Theft of, and from, cars is common. Do not wear jewellery or carry large amounts of cash. Avoid street money changers. Take a photocopy of your passport and your airline tickets which can be difficult to replace it stolen. Keep these copies separate together with the numbers of travellers cheques and credit cards.
Dengue fever is a cause for concern.
There have been many confirmed cases in the areas of Puntarenas and Guanacaste on the Pacific coast, and Limon on the Atlantic coast. Deaths from secondary infections have occured. Special care should be taken when swimming from all beaches in Costa Rica especially on the Atlantic coast. Rip tides are very common. Seek reliable local advice.