevention is complicated by the fact that, compared with other environmental bacteria, Legionella bacteria are relatively resistant to chlorine and heat. The bacteria have been isolated from hot water tanks held at over 50degC. Methods for decontaminating water systems are still under evaluation. Some outbreaks have been aboed by hyperchlorination, by correcting malfunctions in water systems, or by temporarily elevating the system temperature above 70degC. The installation of silver and copper ionization systems similar to those used in large swimming pools has been effective as a last reso in hospitals plagued with recurrent nosocomial legionellosis. Ref: Ray C.G., Ryan K.J. (2010). Chapter 34. Legionella. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.