If you are visiting the "major" cities then general medicines should be enough. The parts you're going are probably as modern and clean as it can get in HK. Or let's say it won't be worse than the dirtiest part of where you are from.

It's just common sense to stay safe and maintain a good level of personal hygiene anywhere you go. Drink only bottled drinks. Wash hands before food, or use moist tissues (is there a name?) if you don't have water. It'd be your own risk if you're eating streetfood (YET most of the time the risk is well worth taking!!)...

The only people I met who've taken Malaria meds travelled to Laos (met them in Vietnam) - they also said they were the only one they know who've taken them - and feel stupid doing so. I'd be more worried about digestion problems...