The yuck factor is HUGE with hotel room jacuzzis and public hot tubs, whether they are bubbling away at the Four Seasons, on the deck of a Celebrity Cruise, or next to the pool at the Y.  No one with a compromised immune system – the elderly, people on chemo or steroids, smokers, those with delicate urinary tracts or recovering from an illness, and certainly NOT babies – should use these public hot tubs.  As those relaxing bubbles burst around you, they may be releasing Legionnaire’s Disease, a very virulent form of pneumonia that kills.  By the time vulnerable people fail to respond to normal antibiotics to cure their fever, diarrhea, and flu-like symptoms, it’s often too late to diagnose and treat Legionnaire’s.  Hot tub rash and lung, eye, and staph infections are other problems that even healthy people can get from poorly maintained spas. 
And here’s the other problem – you know that tub in your suite at the cute little Bed and Breakfast?  Bacteria can lurk in the drain and the jets, and there are complaints on various travel sites that “black gunk,” hair, and skin flakes came shooting out of the jets after they filled the tub with fresh water.  Eeeuuuwww!  There are spa cleaners that supposedly disinfect, but one possible problem there is that you must not inhale the disinfectant that evaporates into the air as you run it in the hot swirling water.  Stay out of the bathroom, vent continuously, and let the stuff evaporate before you enter the room again.  If you love those jacuzzi bubbles, better get yourself a unit just for you and your honey to enjoy for fun, private times.
Then there’s the foot spa that you stick your feet in when you get a pedicure…
I’m sorry to be such a killjoy, ‘cause I love pampering myself, but at least inquire how the units are kept clean and bring your own nail tools.