High Risk Groups - United States
Many of the high risk groups for hepatitis C are easily identified, due to practices resulting in frequent exposures to blood or risk factors for transmission.
Blood transfusions currently seem to account for only approximately 5-10% of all cases of hepatitis C. Prior to 1990, there were no tests for hepatitis C against the blood supply, and the rate of post-transfusion hepatitis was between 8% and 10%. Anyone who received a blood transfusion prior to that time is at risk for having been infected. Incidence among hemophiliacs, who receive frequent transfusions of blood and blood products, is particularly high, ranging between 25-40%. Women who have had Cesearean sections prior to 1990 represent another significant risk group, as these operations were frequently accompanied by blood transfusion.
Blood tests have greatly reduced the rate of post-transfusion hepatitis C - CDC estimates the risk factor for transfusion-contracted HCV during the 1990-1993 period at 5%, and risk of infection was brought down to less than 1% after 1993. Today, the risk of post-transfusion infection is negligible, at approximately 1 per 100,000 units of blood. Blood banks also now also notify donors if they detect the virus.
IV drug users represent the largest single risk group. Hepatitis C infection among intravenous drug users occurs at an alarming rate. As with HIV, the sharing of contaminated needles and syringes increases the chance of infection dramatically: incidence of HCV antibody rates among I.V. drug users has surpassed 50 percent in many studies and almost reached 100 percent in others. Within only six months to a year after beginning intravenous drug use, 50-80 percent of drug users test positive for the hepatitis C antibody. I.V. drug users account for about 30-40% of all identified cases, and about 50 percent of all new cases of the disease.
Sexual contact has been clearly identified as a means of transmitting hepatitis C. Several studies of risk factors in sexual activity found rates of infection between 1 and 18% for homosexually active individuals, 1 to 10% among heterosexually active individuals, and 1 to 12% among female prostitutes, with the primary risk factors for infection being greater numbers of partners, unprotected sex, simultaneous infection with other STD's, and traumatic sexual activity. Seroprevalence for long term partners of hepatitis C patients was found to be around 5%.
Household contact with another household member that has hepatitis
C has also been strongly implicated, and this, in combination with heterosexual exposure, is believed to be responsible for approximately 13% of all infections. The incidence of household-member transmission cases has more than doubled since 1990. Maternal-infant transmission has also been documented as a mode of spread, occuring in no more than six percent of children of hepatitis C positive mothers.
Around 2% of all cases of hepatitis C are thought to be contracted through the occupational risk (needle-stick injuries, blood spills, etc) involved with the health care profession.
Prisoners have enormous incidence of infection - rates reported in some California prisons exceed 80%, with certain institutions reporting nearly 100% of their prisoners infected.
Some skin piercing practices, notably tattooing, body piercing, and acupuncture, have contributed significantly to the spread of HCV, particularly in less industrialized nations. Tattooing in particular poses a serious risk. Even in the presence of good sterilization, studies have suggested that the ink used in tattooing can become contaminated and transmit the virus.
Several studies have shown that adequate blood can be present in other body secretions to transmit infection. Cocaine users have an abnormally high risk of infection due to the fact that they frequently share snorting straws, which may have small amounts of blood-carrying mucous on them. Such indirect sources of blood may explain many cases of inter-household transmission.
Less obvious, specialized risk factors have been identified resulting from indirect exposures to blood - including manicures, shared toothbrushes and razors, and straight razors in barber shops.
Particular racial, ethnic, and income groups are at higher risk of infection. An ethnic analysis in one earlier, somewhat underestimated study
(1994) determined that Caucasian Americans statistically accounted for the most number of infected persons, while the highest incidence rates
were among African and Hispanic Americans. The highest prevalence of the disease was found in middle-aged people (30 to 49 years old) who accounted for 3% -4% of the cases. Prevalence among black men in this age group approached 9% to 10%. Gender, however, did not emerge as a significant risk factor in the population as a whole. In the United States, blacks have the highest incidence rates, followed by Native Americans, Hispanics, and whites.
Similarly, low income groups seem to have the highest risk of infection. In one study at the inner city VA Hospital in Washington, D.C., one in five people admitted tested positive for HCV. Similar results (18%) were obtained at the John Hopkins University Hospital, located in Baltimore's inner city.
The higher incidence among certain racial, ethnic, and income groups is probably the result of higher rates of other cofactors, but may also be the result of unidentified modes of transmission. Many groups showing high incidence of infection do not have obvious correlations with known modes of transmission, pointing towards the existence of unknown routes of transmission. For example, there is a serious question as to why many alcoholics are infected with HCV. In many surveys, about a third of people who are alcoholics are also infected with the HCV virus. Whether alcoholics are in fact more prone to infection has not been firmly established.