Bulgaria poses no health risks in particular for a traveller, as long as you take care. Don’t eat or drink anything that could be contaminated- such as raw vegetables, mayonnaise, or seafood that may not be fresh. If you’re visiting the country in the winter, go well equipped with woollens: winters can be extremely severe in Bulgaria, and hypothermia can result because of exposure to cold.
Medical facilities in Bulgaria are quite good, so even if you should fall ill, you needn’t worry. Many private practitioners and clinics will probably expect you to pay cash, but both first aid as well as emergency consultations is generally free.
Recent economic crises in Bulgaria have caused social turmoil and a rising crime rate is one of the consequences. Although foreigners are not specifically targeted, you shouldn’t take risks. Always keep your hotel room- and your bags- locked, and be particularly careful not to exhibit your wealth- flashing large amounts of cash literally invites robbery. Keep an eye on your valuables, and a firm grip on your wallet, especially in a crowded area. Try to get back to your room before dark, and don’t wander around deserted areas after sunset.