In many parts of the world, intravenous (IV) drug use (shooting drugs into a vein using a needle) is a major risk factor for Hepatitis C (meaning that it makes people more likely to get the disease). One study that looked at 77 countries showed that in 25 of these countries (including the United States), between 60% and 80% (or 6 to 8 out of every 10) of all IV drug users had Hepatitis C. and China. In twelve of the countries in the study, more than 80% of all IV drug users had Hepatitis C. Across the world, as many as ten million IV drug users are thought to have Hepatitis C; the highest totals are in China (1.6 million), the United States (1.5 million), and Russia (1.3 million). Studies have also shown that in places where there are high numbers of IV drug users, people are more likely to have Hepatitis C. For example, prisoners in the United States are ten to twenty times more likely than the general population (people in general) to have Hepatitis C. This is thought to be because prisoners are more likely to things that put them at high risk for getting Hepatitis C, like using IV drugs and getting tattoos with tools that have not been cleaned properly.