If stds are sexually transmitted how can you get them by touching blood that's out in the open, ?

Termanology: The category of "sexually transmitted disease" is just a group of problems that can pass sexually. The germs involved are not limited to that mode of transmission. Hepatitis B can transmit sexually or through a tainted needle, or contact with blood of an infected person.The same goes for AIDS, syphilis and many other diseases. Some are less likely to pass through non sexual means.