Communicable Diseases in Phuket

Dengue fever:

The disease has been on the increase in Thailand. The dengue-carrying mosquito, Aedes aegypti, is most active during the day, particularly at dawn and dusk. The mosquito lays it eggs in water, so the risk of dengue is higher during the rainy season from May to October. The disease is rarely fatal but there is no cure.

The risk of catching dengue fever in Phuket is quite remote. However, it is not a disease you want to catch and there is no vaccine, so you should use insect repellent whenever possible to be on the safe side.
(Further reading: http://www.medicinenet.com/dengue_fever/article.htm).

Avian Influenza (Bird Flu):

The World Health Organization currently does not recommend any travel restrictions of travellers to areas affected with avian influenza, nor does it recommend screening of travellers from affected areas.

However, as a precaution you should avoid bird markets and farms, or anywhere you might come into contact with live poultry.
(Further reading: http://www.who.int/influenza/human_animal_interface/en/).

HIV:

Thailand has an epidemic of HIV infection and AIDS. Heterosexual transmission accounts for most HIV infections. HIV is common among sex workers of both sexes. Visitors are not particularly at risk unless they engage in sexual intercourse with strangers. If you don’t wear a condom, you are asking for it.
(Further reading: http://www.avert.org/aidsthai.htm).

Malaria:

According to the WHO, “there is no risk in cities and the main tourist resorts (e.g. Bangkok, Chiang Mai, Pattaya, Phuket, Samui)”. However, if you are travelling to remote areas in Thailand more caution should be exercised.You should consider taking preventive medication, though the best way to avoid the disease is not to get bitten. The malaria carrying mosquitoes are only active at night so this is the time which you need to be most watchful. Use insect repellent, sleep in air-conditioned rooms or under a mosquito net, and keep covered as much as possible.
(Further reading: http://www.searo.who.int/EN/Section10/Section21/Section340_4027.htm).