[Table of Contents]

Volume: 23S3 - May 1997

PREVENTING THE TRANSMISSION OF BLOODBORNE PATHOGENS IN HEALTH CARE AND PUBLIC SERVICE SETTINGS

ll. Epidemiology of the Transmission of Bloodborne Pathogens

The risk of acquiring a bloodborne infection, i.e., HIV, HBV, or HCV in a health care or public service setting depends on three factors⁽⁸³⁾:

• A. Significant exposure to bloodborne pathogens
• B. Prevalence of infection in the population
• C. Risk of infection due to exposure to bloodborne pathogens

A. Significant Exposure to Bloodborne Pathogens

The evaluation of a significant exposure to a bloodborne pathogen requires investigation of two criteria, type of body fluid and type of exposure.

1. Types of body fluids capable of transmitting HIV, HBV, and HCV from an infected individual include

• blood, serum, plasma and all biologic fluids visibly contaminated with blood
• laboratory specimens, samples or cultures that contain concentrated HIV, HBV, HCV
• organ and tissue transplants
• pleural, amniotic, pericardial, peritoneal, synovial and cerebrospinal fluids
• uterine/vaginal secretions or semen (unlikely to be able to transmit HCV)
• saliva (for HCV, HBV, and HIV if a bite is contaminated with blood and for HBV if a bite is not contaminated with blood)

Feces, nasal secretions, sputa, tears, urine and vomitus are not implicated in the transmission of HIV, HBV and HCV unless visibly contaminated with blood. The risk of transmission from screened donated blood and manufactured blood products is negligible in Canada.

2. To be considered significant, the type of exposure is one in which one of the infected fluids listed in II A.1. comes into contact with the HCW's tissues as follows:

• tissue under the skin (e.g., percutaneous or broken skin following a bite)
• non-intact skin (e.g., cut, chapped or abraded skin)
• mucous membrane (e.g., eyes, nose or mouth)

In summary, if the type of body fluid and the type of exposure is indicative of a significant exposure, further investigation is warranted⁽⁵⁾.

Exposure on intact skin does not represent significant exposure.

Significant sources of blood exposure for patients or clients include inadequately cleaned, disinfected or sterilized equipment used in invasive procedures and in hemodialysis units^(1,84-94) and cross-contamination of multi-dose injectable medication vials^(79,95).

Occupational transmission of HIV, HBV and HCV in health care and public service settings is most commonly associated with injuries involving needles or other sharp instruments or implements^(67,96).

Transmission following mucous membrane, i.e., mouth, eyes, or non-intact skin exposures has been reported much less frequently⁽⁶⁷⁾. Airborne transmission of bloodborne pathogens has not been documented^(40,97-102).

The occupational groups that have reported the greatest numbers of occupationally acquired bloodborne infections are nurses, clinical laboratory workers, and physicians⁽¹⁰³⁾ (unpublished data, PHLS AIDS Centre, Communicable Disease Surveillance Centre, London, UK). See Table 2, page 8, in section II C.1.i. for exposure data from the Health Canada National Surveillance of Occupational Exposure to HIV Program. Types of exposure by occupational group are detailed.

In a study conducted in three large hospitals and two small community hospitals in Montreal, in 1992, nurses were by far the most exposed group, incurring 75% of the reported exposures. Nearly three quarters of total exposures were needle stick injuries. The majority of exposures occurred on medical and surgical wards, followed by the operating and emergency rooms, intensive care units and clinical laboratories⁽¹⁰⁴⁾.

In a study of a random sample of registered nurses in Alberta during 1992, 50% of the 326 nurses surveyed reported one or more needle stick injuries in the previous year. These 326 nurses sustained 630 injuries or, on average, approximately two injuries per nurse per year⁽¹⁰⁵⁾.

In a study carried out in all 34 centres locaux de services communautaires (CLSCs - local community services centres) in Montreal in 1993, nurses reported 80% of the exposures and nurses sustained 22 out of the 24 reported needle stick injuries. The distribution of exposures by location showed that almost a third (32%) occurred at the patient's house, followed by the vaccination room (21%), and the veni-puncture centre (15%). School, emergency room and clinical laboratory were the three other locations most often reported⁽¹⁰⁶⁾.

Episodes of blood exposure occur frequently in surgical settings. In a Toronto study, based in the operating room, nearly all recognized percutaneous exposures to blood (91%) occurred during suturing⁽¹⁰⁷⁾. Less than 5% of the injuries were reported to occupational health services⁽¹⁰⁷⁾. Researchers have suggested that the continuous occupational exposure to blood and sharp instruments may increase the risk of HIV transmission for surgeons^(49,107,108).

Other studies have identified risk factors for operating room personnel as prolonged operative time, thoracic surgery and gynecologic procedures, and use of fingers to hold tissue that was being sutured rather than use of a surgical instrument^(109-111). For parenteral exposures, suturing accounted for more than one third (36%) of injuries, and activities related to surgical cutting (incising, manipulating sharps, sawing and using power equipment) accounted for an additional 27%⁽¹⁰⁹⁾. Another study found that 77% of needle stick injuries were caused by suture needles⁽¹¹⁰⁾. In one study of surgeons, 86% reported at least one puncture wound in the previous year. This was a much higher rate than had been previously reported⁽¹¹¹⁾.

B. Prevalence of Infection in the Population

Prevalence of infection refers to the number of infected persons in a population at a particular point in time. The prevalence of bloodborne infections varies by disease from one region of Canada to another, from rural to urban areas, and from one city to another. Prevalence data for HIV, HBV and HCV infections in Canada are provided in the respective epidemiologic sections that follow.

C. Risk of Infection Due to Exposure to Bloodborne Pathogens

The risk of infection after exposure to infected blood varies by bloodborne pathogen. The risk of transmission after parenteral exposure to HIV-infected blood is about 0.3%, whereas it is estimated to be up to 100 times greater for HBV (30%) and may be between 3 and 10% for HCV^(40,112).

1. Human Immunodeficiency Virus (HIV)

HIV is the virus that causes acquired immunodeficiency syndrome (AIDS). People with HIV may go on to suffer from AIDS, with a mean incubation period of 10 years. By the end of 1994, it was estimated that 42,000 to 45,000 Canadians had been infected with HIV (unpublished data, Bureau of HIV/AIDS & STD, LCDC, Health Canada). It is estimated that at least 1.5 in 1,000 adult Canadians are infected with HIV^(113,114).

The first AIDS case was diagnosed in Canada in 1982⁽¹¹⁴⁾; in 1996, the number of reported cases totalled 13,810⁽¹¹⁵⁾. After correction for incomplete and delayed reporting it is estimated that the true prevalence of AIDS in Canada is closer to 16,000 cases. Four provinces (British Columbia, Ontario, Quebec, and Alberta) account for 95% of the cases in Canada⁽¹¹⁴⁾.

Studies of inmates in Canadian correctional facilities provide information concerning the prevalence of HIV and AIDS among prisoners and the extent of prior and current high-risk behaviours (e.g., injection drug use, sex for money)⁽¹¹⁶⁾. According to an HIV prison prevalence study of newly admitted inmates in Ontario, approximately 1.23% of females and 0.99% of males admitted to jails, detention and youth centres are infected with HIV. The prevalence of HIV infection among inmates was six times higher than in the general population. Inmates with a history of injection drug use were six to ten times more likely to be HIV positive than those who did not report injecting drugs⁽¹¹⁷⁾. This rate was lower than that found by a study of newly admitted male inmates to medium (4.7%) and minimum security (2.0%) facilities in the province of Quebec⁽¹¹⁸⁾.

Table 1 shows the cumulative incidence of AIDS in Canada by risk factors for men, women and children⁽¹¹⁵⁾. The data are from the Bureau of HIV/AIDS & STD, LCDC, for the quarter ending June 30, 1996.

Table 1 Distribution of Cumulative Reported AIDS Cases in Canada by Exposure Category⁽¹¹⁵⁾

i. Risk of HIV transmission from infected patient/client to worker

For risk factors for HIV, refer to An Integrated Protocol to Manage Health Care Workers Exposed to Bloodborne Pathogens⁽⁵⁾.

The titre of HIV viral RNA is highest at the time of seroconversion and in late symptomatic and advanced disease. Virus titre is important in assessing the risk of seroconversion following an occupational exposure to blood or fluid capable of transmitting bloodborne pathogens.

Epidemiologic studies have shown that the risk of transmission of HIV to HCWs from HIV-infected patients is low, at approximately 0.3% for needle stick exposures^{(51,62-66,96,119)}. International studies have examined HCWs with occupationally acquired HIV infection following percutaneous or mucocutaneous occupational exposure to blood, body fluids, or other clinical or laboratory specimens. Occupationally acquired HIV infections throughout the world number 78* documen-ted seroconversions (i.e., a HCW had a negative baseline post-exposure HIV antibody test result and subsequently seroconverted) and 159* probable seroconversions (i.e., positive HIV antibody test but time of seroconversion was not documented and non-occupational risk factors could not be identified)^{(7,65,67,103,120)}. Needle sticks, scalpel lacerations, and other injuries involving sharp instruments are the major mechanisms for blood-to-blood contact.

The risk of seroconversion following splashes onto non-intact skin or into mucous membranes has been estimated at 0.09%^(34,121). However, no seroconversions from splashes onto non-intact skin or into mucous membranes have been documented in Canada⁽⁷⁾.

All HIV occupational transmission has occurred from exposures to the blood of HIV-infected persons, with the exception of a single instance in which the source was pleural fluid contaminated with blood, and one case of exposure to a laboratory preparation of concentrated virus^(7,67).

A case-control study of HIV seroconversion in HCWs after percutaneous exposure to HIV-infected blood was carried out in France, the United Kingdom and the United States. It was found that an increased risk of HIV infection following percutaneous exposure to HIV-infected blood was associated with three factors: (1) a group of variables related to volume of blood injected (deep injury, procedure involving needle placed directly into source patient's vein or artery, visible contamination of a sharp instrument with patient's blood), (2) terminal HIV illness in the source patient, probably reflecting the higher titre of HIV in blood late in the course of AIDS, and (3) the non-use of zidovudine (ZDV) after exposure^(5,119).

Until 1995, the only person with a probable occupational HIV infection in Canada was a clinical laboratory worker who was presumably exposed to infected blood before 1985, when standards for laboratory handling of potentially infected material were not consistent with today's standards⁽⁶⁸⁾. A second case of probable occupational transmission of HIV in a research laboratory worker in Canada was reported in 1995^(67,122). The British Columbia Centre for Excellence in HIV/AIDS has reported the first case of occupational transmission of HIV in Canada that can be clearly linked to a specific incident. In this case, the health care provider, who was not wearing gloves, sustained a shallow puncture wound from a small-gauge needle. The health care provider believed the injury to be minor. The patient was in the late stage of AIDS, when it is believed that body fluids have elevated concentrations of the virus⁽¹²³⁾.

The National Surveillance of Occupational Exposure to HIV, a voluntary program, (see C. in Appendix, page 43) was initiated in Canada by LCDC in September 1985 to monitor the occurrence of occupational exposures to HIV-infected blood and fluids capable of transmitting bloodborne pathogens. To be included in this study, workers must have sustained a documented exposure - parenteral, mucous membrane or direct contact with non-intact skin - to the blood or body fluids of a patient with AIDS, symptomatic HIV infection, or asymptomatic HIV infection. Injury from needles accounted for the largest portion (60%) of reported exposures; nurses sustained the greatest number (70%) of reported parenteral or mucous membrane exposures (Table 2). While nurses sustained more than half of the exposures that occurred in all occupations, they also represented the greatest number of HCWs and had a higher opportunity for exposure by virtue of their work, such as giving injections. Table 2, therefore, cannot be interpreted as the rate of exposure. No seroconversions have been reported following any of the occupational exposures reported to the National Surveillance of Occupational Exposure to HIV Program in Canada.

Table 2 HIV Exposure by Occupation [July 1, 1996, data from the Bureau of HIV/AIDS & STDs, LCDC]

Table 3 describes the types of exposure to HIV according to the protective apparel worn by the HCW, as documented in the National Surveillance of Occupational Exposure to HIV.

Table 3 HIV Exposure by Protective Apparel Worn [July 1, 1996, data from the Bureau of HIV/AIDS & STDs, LCDC]

Studies of households that include HIV-infected individuals and anonymous serosurveys of hospital and military populations document the lack of viral transmission with casual contact^{(8,28,61,124-129)}. However, transmission of HIV has been reported in homes in which health care has been provided and between children residing in the same household^(130-135). Two cases reported as a result of home health care suggest that HIV infection may, on rare occasions, be transmitted during unprotected contact with blood and other fluids capable of transmitting bloodborne pathogens in the absence of known parenteral or sexual exposure to these fluids^(131,133). In one case, a 5-year-old child was infected by his mother, who had AIDS. Infection was probably a result of direct exposure to purulent and bloody exudates from the mother's open skin lesions, possibly facilitated by the child's broken skin and the mother's manipulation of the child's skin lesions. In the second case, a mother became infected while providing nursing care for her son during the 6 weeks before his death from AIDS. She had direct contact with her son's urine and feces, which may have had occult blood. In addition, she could have had other unrecognized or unrecalled exposures to her son's blood⁽¹³¹⁾. In addition to these two reported cases, six previous reports have described household transmission of HIV not associated with sexual contact, injection drug use, or breast feeding. Of these eight reports, five were associated with documented or probable blood contact^{(131,133-135)}. In the sixth report, HIV infection was found in a boy after his younger brother had died as a result of AIDS; however, a specific mechanism of transmission was not determined^(130,131). Two reports involved nursing care of terminally ill persons with AIDS in which a blood exposure might have occurred but was not documented; in both reports, skin contact with body secretions and excretions occurred⁽¹³¹⁾.

ii. Risk of HIV transmission from HCW to patient/client and between patients/clients

NOTE: For an update regarding HIV transmission from HCWs to patients, refer to the Recommendations from the Consensus Conference on Infected Health Care Workers: Risk for Transmission of Bloodborne Pathogens, scheduled to be published as a supplement to the Canada Communicable Disease Report in mid-1997.

There is one proven case of a patient acquiring HIV infection from an infected HCW^(11,69-72). However, while HIV-infected HCWs have not otherwise been a source of patient infection, certain patient care practices, whether or not the HCW was HIV-positive, have been shown to have the potential to expose the patient to HIV.

a. Six patients became infected while receiving care from one U.S. dentist with HIV infection. Despite extensive searches for other instances of HIV transmission associated with dental practice, this was the only documented outbreak found. The specific mode of transmission was not identified despite intensive investigation, although epidemiologic evidence and deoxyribonucleic acid (DNA) sequencing implicated the dentist's virus as the source of these infections.

Investigators found that infection control practices in the dental clinic did not meet recommended standards. For example, no written policy or training course on infection control principles or practice was provided for staff. No office protocol existed for reporting or recording injuries from needle sticks or other percutaneous injuries involving sharp instruments or devices. Anesthetic needles were either recapped by the dentist using a two-handed technique or left uncapped and then recapped by the assistant using a two-handed technique. Staff did not always change gloves between patients. On occasion, staff washed their gloves rather than change them between patients. The dental practice had no written protocol or consistent pattern for cleanup and instrument reprocessing. Equipment was cleaned and disinfected inconsistently. Some disposable items were reused without quality control. Investigations following this outbreak suggested that some reusable dental equipment may have the potential to cross-contaminate^{(69,70,72-74,136,137)}. In another dental study, infective viral particles were recovered from internal mechanisms of handpieces, connecting air and water hoses, and from water spray expelled when the equipment was reused ⁽⁷³⁾.

b. Errors in the intravenous injection of blood or blood products during nuclear medicine procedures have resulted in several cases in which HIV-infected blood cells have been inadvertently injected into patients, resulting in iatrogenic HIV infection. The incidents were caused by hospital personnel failing to identify correctly the patient and/or the blood cells to be injected, or by the improper handling and disposal of used syringes^(138,139).

c. Poor compliance with aseptic techniques (e.g., contamination of multi-dose vials, use of a single syringe to administer medication to different patients, and contamination of syringes and catheters) have all been implicated in the transmission of bloodborne pathogens^(140-143). Research has shown that the reuse of single-use syringes and needles has caused the contamination of multi-dose local anesthetic vials, and that HIV can survive in local anesthetics⁽¹⁴⁰⁾. Use of a multi-dose local anesthetic vial, which was potentially contaminated by re-used syringes, is believed to have been the cause of multiple patient-to-patient transmission of HIV in a surgical clinic in Australia^(95,144). Actual in-use multi-dose vials (i.e., heparin and insulin vials) have been shown to be contaminated with red blood cells⁽¹⁴²⁾.

d. Inadequate sterilization of needles used for intravascular and intramuscular injections have caused cross-contamination of HIV^(85,145).

e. HIV infection is reported to have been transmitted in a hemodialysis setting, probably as a result of inadequate reprocessing or inadvertent reuse of hypodermic needles⁽⁸⁵⁾.

f. There are reports of bloodborne pathogen transmission in residential settings, characteristically involving intimate contact, such as shared razors, or provision of medical care without the precautions recommended in Section III being observed^(130-134). However, follow-up family studies show that transmission of HIV in the home, outside of sexual exposure, rarely occurs^(124,125).

2. Hepatitis B Virus (HBV)

HBV is a double-stranded DNA virus with three major antigens known as surface antigen (HBsAg), e antigen (HBeAg), and core antigen (HBcAg). The presence of HBsAg can be detected in serum 30 to 60 days after infection. The incubation period for hepatitis B is 45 to 160 days (average 120 days). Antibody to surface antigen (anti-HBs) appears in serum after the infection has resolved and confers long-term immunity. HBcAg is not measurable in serum with currently available tests. Antibody to core antigen (anti-HBc) develops in all HBV infections and persists indefinitely. Immunoglobulin M antibody to the core antigen (IgM anti-HBc) is a marker of recent HBV infection. HBeAg in serum is associated with viral replication and high infectivity. Antibody to the hepatitis B e antigen (anti-HBe) indicates reduced viral replication and lower infectivity. However, any serum containing HBsAg is considered infectious⁽¹⁴⁶⁾. In individuals with HBV infection, 90% to 95% become immune and 5% to 10% become carriers.

Canada is an area of low endemicity for hepatitis B. Less than 5% of Canadians are hepatitis B antibody-positive and less than 0.5% are HBsAg-positive. The annual rate of new cases of acute hepatitis B reported in Canada doubled from 1980 to 1990, possibly because of improved detection, and since 1990 has remained stable at about 10 cases per 100,000. There is substantial regional variation, from a low of 0.7 cases per 100,000 in Newfoundland to a high of 33.9 cases per 100,000 persons in British Columbia^(146,147).

LCDC established the Sentinel Health Unit Surveillance System to provide reliable demographic, risk factor and other epidemiological and laboratory data for the development of public health policy⁽¹⁴⁸⁾. Nine health units in eight provinces, representing approximately 10% of the Canadian population, participated in the System. The Sentinel Health Unit Surveillance System carried out targeted surveillance for viral hepatitis (A, B, and C) to determine the incidence of and risk factors for viral hepatitis, to determine the personal and economic costs of the disease and to evaluate current control measures. In 1995 it identified 376 newly diagnosed cases of hepatitis B. Of these individuals, 34% had a history of multiple sexual partners, 83% had a history of injection drug use (IDU), and 35% had a history of at least one sexually transmitted disease (STD)⁽¹⁴⁹⁾.

The prevalence of HBV infection is higher in certain ethnic populations and occupational categories, and in some geographic regions. HBV infection, unlike other bloodborne pathogens, is preventable through vaccination, which provides protection against infection in 90% to 95% of recipients^(75,146). Before the introduction of vaccine programs for high-risk groups, the prevalence was estimated to be high (often exceeding 20%) in men who had sex with men, injection drug users (IDUs), pathologists and technologists in biochemistry and hematology laboratories, hemodialysis unit staff, hemophiliacs, residents of institutions for the developmentally challenged, and immigrants from South East Asia (refer to An Integrated Protocol to Manage Health Care Workers Exposed to Bloodborne Pathogens⁽⁵⁾).

The prevalence was intermediate (7% to 20%) in hospital nurses, laboratory technologists other than those in the high prevalence category, dentists, and staff in institutions for the developmentally challenged. Prevalence was low (7%) in administrative hospital staff, medical and dental students, blood donors, and other healthy adults^(146,150). All data are from the pre-vaccination era.

The incidence of HBV infection has decreased among HCWs since the introduction of the hepatitis B vaccine^{(84,98,151-155)}.

i. Risk of HBV transmission from infected patient/client to worker

HBV infection is a recognized occupational hazard for workers who are exposed to blood or fluids capable of transmitting bloodborne pathogens^{(24,71,75,94,146,150,156-159)}. For example, in a survey of practising embalmers in Alberta, 5.2% of respondents reported occupational acquisition of HBV infection (unpublished observations, EA Henderson, Alberta).

In 1992 in the United States, the CDC estimated that 6,800 nonvaccinated HCWs whose jobs entail exposure to blood become infected with HBV each year, 250 are hospitalized as a result of acute complications and approximately 100 will die from cirrhosis, liver cancer, or fulminant hepatitis⁽⁴²⁾.

The 1993 study in 34 primary care clinics in Montreal revealed that only 52% of personnel exposed to blood had been vaccinated against hepatitis B⁽¹⁰⁶⁾.

As with HIV exposures, sharps injuries account for the majority of the sources of infection⁽²⁴⁾. Studies have shown that nonvaccinated HCWs who have been exposed through needle stick injury to the blood of a patient who is HBeAg-positive acquire the infection in 19% to 30% of cases, even after prophylaxis with hepatitis B immune globulin⁽⁹⁸⁾. In contrast, an HBeAg-negative exposure results in transmission to less than 5% of health care workers, suggesting a minimum concentra-tion of hepatitis B virus particles is necessary for transmission⁽⁹⁸⁾.

ii. Risk of HBV transmission from HCW to patient/client and between patients/clients

NOTE: For an update regarding HBV transmission from HCWs to patients, refer to the Recommendations from the Consensus Conference on Infected Health Care Workers: Risk for Transmission of Bloodborne Pathogens, scheduled to be published as a supplement to the Canada Communicable Disease Report in mid-1997.

From the 1970s, when testing for HBV serologic markers became available, through December 1994, HBV transmission from 42 infected HCWs to patients has been recognized in developed countries. Thirty-eight HCWs were surgeons or dentists⁽¹⁶⁰⁾; the remaining four performed more minor invasive procedures (e.g., intramuscular injections or venipunctures, arterial punctures for blood gases, operation of a cardiac bypass pump)⁽⁷¹⁾. In non-hospital settings, HBV has been transmitted from worker to client and from client to client. HBV transmission in day-care and residential settings is presumed to have occurred through bites, scratches or open skin lesions^{(78,159,161-163)}.

Dentists, oral surgeons and other dental care workers have been the source of many HBV transmissions to patients⁽⁷⁶⁾. In some settings, HBV was transmitted to patients through exposure to contaminated solutions (e.g., use of multi-dose vials in a hemodialysis unit and a dermatology clinic) or equipment, including finger-stick devices for glucose monitoring, acupuncture needles, tattoo needles, and a jet injector gun (in a weight-reduction clinic)^{(77,79,80,164-166)}. HBV has been transmitted from patient to patient through inadequately cleaned and disinfected endoscopes and biopsy forceps^(167,168).

In Canada two cases of nosocomial hepatitis B were identified following surgical procedures by an infected orthopedic surgeon. The surgeon was HBeAg-positive at the time of the surgery⁽⁸¹⁾.

Transmission of HBV in hemodialysis units has been studied extensively^(89,90,94). Before the United States issued recommendations for the control of hepatitis B in hemodialysis centres in 1977, the incidence of HBV infection among patients and staff members in these centres had reached 6.2% and 5.2% respectively^(84,151). With the introduction of infection prevention and control measures⁽⁸⁴⁾, the incidence and prevalence of HBV infection among hemodialysis centre patients and staff declined from 1976 to 1983. This trend was evident before the introduction of hepatitis B vaccination, which underscores the importance of UP to prevent occupational bloodborne infections⁽¹⁵¹⁾.

3. Hepatitis C Virus (HCV)

HCV is a single-stranded, enveloped, ribonucleic acid (RNA) virus. HCV is classified as separate genus (Herpacavirus) in the Flaviviridae family. Through nucleic acid sequencing at least six major genotypes and more than 80 subtypes have been identified worldwide. Genotypes 1 and 2 appear to be the most common ones in Canada. Antibody to HCV (anti-HCV) can be detected by third generation enzyme-linked immunosorbent assays (ELISAs) in serum 6 to 8 weeks after exposure. Reverse transcriptase polymerase chain reaction (PCR) can detect the presence of RNA in serum as early as 1 to 2 weeks after exposure.

Hepatitis C is one of Canada's five most frequent laboratory-diagnosed viral infections⁽¹⁶⁹⁾. The screening tests for HCV became available only in 1990, and the sensitivity and specificity of antibody detection by serologic tests is still improving. Routine tests currently available cannot distinguish between acute, chronic and resolved infection.

In 1994, 2,856 cases of hepatitis C were reported to LCDC from eight provinces and territories through the national notifiable disease reporting system. Provisional data indicate greatly increasing numbers of reports in 1995 (14,070 cases) and 1996.

In LCDC's Sentinel Health Unit Surveillance System⁽¹⁴⁸⁾, 958 cases of hepatitis C infection (both acute and chronic) were identified between October 1993 and March 1995. Risk factor history among these cases included (these are not mutually exclusive) IDU (70.8%), blood transfusion (5.5%), IDU and blood transfusion (16.6%), multiple sex partners in the last six months (17%), and at least one STD (25%) (unpublished data).

Two of every thousand new blood donors in Canada in 1996 had antibodies to hepatitis C (anti-HCV) (unpublished data, Canadian Red Cross Society).

It is estimated that 1% of the Canadian population has been infected with HCV. It is important to note that estimating the incidence of HCV infection from passive surveillance programs, such as the ones just mentioned, is not possible, since only 5% to 25% of people with new HCV infections are ill enough to seek medical attention^(170,171). As many as 90% of people newly infected with HCV remain healthy for some time, but they continue to carry the virus and may be infectious. HCV infection is characterized by its high rate of chronicity; 60% to 80% of infected individuals develop chronic liver disease of varying degrees of severity, including cirrhosis in 20% of cases and, more rarely, hepatocellular carcinoma^(172,173). The high level of chronicity indicates that in most persons a protective immunity does not develop. This, and the existence of several HCV genotypes, presents a problem in developing a vaccine to protect against HCV⁽¹⁷³⁾.

At present, the major mode of transmission of HCV in Canada is injection drug use. Transmission through blood and blood products is now rare since testing of donations began in 1990. Certain personal services may pose a significant risk (e.g., tattooing). The risk of transmission through other routes, such as sexual contact or household transmission, appears to be low^{(170,174,175)}.

Canadian studies of HCV seroprevalence in federal penitentiaries have shown the following: (a) at the Prison for Women in Kingston, Ontario, 113 (87%) inmates were tested and 39.8% were positive for HCV⁽¹⁷⁶⁾; (b) at a male penitentiary for men near Kingston, Ontario, 408 (69%) inmates were tested and 28% were positive for HCV⁽¹⁷⁷⁾; (c) among 23% of inmates tested in a male federal penitentiary in British Columbia, 28% were positive for HCV⁽¹⁷⁸⁾. Seropositivity for HCV in the prison population likely indicates injection drug use, but may also result from other risk factors, such as unsafe sexual behaviour, tattooing and other skin piercing activities.

There have been numerous cross-sectional seroprevalence studies of HCV carried out in Canada and around the world. International studies have described increased prevalence of infection in persons undergoing hemodialysis and in household contacts^(179-181). In addition, HCV infection of certain organ recipients has been documented (e.g., after liver transplantation). However, these rates depend on the prescreening practices and policies regarding use of organs from HCV-positive persons. In Canada at this time, tissue donors are not routinely screened for HCV. National standards regarding tissue and organ donation will be available in 1997.

The risk factors for HCV transmission in occupational settings are not well defined^(40,182), though are thought to include the degree of contact with blood or sharp instruments and the prevalence of anti-HCV among patients⁽¹⁸³⁾. Early studies of HCWs with a high degree of blood exposure concluded that HCV seroprevalence was low and was similar to the seroprevalence rates reported for volunteer blood donors ^(184-186). Since the introduction of hepatitis B vaccine over the past decade, HCV has replaced HBV as the most commonly identified cause of viral hepatitis among HCWs⁽⁹⁹⁾. Exposures to needle sticks and sharps were the most common causes of occupational transmission of HCV^{(98-100,112,187-190)}. There is a reported case of transmission of HCV from a blood splash to the conjunctiva⁽¹⁰⁰⁾. A low concentration of virus may be present in saliva⁽¹⁹¹⁾. At least one case is attributed to a human bite^(192,193). HCV has been frequently transmitted in hemodialysis units^{(88,91,94,194-196)}.

NOTE: For an update regarding HCV transmission from HCWs to patients, refer to the Recommendations from the Consensus Conference on Infected Health Care Workers: Risk for Transmission of Bloodborne Pathogens, scheduled to be published as a supplement to the Canada Communicable Disease Report in mid-1997.

4. Other Bloodborne Pathogens

No data exist to suggest that human T-cell lymphotrophic virus (HTLV) type I or II or Epstein-Barr virus are transmitted to HCWs in health care settings. Studies on HTLV-I and II indicate that sexual contact, blood transfusion, and shared injection drug paraphernalia rather than casual contact are risk factors for acquisition⁽¹⁹⁷⁾. The Canadian Red Cross screens donors for HTLV-I and II, HIV, HBV, HCV, and syphilis to decrease the possibility of their transmission through transfusion of blood and blood products.

Transmission of CMV requires close contact between mucous membranes or direct inoculation of mucous membranes with fresh secretions. The virus is found in cervical fluid, vaginal secretions, semen and blood. Occupational acquisition can be prevented by hand washing after handling diapers or respiratory secretions⁽¹⁹⁸⁾. Studies that compare the prevalence of CMV antibody in HCWs and other groups have not found any significant increase in antibody positivity in HCWs^(199-201).

Guidelines to prevent the transmission of these three viruses will be similar to those that follow for HIV, HBV and HCV.

Viral hemorrhagic fevers (e.g., Ebola Fever, Lassa Fever) are transmissible in blood and fluids capable of transmitting bloodborne pathogens in health care settings. Recommendations for the prevention of these rare diseases are more rigorous than those for other bloodborne pathogens. Canadian recommendations have existed since 1986 and have undergone regular revision. The latest revision was published in January 1997⁽²⁰²⁾.

(* Documented cases: Canada - 1, U.S. - 51, Europe - 26 / Probable cases:  Canada - 2, U.S. - 108, Europe - 43, Mexico - 6 )

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