Mr Jones said the ideal temperature for bacteria growth was between 20C and 45C. It was not unusual to find the bacteria in a shower head, he said.
"That is certainly a risk - regular cleaning of the shower head is recommended.
"The bacterium gets aerialised, that is one of the reasons you can catch it in the shower because it goes into little droplets that can be breathed in."
There was no record of it being transmitted through sneezing, he said.
People were more vulnerable if they were very young, very old, had a chronic illness or smoked.
The hospital had seen two cases of the disease since May. In both, Legionella was found in the victims' water supply.
The woman, who works for Pan Pac, was now in a stable condition in a general ward.
The other victim was a man in his 80s, who lived on town water and whose thermostat was set at the correct level.
Mr Jones said it was possible his thermostat was faulty. He was admitted in late April and discharged early May.
There was one recorded case of Legionnaires disease in Hawke's Bay last year.
Mr Jones urged people to check and adjust their hot water cylinder's thermostat to 60C.
"If you are not sure how to do that, you should get a plumber to do that for you."
Measuring hot water temperatures from taps can be inaccurate - home hot water cylinders are required to have tempering valves installed to prevent scalds.
The disease was named after a 1976 outbreak in the United States, following an American Legion convention in Pennsylvania. Twenty-five people died and 130 were hospitalised. The bacterium was traced to the cooling tower of the hotel's air conditioning system.
