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Discussion

Risk of Occupational Exposure to Hepatitis B Virus (HBV)

Hepatitis B virus (HBV) is very efficiently transmitted in the setting of a percutaneous injury that involves an instrument coated with or containing HBV-infected blood. The risk of acquiring HBV from a needlestick injury ranges from 1% to 6% (source patient HBsAg-positive, HBeAg-negative) to 22% to 40% (source patient HBsAg-positive, HBeAg-positive)[1]. The risk of hepatitis C virus (HCV) and HIV transmission with a comparable exposure is much lower: 3% to10% and 0.2% to 0.5%, respectively (Figure 1)[2]. Acquisition of HBV virus can also occur via contact of mucous membranes or non-intact skin with infectious blood or body fluid. The risk of non-percutaneous exposure has not been well quantified, but it may account for a significant proportion of HBV transmission in the healthcare setting. Indeed, many healthcare workers infected with HBV cannot recall an overt needlestick injury, but can remember caring for a patient with hepatitis B[3]. Hepatitis B virus is a hardy virus that can survive in dried blood for up to a week and thus may be transmitted via discarded needles or fomites, even days after initial contamination. Although some experts have suggested that occupational HBV transmission could occur via exposure to bloody body fluids, saliva, semen, or vaginal fluid, to the best of our knowledge, occupational transmission of HBV from these exposures has not yet been documented. Available data would suggest that transmission is unlikely to occur through contact with urine or feces[2].

Epidemiology of Hepatitis B in Healthcare Workers

Epidemiologic studies in the United States in the 1970's demonstrated that healthcare workers (HCWs) had a seroprevalence rate of HBV infection that was 5 to 10 times higher than the general population[1]. Clinicians with direct patient contact, such as physicians, dentists, nurses, and dialysis workers, are at higher risk of acquiring HBV. Laboratory workers and cleaning staff also have higher than average rates of exposure to HBV. In 1983, the HBV vaccine became available in the United States, and in 1991, OSHA required health care facilities to offer free HBV vaccination to any employee at risk for exposure. Between 1983 and 1995, the incidence of HBV infection in United States healthcare workers decreased by a striking 95% percent[4], likely as a result of the increased use of HBV vaccine among health care workers in the latter part of this period. Unfortunately, a significant proportion of United States HCWs do not receive HBV immunization, and remain susceptible to HBV infection. In one relatively recent report, approximately 45% of eligible employees declined HBV vaccination, a figure similar to previous studies[6,7]. The vaccine refusal rate was lowest in groups at higher risk of exposure to HBV, but even among nurses, nearly 30% chose to forego vaccination[5]. In addition, 5-10% of employees who undergo the initial vaccination series may have an inadequate hepatitis B antibody response (defined as serum antibody titers less than 10 mIU/ml)[8]. Thus, systematic availability of HBV postexposure prophylaxis procedures remains critical in order to reduce the risk of occupational HBV infection in susceptible HCWs.

Hepatitis B Immunoglobulin (HBIG) for Postexposure Prophylaxis

Hepatitis B immune globulin (HBIG) is an important component of hepatitis B postexposure prophylaxis. An adequate dose of HBIG provides immediate adoptive neutralizing antibody directed against HBV. In most instances, HBIG is intended to serve as a bridge in the control of HBV until the innate immune system can mount an adequate response. Hepatitis B immune globulin is prepared from human serum known to contain anti-hepatitis B antibodies. In the United States, HBIG contains a minimum of 217 IU/ml of anti-HBsAg antibodies[2]. Donated sera are screened and processed to eliminate virtually any potential transfer of infectious HIV, HBV, or HCV. The recommended dose for HBIG is 0.06 ml/kg given by intramuscular injection. Hepatitis B immune globulinIt may be given concurrently with the hepatitis B vaccine, but should be given at a different anatomic site, such as the gluteal muscles or opposite deltoid muscle[3]. Serum anti-HBs levels typically peak 1 week after injection, and the mean half-life of HBIG is 22 days[2]. In the absence of concomitant administration of giving HBV vaccine, multiple doses of HBIG provide an estimated 75% protection from acquiring HBV in the occupational exposure setting[3]. Adverse reactions to HBIG are unusual but can include pain at the injection site and allergic reactions (urticaria, angioedema, and rarely anaphylaxis). A history of anaphylaxis to any immune globulin (IG) preparation is a contraindication to receiving HBIG. The use of HBIG is considered safe for women who are pregnant or lactating.

Hepatitis B Vaccine and Postexposure Prophylaxis

HBV vaccine is used in the postexposure prophylaxis setting to augment the immune response to hepatitis B. Two HBV vaccines are approved for use in adults; both require administration of three separate injections into the deltoid muscle (Figure 2). In addition, if the HCW has an additional indication for receiving hepatitis A vaccine, they can receive the combination HAV and HBV vaccine. The efficacy of the combination of HBIG and HBV vaccine in reducing the rate of HBV infection acquired through occupational exposure has not been demonstrated directly, but its advantage is inferred because the combined regimen demonstrated an 85-95% efficacy in preventing perinatal transmission of HBV[3].

Evaluation and Management of Occupational Exposure to HBV

In 2001, the United States Public Health Service (USPHS) published guidelines for the evaluation and potential use of postexposure prophylaxis following occupational exposures to HBV, HCV and HIV[3]. These guidelines emphasize that all healthcare facilities in the United States should have specific protocols for HCWs who have potential for exposure to patient bodily fluids. Immediately after the exposure occurs, the HCW should thoroughly wash the exposure site with soap and water. Next, the employee should promptly undergo an evaluation that includes recording of details of the exposure (time, date, type, and site), known information on the source patient (HIV, HBV, and HCV status), and the employee's relevant health history (including hepatitis B immunization status and post-immunization titer). If the source patient can be identified, they should undergo testing for HBV, HCV, and HIV, unless these results are already known. Multiple factors should be taken into account to determine whether postexposure prophylaxis for HBV is warranted (Figure 3)[3]. If the exposure is deemed to confer a significant risk for HBV transmission, the USPHS guidelines recommend prompt initiation of postexposure prophylaxis[3]. As outlined in detail below, the specific type of postexposure prophylaxis is based on the HCW's prior receipt of HBV vaccine and their immune response to the vaccine[3].

The utility of initiating postexposure prophylaxis more than 7 days from the exposure is unclear. If the exposure occurred more than 7 days prior, the hepatitis B vaccine should be given (if indicated), but use of HBIG should be considered on a case-by-case basis, ideally with expert consultation. Similarly, for instances in which the source patient is unidentifiable, such as a needlestick injury involving a needle in a sharps container or from bed linens, the decision whether to provide HBV postexposure prophylaxis should be made on a case-by-case basis, and may require expert consultation, particularly for decisions that involve giving HBIG.

HCW Not Previously Vaccinated

If a HCW has neither a history of receiving hepatitis B vaccine nor of prior HBV infection, they should be presumed to be at significant risk of acquiring HBV infection following an exposure. In this situation, HBIG is indicated if the source of the exposure is HBsAg positive or the hepatitis B status of the source is unknown, but they belong to a high-risk group (men who have sex with men, injection-drug use, prior residence in a HBV-endemic region). The HBIG (0.06 mL/kg IM) should be administered to the HCW within one week of the exposure, preferably within 24 hours (Figure 4). The HCW should also receive the first dose of the HBV vaccine series, ideally concurrently[3]. In instances in which the source patient is unidentifiable, such as a needlestick injury involving a needle in a sharps container or from bed linens, the indication for HBV postexposure prophylaxis should be made on a case by case basis, preferably with expert consultation.

HCW Previously Vaccinated with Effective Response to Vaccine

If an exposed employee was vaccinated for HBV and had a documented post-vaccination anti-HBs antibody titer greater than 10m IU/ml, they would not need postexposure prophylaxis for hepatitis B. In many individuals, serum levels of anti-HBs decline slowly after vaccination[9], but it is unclear whether a remotely vaccinated employee needs a booster for hepatitis B after an exposure. It is reasonable to consider a booster vaccination if the healthcare worker was vaccinated more than 10 to 20 years prior to the exposure, particularly if the exposure was relatively high risk (hollow-bore needle and a HBeAg-positive source patient).

HCW Previously Vaccinated with Lack of Response to Vaccine

Individuals who did not respond to previous attempts at HBV immunization (post-vaccine titers less than 10 mIU/ml) pose a special challenge, since they may not derive benefit from HBV vaccine given in the postexposure setting. In this case, two options are acceptable: (1) administer a single dose of HBIG at the time of exposure and repeat the hepatitis B vaccine series, or (2) administer a dose of HBIG at the time of exposure and repeat a second dose of HBIG one month later[3]. For those employees who have previously failed to respond to two vaccine series, most experts would recommend the latter approach, with the assumption that an additional HBV vaccine series would not generate a significant immune response.

HCW Previously Vaccinated with Unknown Response to Vaccine

If the exposed employee's post-vaccination titer is unknown, anti-HBs titers should be measured. Again, HCWs whose anti-HBs titers demonstrate levels greater than 10 mIU/ml do not need postexposure prophylaxis. Employees whose antibody titers are less than 10 mIU/ml are treated similarly to non-responders (Figure 4). If the turnaround time for titer results is more than 48-72 hours or if the employee has multiple risk factors for poor vaccine response (greater than 50, smoking, obesity, renal failure or immunosuppression), then postexposure prophylaxis with HBIG and the hepatitis B vaccine can be initiated pending lab results.

Use of Antivirals or Interferon for Postexposure Prophylaxis

Although antiviral medications have been successfully used for HIV postexposure prophylaxis, and lamivudine (Epivir) has recently been used to reduce HBV transmission after liver transplantation, data are insufficient to recommend the use of antiviral postexposure prophylaxis for HBV in the occupational setting. Similarly, although use of an interferon-based product would have theoretical benefit, no data exist to support its use in this setting. The 2001 USPHS guidelines for management of occupational exposure to HBV do not recommend the use of antivirals or any interferon-based product for postexposure prophylaxis.

Follow-up and Monitoring of Health Care Worker

Post-vaccination titers should be obtained on all HCWs who received the HBV vaccine. For those who receive HBIG, it is important to wait 4 to 6 months after HBIG administration before anti-HBs titers are drawn in order to accurately assess the HCW's immune response to HBV vaccine (as opposed to detecting remnant antibodies from the administered HBIG). Although no guidelines exist regarding follow-up of HCWs for HBV seroconversion, we would recommend follow-up serology testing (measurement of HBsAg and anti-HBc) at 3 and 6 months after the exposure.