Food and waterborne diseases are a primary cause for ill health in travellers. Visitors should only drink bottled water, avoid ice in drinks, and take care to eat well-cooked food. Cholera is regarded as a serious risk and precautions are advised, while typhoid is more of a problem in rural areas. Yellow fever vaccination certificates are required by travellers coming from infected areas. Malaria and dengue fever are a risk throughout the year. Travellers are strongly advised to take out good travel insurance, and seek medial advice at least three weeks before leaving for Sri Lanka. Following the tsunami on the 26 December 2004, there is a real risk of disease in affected areas. If you do need to visit affected areas, you should ensure that your inoculations are up to date and be particularly careful to drink only bottled or purified water as local water sources may be contaminated. There is also a particular danger from contaminated seafood.