The true prevalence of HCV in the incarcerated population is difficult to obtain as no mandated screening programmes exist and the number of studies that investigated HCV prevalence in this population is limited. Of these studies, the prevalence of HCV ranged from 23.1 to 39.4% (6–12) (Table 1). The most recent data from California correctional system were a cross-sectional study of 469 prisoners from three California State correctional facilities in 2005, which showed a prevalence of 34.3% (6). In an older, but much larger study also set in California, 4513 inmates in six correctional facilities, the overall prevalence was 41.2% (10). Similarly, in a study of 4269 prisoners in Rhode Island, 23.1% of prisoners were HCV antibody positive (8). Another large study from the Maryland correctional system yielded an HCV prevalence of 29.7% (12). In 2004, the Bureau of Justice Statistics published the results of a survey of 1209 of 1584 State public and private correctional facilities nationwide (76% participation). Of 57 018 HCV tests administered, 17 911 were positive (31%) (13). There were no additional data from individual States' Department of Corrections that were identified.
Table 1. Prevalence of hepatitis C virus in USA prison population
|Reference||Year published||Location||Study design||Number of subjects||Number of HCV positive (%)|
|Fox et al. (6)||2005||California||Cross sectional||467||160 (34.3)|
|Solomon et al. (7)||2004||Maryland||Cross sectional||3661||1089 (29.7)|
|Macalino et al. (8)||2004||Rhode Island||Prospective cohort||4264||983 (23.1)|
|Baillargeon et al. (9)||2003||Texas||Cross sectional||2144||593 (27.7)|
|Ruiz et al. (10)||1999||California||Cross sectional||4513||1859 (41.2)|
|Spaulding et al. (11)||1999||Colorado||Cross sectional||1224||367 (30.0)|
|Vlahov et al. (12)||1993||Maryland||Prospective cohort||265||100 (38.0)|
Despite differences in the time of study and region of USA, the prevalence of HCV is relatively uniform among these studies of incarcerated populations. Noticeably missing from these data are seroprevalence studies from other states; hence, any extrapolation from this relatively small dataset would be an estimate. In one study by Spaulding et al. (11), a survey was sent to the Department of Corrections for each of the 50 states plus the District of Columbia regarding HCV statistics in their respective prisons. Of the states polled, 36 states and the District of Columbia responded. Of the states that did respond, only California reported a formal seroprevalence study (10), but otherwise stated that prisoners were not routinely screened for HCV. Colorado was the only state that reported routine HCV screening of prisoners and found a prevalence of 30%. Other states that responded to the survey did not report routine screening and not surprisingly reported a wide range of HCV prevalences ranging from 5 to 83%. It is unclear when prisoners who underwent non-routine screening were tested for HCV and this was not defined by any of the states. But as this was non-routine screening, these results are difficult to interpret in this setting and are inherently biased.
A homeless person, as defined by the US Department of Housing and Urban Development, is not only an individual who does not have a night-time residence, but can also reside in a homeless shelter, or temporary housing (including welfare hotels, congregate shelters and transitional housing) (14). In studies involving homeless persons, the prevalence of HCV was found to range from 19 to 69.1% (15–23)(Table 2). Two studies that involved homeless veterans found prevalences of 41 and 44% (19,21).
Homeless persons infected with HIV at baseline had the highest prevalences of HCV (65 and 69.1%) (16, 17). Further, in the study where 69.1% prevalence was found, the prevalence increased to 73.1% by the end of the median follow-up period of 39.7 months (17). In their subset of HIV-positive veterans, Cheung et al. (21) found that 72.7% were found to be HCV positive. As there are shared routes of transmission, HIV as a risk factor for HCV in the homeless population is biologically plausible (24). Studies have shown that HCV is increased in HIV-positive persons (25–27) and those who are homeless (22, 23), but there is a paucity of data correlating HIV co-infection as a risk factor for HCV in the homeless population. These data strongly suggest, however, that HIV-positive homeless persons are at a particularly high risk for HCV infection. However, as HIV-positive homeless people are not representative of homeless population in general, prevalence data from these studies will not be used to calculate the prevalence of HCV in the homeless population as this would lead to overestimation.
The lowest HCV prevalence in a homeless population was found by Schwarz et al. (15) to be 19% among homeless caregivers. A caregiver was defined as a person who functioned as a parent (not necessarily biological) to a child aged 2–18 years. All of the caregivers identified for the study lived in homeless shelters or transitional housing in Baltimore, MD. While this prevalence found is elevated from the general population reported in the NHANES study (4), it is significantly lower than the aforementioned homeless populations. It may be that persons acting as caregivers may be less likely to engage in high-risk activities that would predispose them to HCV, leading to lower rates of infection.
Injection drug users
Injection drug use is now considered the primary cause of HCV in USA today (28). The prevalence of HCV among injectable drug users ranged from 27 to 93% (29–40). This wide range reported in the literature is partially explained by variations in the duration of IDU among subjects. A recent study by Tseng et al. (36) showed HCV prevalences of 66.2, 87.6, 97.6 and 98.7% for drug usage durations of <9, 10–19, 20–29 and>30 years respectively (P<0.0001). Younger age groups also had significantly lower incidences of HCV than older age groups (P<0.0001), although age is likely a surrogate for duration of IDU. Indeed, the studies that showed <40% prevalence of HCV only included patients younger than 30 years of age (30, 32, 35). On the opposite end of the spectrum was a large multicity trial (Seattle, Detroit, Newark, San Francisco, Denver and Baltimore) that included patients up to 45 years of age, but not specific data on duration of use, and had the highest rates of HCV prevalence (69–93%) (34).
Perhaps the greatest contribution to decreased HCV prevalence among injection drug users is outreach and harm reduction programmes implemented nationwide. The Drug User Interventional Trial (DUIT) is a national trial that took place in major cities across USA (Balitmore, Chicago, Los Angeles, New York and Seattle). It is described as a ‘small group, cognitive behavioural, peer education intervention designed to reduce injection and sexual risk behaviours for HIV and HCV in young injection drug users’ (41). The DUIT observed a 29% decline in overall injection risk and sexual risk behaviours (42). Needle exchange programs have reported similar success in reducing new cases of HCV (36, 39, 43, 44) and increasing access to sterile syringes would likely decrease transmission of HCV as well (45). Thus, a major contributor to the lower HCV prevalences seen in the aforementioned studies has been outreach and harm reduction programmes targeted at this very high-risk population.
The largest study involving injection drug users in USA is the Collaborative Injection Drug User Study (CIDUS), which collected data from 1994 to 1996 (CIDUS I), 1997 to 1999 (CIDUS II) and 2002 to 2004 (CIDUS III/Drug User Intervention Trial) (31). CIDUS collected information from four sites: Baltimore, Chicago, Los Angeles and New York and showed HCV prevalences of 65, 35 and 35% during CIDUS I, II and III respectively. Thus, there appears to be a large decrease in HCV prevalence nationwide among injection drug users over the years, but it is important to realize that the demographics of the study population across the three studies has changed dramatically over time as well. In CIDUS I, the majority were drug users aged 31–40 years old and 44.7% used injection drugs for>10 years. During CIDUS II and III, however, injection drug users were never older than 30 years and only 5.8 and 8.0% used injection drugs for>10 years. Because of this, the CIDUS studies should not be considered a representative sample as older injection drug users were not included in their final analysis.
Emerging evidence suggests that non-injection drug use (NIDU) is also considered a risk factor for the transmission of HCV. Transmission likely requires exposure to HCV RNA in biological fluids and disruptions in mucous membranes that allow the virus to enter the bloodstream (46). Besides blood, HCV RNA has also been detected in the saliva and gingival crevicular fluid of persons with chronic HCV (47, 48). Nasal secretions of intranasal drug users have also been shown to harbour HCV (49). Thus, sharing of drug paraphernalia contaminated with HCV RNA appears to facilitate the transmission of the virus.
A recent systematic review by Scheinmann et al. (50) showed that HCV prevalence was increased in non-injection drug users compared with the general population. Among the identified studies, 12 had American source populations, with HCV prevalences ranging from 3.9 to 31.8%. Importance weaknesses to his body of literature, however, must be noted. Nine of the 12 American studies identified in the systematic review were based in New York and may not reflect NIDU usage patterns in other parts of the nation. Also, in many of these studies, NIDU was a secondary outcome to IDU and may be subject to investigator confounding. Further, many of the studies may have been subject to misclassification bias and may not have controlled for drug-related confounders. The authors concluded that studies investigating the relationship between HCV and NIDU are in their early stages and more rigorous studies still need to be performed.
The NHANES study found an HCV prevalence of 57.5% among patients who reported the use of injectable drugs during their lifetime, but did not collect information regarding the duration of drug use or any other demographical information specific to injectable drug users (4). Still, the estimated prevalence by the NHANES appears to be a good estimation of the true HCV prevalence among injection drug users as it falls within the range of the aforementioned studies available in the literature.
The NHANES also collected data coded as ‘no drug use or only marijuana’ (0.7% HCV prevalence) and ‘other drug use (except marijuana) (3.5% HCV prevalence)’. By this classification, NIDU would fall into the latter category. Although the quality of studies investigating the relationship between NIDU and HCV has been called into question, the NHANES result appears to be a reasonable estimate as it nearly equals the most conservative HCV prevalence among non-injection drug users found in the literature.
Most HCV transmission to HCW is because of direct percutaneous exposure to blood contaminated with HCV (24). The overall prevalence of HCV infection in HCWs appears to be similar to the general population estimated by NHANES, ranging from 0.7 to 3.2% (51–63) (Table 3). The definition of HCW is broad and seroprevalence studies have generally involved physicians, surgeons, firefighters, paramedics and emergency medical technicians. In seroprevalence studies of medical doctors (specifically surgeons and dentists), the prevalence was found to be 0.9–1.8% (59–63). The vast majority of other seroprevalence studies, however, involve firefighters, emergency medical technicians and paramedics.
Table 3. Prevalence of hepatitis C virus in USA healthcare workers
|Reference||Year published||Location||Study design||HCW studied||Number of subjects||Number of HCV positive (%)|
|Gershon et al. (51)||2007||Rhode Island, Texas, Maryland||Cross sectional||C||310||7 (2.3)|
|Datta et al. (52)||2003||Georgia||Crosssectional||F||437||9 (2.1)|
|Datta et al. (52)||2003||Connecticut||Cross sectional||C, E, F, P||382||5 (1.3)|
|Datta et al. (52)||2003||Pennsylvania||Cross sectional||F||2127||77 (3.6)|
|Rischetti et al. (54)||2002||Oregon||Cross sectional||C, F, P||719||7 (1.0)|
|Roome et al. (55)||2000||Florida||Cross sectional||E, F||3362||70 (2.1)|
|Peate et al. (56)||2001||Arizona||Prospective cohort||E||477||9 (1.9)|
|Upfal et al. (57)||2001||Michigan||Cross sectional||E, F, P||2447||28 (1.1)|
|Werman and Gwinn (58)||1997||Ohio||Prospective cohort||E||107||1 (0.9)|
|Thomas et al. (59)||1996||Maryland||Cross sectional||D, S||648||9 (1.4)|
|Panlilio et al. (60)||1995||Georgia||Cross sectional||S||770||7 (0.9)|
|Gerberding (61)||1994||California||Prospective cohort||M, O||815||12 (1.4)|
|Polish et al. (62)||1993||California||Retrospective cohort||M, O||1677||23 (1.4)|
|Klein et al. (63)||1991||New York||Case–control||D||456||8 (1.8)|
Veterans (non-active military personnel)
Two recent nationwide studies have suggested that veterans are at an increased risk for HCV infection. A study by Dominitz et al. (64) used a two-stage cluster sample to randomly select 3863 users of the veterans affairs (VA) medical services nationwide. Of these, 1288 veterans responded and the researchers found an overall prevalence of 5.4% after correcting for sociodemographical factors. The authors found that veterans had a higher prevalence because of excess exposure to traditional risk factors (blood transfusions and IDU) compared with the general population. A similar nationwide study of 26 102 veterans undergoing phlebotomy nationwide on National Hepatitis C Surveillance Day showed a prevalence of 6.6% (65).
Conversely, the NHANES study found an overall prevalence of 2.8% (95% confidence interval 1.9–4.2%) and appears to have underestimated the prevalence of HCV in veterans (4). The prevalence of HCV among veterans has been reported to be 5.4–41.7% in large studies over the past decade (19, 21, 64–76) (Table 4). The range of HCV prevalences reported is wide and reflects the varying populations of veterans who reside in USA. The highest prevalences of HCV came from studies involving homeless veterans (19, 21). Other subpopulations of high-risk veterans studied include those with HIV and mental illnesses who also appear to be at an increased risk. Conversely, a study by Seeff et al. (77) of young health military recruits in a university setting reported a prevalence lower than the general population, highlighting the importance of veterans' lifetime exposure to risk factors and the development of HCV infection.
Table 4. Prevalence of hepatitis C virus in USA veterans over the past decade
|Reference||Year published||Population||Study design||Number of subjects||Number of HCV positive (%)|
|Himelhoch et al. (67)*||2009||Veterans with schizophrenia or bipolar||Cross sectional||223 137||13 352 (6.0)|
|Groom et al. (68)||2008||Minnesota VA outpatients||Retrospective cohort||12 485||681 (5.4)|
|Kilbourne et al. (69)*||2008||Veterans with schizophrenia, bipolar or depression||Retrospective cohort||18 056||1250 (6.9)|
|Mallette et al. (70)||2008||Rhode Island VA with one traditional risk factor†||Cross sectional||5646||412 (7.3)|
|Dominitz et al. (64)||2005||Randomized national sample||Cross sectional||1288||52 (5.4)‡|
|Matthews et al. (71)*||2008||Veterans with substance abuse and bipolar disorder||Retrospective cohort||130 021||13 531 (10.4)|
|Goulet et al. (72)*||2005||HIV-positive veterans||Case–control||25 116||4489 (17.8)|
|Desai et al. (19)*||2003||Homeless veterans||Cross sectional||418||184 (44.0)|
|Mishra et al. (73)||2003||Florida and Georgia outpatients||Cross sectional||274||27 (9.9)|
|Brau et al. (74)||2002||New York VA in/outpatients||Cross sectional||1098||116 (10.7)|
|Cheung et al. (21)*||2002||Homeless veterans||Retrospective cohort||597||249 (41.7)|
|Roselle et al. (65)||2002||Phlebotomy in/outpatients on 1 day nationwide||Cross sectional||26 102||1724 (6.6)|
|Briggs et al. (75)*||2001||Urban California VA||Cross sectional||1032||185 (17.7)|
|Austin et al. (76)||2000||Georgia VA inpatients||Cross sectional||530||56 (10.6)|
|Cheung (66)*||2000||VA in/outpatients including psychiatric disease||Cross sectional||8558||2985 (34.8)|
Recipients of chronic haemodialysis
Patients on chronic haemodialysis are at increased risk for HCV infection and it appears to be related to time that the patient has been receiving dialysis as well as the number of blood transfusions received (78). Blood transfusions received before second-generation HCV screening assays in 1992 is considered an independent risk factor for HCV transmission (79), but has not, to our knowledge, been specifically studied in the haemodialysis population.
Hepatitis C virus outbreak investigations at dialysis centres have revealed multiple opportunities for cross contamination between infected and non-infected patients including using receiving dialysis immediately after an infected patient, dialysis equipment that is improperly sterilized, use of common medical carts with contaminated surfaces and sharing of multiple dose medication vials and priming buckets (78).
The most recent national surveillance study on dialysis-associated diseases was published in 2002 and represents the most current infection control statistics from dialysis centres nationwide (80). In conjunction with the Centers for Medicare and Medicaid Services (CMS), the Center for Disease Control (CDC) sent out surveys to all 4185 haemodialysis centres licensed by the CMS in USA, with a 96% response rate. The overall prevalence of HCV in this national study was 7.8%, which is decreased from 1995 (10.4%). The authors attributed this decrease, in part, to increased awareness on HCV transmission.
Patients with haemophilia are blood transfusion dependent and are at an increased risk for HCV infection. Specifically, those who received blood transfusions before 1987, when heat inactivation of factor concentrates dramatically improved blood safety relative to HCV and other viral agents, have been reported to have high prevalences of HCV: 76.3, 98 and 100% (81–83). The advent of the second-generation HCV screening assay in 1992 has nearly eliminated the transmission of HCV through blood transfusion. The risk is not zero, however, as mathematical modelling has suggested that transfused blood may still transmit HCV in 1:100 000 to 1:200 000 recipients (79). The estimated prevalence of haemophiliacs who have received transfusions and other blood products before the screening era is <0.01% of the US population today (28).
Nursing home residents and hospitalized patients
Nursing home residents would also not have been sampled by the NHANES because only non-institutionalized persons were included. There is only one study that measured the prevalence of HCV in the nursing home population. Chien et al. (85) found that 4.5% of residents at three nursing homes in the greater St Louis area were anti-HCV positive. It would be unwise to draw certain conclusions regarding HCV in the nursing home population but it would appear that they are at an increased risk.
Patients hospitalized during the NHANES study would have been missed by the survey. We found seven studies that measured the prevalence of HCV in hospitalized patients, with prevalence ranging from 4 to 20.3% (66, 76, 86–90) (Table 5). Of these, three involved patients in emergency rooms (ERs) (87–89), two collected data from inpatients at VA hospitals (66, 76), one collected data from a large psychiatric hospital (90) and one collected data from inpatients and outpatients in a university hospital (86).
Table 5. Prevalence of hepatitis C virus in hospitalized patients
|Reference||Year published||Population||Study design||Number of subjects||Number of HCV positive (%)|
|Hall et al. (89)||2010||Emergency room||Cross sectional||404||16 (4.0)|
|Meyer (90)||2003||Psychiatric inpatients||Retrospective cohort||535||109 (20.3)|
|Brillman et al. (88)||2002||Emergency room||Cross sectional||223||38 (17.0)|
|Austin et al. (76)||2000||Veteran inpatients only||Cross sectional||530||62 (11.7)|
|Cheung (66)||2000||Veteran in/outpatients||Cross sectional||8558||2985 (34.8)|
|Lanphear et al. (86)||1994||In/outpatients||Prospective cohort||1387||176 (12.7)|
|Kelen et al. (87)||1992||Emergency room||Cross sectional||2523||454 (18.0)|