21 percent is the number the Red Cross gave when I took first aid training. In fact I look for tattoos when deciding on what to do with an injuried person.
"A new study shows the risk of contracting hepatitis C increases significantly among people who have tattoos. Researchers from UT Southwestern Medical Center in Dallas studied more than 600 patients. The patients were from the orthopedic spinal clinic, a setting that provided a large volume of patients seeing a physician for reasons unrelated to blood-borne infection. Participants unaware of their hepatitis status were examined, interviewed for risk factors and tested for hepatitis C. They found 18% of these patients had a tattoo. Of those patients with a tattoo, Men Talk more than 20% were infected with hepatitis C and 33% of those patients had acquired their tattoos in a commercial tattoo parlor. Few of the tattoo-associated infections could be traced to injection-drug use, transfusions or other known routes of exposure. Only 3.5% of patients with no tattoos had hepatitis C.