Exposure to blood-borne pathogens, including hepatitis C virus (HCV), presents a serious risk to health care workers (HCWs). There are various current estimates of HCW numbers throughout the world: the World Health Organization (WHO) cites a figure of 35 million, a conservative estimate that may be as high as 100 million if we include all health care personnel in addition to doctors, nurses, and midwives in active practice. It is clear that the potential number of people at risk of exposure is a cause for concern, particularly in under-resourced health care systems. Factors influencing the risk of transmission of blood-borne pathogens between patients and HCWs include the frequency of the types of exposures that enable transmission; the prevalence of blood-borne infection among patients treated by the HCW; the risk of transmission of an infection when exposure to an infected source occurs; and the effectiveness of post-exposure management or treatment. Risk assessment of bloodborne pathogen transmission in the health care setting takes into account information from various sources, including frequency and preventability studies of blood contacts, seroprevalence studies among HCWs, and prospective studies that assess the risk of seroconversion following exposure to infected blood.
In this chapter we will review these factors in relation to HCV transmission.
MAGNITUDE OF THE RISK OF HCV TRANSMISSION IN HEALTH CARE SETTINGS
Generally, HCV is easily transmitted via direct and copious exposure to blood such as during transfusion of blood or blood products. Percutaneous exposures to HCV (e.g. accidental needlestick injuries) have also been documented as a means of HCV transmission.
In the health care setting, HCV transmission occurs mainly via percutaneous or transmucosal exposure to the blood or bodily fluids of infected patients. Occupational exposures include needlestick and other puncture injuries as well as direct inoculation of the virus onto the mucosal surface of the eyes, nose, or mouth through accidental splash. HCV does not spontaneously penetrate intact skin, and airborne transmission of the virus does not occur.
The risk that an HCV-infected individual will transmit the virus may be related to the type and size of the inoculum, the transmission route and the viral titer, but there is insufficient data on the threshold concentration of virus required to transmit infection.
Needlestick injury has proved to be a strong independent predictor of the likelihood of acquiring HCV infection among health care personnel . In 106 hospitals in the United States, the annual reported percutaneous injury incidence rate was 5.3 injuries per 100 persons . Higher rates of injury have been observed in males, in persons under 45 years old, and in persons employed for less than 4 years . Studies published between 1992 and 2002, with data on more than 11,000 HCV-exposed HCWs in 6 countries, indicate that the average rate of HCV transmission following a single needlestick accident is 0.5% . According to SIROH (the Italian study on the occupational risk of acquiring human immunodeficiency virus (HIV) infection), the largest and most standardized study of HIV in the world, there have been 3795 exposures to anti-HCV positive patients and a transmission rate as low as 0.4% . This rate increases to 0.9% for large-sized inoculates (hollow needles full of blood) and decreases to 0.3% for conjunctival exposure. These figures are much lower than those observed for HBV. In fact, the average risk of HBV infection in a HCW after a needlestick injury and in the absence of vaccination or post-exposure prophylaxis is 5% if the source patient is Hepatitis B e antigen (HBeAg)-negative and 19-30% if the patient is HBeAg-positive  (see Table 1). The risk of HCV transmission appears to increase if the source patient is co-infected with HIV, an observation supported by both anecdotal reports and surveillance studies [7,8].
| ||TABLE 1. Average risk of seroconversion following percutaneous to an infected source |
PREVALENCE STUDIES OF HCV INFECTION AMONG HCWs
Seroprevalence studies have shown that the rate of HCV infection among HCWs is no higher than that observed among blood donors [1,9-11]. Interpreting the results of these studies is complex because of all the potentially confounding variables that may influence such studies - such as geographical differences in prevalence, genetics, socioeconomic factors, race, and environmental factors most were not investigated in the studies. Factors that have been associated with increasing HCV prevalence in at least one study include increased seroprevalence of older workers, increased seroprevalence with more years in a health care occupation, a history of blood or blood product transfusion, and a persistent occurrence of needlestick injuries.
An Italian seroprevalence survey of 5813 HCWs has shown a gross overall HCV rate that is only slightly higher than the one observed in Italian blood donors . However, this study inappropriately used blood donors as controls because it was convenient from a data-collection perspective. As a group, blood donors are not the best controls, because individuals who are at risk for blood-borne infection or have a history of hepatitis are, as a rule, specifically excluded from donation. In any case, this study reports only a history of blood transfusion as being significantly associated with HCV infection, suggesting that exposure to the virus in HCWs occurred outside the workplace.
INCIDENCE STUDIES OF HCV INFECTION AMONG HCWs
Although prevalence studies have been reassuring with regard to the risk of occupational transmission of HCV infection to HCWs with potential blood exposure, incidence studies show a different pattern. For the years between 1991 and 2004, the specific surveillance system for acute viral hepatitis in Italy (SEIEVA), reported a higher incidence rate of acute hepatitis C among HCWs than in the general population when controlled for age [13,14] (see Figure 1). The proportion of HCWs with acute hepatitis C who reported needlestick injury was 13.8% between 1991 and 1994 and 14.3% between 1995 and 2004. However, since HCWs are regularly surveyed after an accidental needlestick exposure to detect possible infection, this study may contain the potential for ascertainment bias. The proportion of subjects with jaundice, who are more easily ascertained, was slightly higher in the general population than in HCWs, therefore it might be supposed that the excess number of non-jaundice cases among HCWs was diagnosed through routine testing after accidental exposure. After excluding individuals with asymptomatic acute HCV infection, the excess acute hepatitis C incidence among HCWs still remained unchanged, as an additional proof of the reliability of the findings.
Four other studies have attempted to determine the number of incident HCV infections among cohorts of previously uninfected HCWs [15-18]. Taken together, these studies clearly document some risk for HCV infection, though obviously not of the same magnitude as for hepatitis B virus (HBV), and to some extent higher than for HIV infection. In the United States, a study of 960 dental HCWs over a 2-year monitoring period showed an incidence of HCV infection of 0.15 per 100 person-years . In Italy, only one incident infection occurred among 765 hospital workers over a 6-year period, for an annual rate of 0.02% . In San Francisco, only one new infection was observed in a population of HCWs working at a large hospital, over an 8-year follow-up period, resulting in an incidence density of 0.08 per 100 person-years . Finally, another study from the United States observed that the incidence of clinical non-A, non-B hepatitis among HCWs at university hospitals over a 10-year period was approximately 3 times higher as compared to non-HCWs . However, these latter findings should be interpreted with caution, as the authors compared data from active surveillance with those from passive surveillance in the community. Together, these cohort studies demonstrate a small but measurably increased risk for HCWs to acquire HCV infection as a result of occupational exposure.
| ||Figure 1. Incidence rates (cases x 100,000) of acute hepatitis C among Health Care Workers (■) and the general population (●) in Italy [13,14]. |
POST-EXPOSURE PREVENTION OF HCV INFECTION
The lack of evidence from randomized clinical trials on the efficacy of any medical intervention in preventing chronic infection after percutaneous exposure to HCV has prevented the adoption of specific and universal guidelines. Consequently, many hospitals have adopted their own protocols, and the high level of variability among these is a source of uncertainty as to their true preventive effect.
The administration of immunoglobulins for post-exposure prophylaxis is no longer indicated in HCWs after needlestick injury . Antiviral agents such as pegylated interferon alpha (PEG-IFNα) in association with ribavirin are effective agents in chronic hepatitis C, but their role in preventing the risk of parenteral exposure has not been evaluated in the context of randomized clinical trials and therefore should not be recommended. Since acute hepatitis C can be efficiently cured using PEG-IFNα treatment [20,21] and the rate of spontaneous viral clearance after acute HCV infection is high , one rational and practical strategy is treat only the few subjects who still remain positive for HCV-RNA 3 months after exposure.
We therefore recommend that HCWs with parenteral exposure adopt a watch-and-wait approach, with careful clinical and laboratory evaluation at baseline to exclude pre-existing viral liver disease, and to perform monthly ALT testing up to 6 months post-exposure. Anti-HCV tests and, if these prove to be positive, qualitative HCV-RNA measurements should be performed only in individuals with increased ALT levels.
What are the conclusions that can be drawn from an extensive analysis of the published literature? Certain points are clear: HCV transmission may occur through occupational exposure to blood, even if less efficiently than HBV transmission; the average rate of HCV transmission following a single needlestick accident is 0.5%; the incidence rate of acute hepatitis C is slightly higher than that observed in the general population.
Are HCWs at increased risk for HCV infection? The answer may be yes, but the magnitude of the risk is low.
However, even a small excess risk, when applied to a large population such as HCWs, is cause for concern - particularly in developing countries. Therefore, in the absence of effective immunoprophylaxis measures for HCV, we strongly recommend strict adherence to universally accepted precautions regarding blood and other bodily fluids as well as the correct disposal and handling of sharp objects in hospital settings.
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