Here are some good resources about health precautions to take prior to going to Hong Kong and during your time there. Consult your doctor or nurse practitioner to determine what, if any, measures you need to take.
I am not qualified to give medical advice, but I think it is a good idea to be sure that your tetanus-diphtheria and measles immunizations are up to date. There is also good reason to get a hepatitus A vaccination.
Centers for Disease Control -- East Asia recommendations -- excellent resource, please note the warnings on injuries. Traffic is the greatest hazard to your health.
World Health Organization -- China This site provides a macro picture of disease threats in China. You may find it interesting to compare disease patterns in China with those in the US and elsewhere.
Lonely Planet Press -- keeping healthy
Hong Kong Government health website
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