Cuba does not present any unusual health risks to travelers. Visitors occasionally may experience travel related illness common to any Caribbean country, including gastric upset. Risk can be minimized by such routine precautions as hand-washing before touching food, drinking only bottled liquids (or purified water), staying well hydrated, and making sure fresh fruits and vegetables have been properly washed.
Some swimmers at Cuban beaches have reported stings from a Portuguese man-of-war, a jellyfish-like creature whose long tentacles and can cause severe reactions in humans when touched. If affected, apply hot water to the area to alleviate the pain, and seek medical assistance immediately.
Cuba has effective HIV control programs, but ultimately each individual is responsible for minimizing his or her chances of exposure to Sexual Transmitted Diseases by taking adequate precautions and practicing safe sex. Condoms may not be as readily available in Cuba as elsewhere, so travelers should bring their own supply as warranted.
Travelers should also bring mosquito repellant, particularly if they plan on significant outdoor activity outside of Havana (e.g. hiking in the countryside).