Recent Canadian experience with targeted hepatitis C virus lookback

Epidemiology of Hepatitis C over 28 years of monitoring Canadian blood donors: Insight into a low-risk undiagnosed population

BACKGROUND

Hepatitis C is a blood-borne infection with the hepatitis C virus (HCV) that can progress to cirrhosis and liver cancer. About 70% (50-80%) of infections become chronic and exhibit anti-HCV and HCV nucleic acid (NAT) positivity. Direct acting oral pan genotypic antiviral treatment became available in 2014 and was free for most Canadians in 2018. Clinical screening for HCV infection is risk-based. About 1% of Canadians have been infected with HCV, with 0.5% chronically infected (about 25% unaware) disproportionately impacting marginalized groups. Blood donors are in good health, are deferred for risks such as injection drug use and can provide insight into the low-risk undiagnosed population. Here we describe HCV epidemiology in first-time blood donors over 28 years of monitoring.

METHODS

All first-time blood donors in all Canadian provinces except Quebec (1993 to 2021) were analyzed. All blood donations were tested for HCV antibodies (anti-HCV) and since late 1999 also HCV NAT. A case-control study was also included. All HCV positive donors (cases) since 2005 and HCV negative donors (1:4 ratio controls) matched for age, sex and location were invited to complete a risk factor interview. Separate logistic regression models for anti-HCV positivity and chronic HCV assessed the association between age cohort, sex, region and neighbourhood material deprivation and ethnocultural concentration.

CASE

control data were analysed by logistic regression.

RESULTS

There were 2,334,238 donors from 1993 to 2021 included. Prevalence for anti-HCV was 0.33% (0.30,0.37) in 1993 and 0.07% (0.05,0.09) in 2021 (p < 0.0001). In 2021 0.03% (0.01,0.04) had chronic HCV. Predictors for both anti-HCV positivity and chronic HCV were similar, for chronic HCV were male sex (OR 1.8, 1.6,2.1), birth between 1945 and 1975 (OR 7.1, 5.9,8.5), living in the western provinces (OR 1.4, 1.2,1.7) and living in material deprived (OR 2.7, 2.1,3.5) and more ethnocultural concentrated neighbourhoods (OR 1.8, 1.3,2.5). There were 318 (35.4%) of chronic HCV positive and 1272 (39.6%) of controls who participated in case control interviews. The strongest risks for acquisition were injection drug use (OR 96.9, 22.3,420.3) and birth in a high prevalence country (OR 24.5, 11.2,53.6).

CONCLUSIONS

Blood donors have 16 times lower HCV prevalence then the general population. Donors largely mirror population trends and highlight the ongoing prevalence of untreated infections in groups without obvious risks for acquisition missed by risk-based patient screening.

The epidemiology of human T-cell lymphotropic virus types I and II in Canadian blood donors

OBJECTIVES

Blood donors in Canada have been tested for Human T-Cell Lymphotropic Virus (HTLV) since 1990. We report the epidemiology, risk factors and lookback/traceback of HTLV-positive donors/recipients.

METHODS

The annual HTLV rate was calculated from 1990 to 2010. Residual risk was estimated as the product of incidence and window period. Twenty-nine HTLV-positive donors and 116 matched controls (ratio 1 : 4) were interviewed about risk factors. For HTLV-positive donations, lookback investigations involved identification of all previous donations, and attempting to locate and test recipients. Traceback was initiated when transfusion transmission was queried for HTLV-positive blood recipients. All donors of products that the recipient received were identified, with an attempt to locate and test them.

RESULTS

The HTLV rate decreased from 9.35 per 100,000 donations in 1990 to 1.11 in 2010. The residual risk of infection was 1 in 7.6 million donations. In logistic regression birth overseas (OR 18.7), history of sexually transmitted diseases (OR 32.9), sex with unknown background (OR 5.4) and blood transfusion (OR 8.9) were significant predictors. In the lookback study, of 109 HTLV-positive donors, 508 components were transfused, of whom 147 recipients were tested and 18 (12%) were positive. All were transfused prior to the implementation of donor testing. Twenty-three traceback investigations were requested involving 324 transfused untested products,of whom 219 (67.6%) of donors were tested and 13 (6%) were positive for HTLV.

CONCLUSIONS

With testing of the blood supply, the risk from HTLV is very low and while most HTLV-positive donors have risk factors, deferrable risk is rare.

Surveillance of transfusion-transmissible infections comparison of systems in five developed countries

Most industrialized countries maintain surveillance programs for monitoring transmissible infection in blood donations, revising approaches to methodology and risk assessment as new threats emerge. A comparison of programs in the United States, Canada, France, the UK, and Australia indicates that they have similar function, although the structure of blood programs vary as does the extent and nature of formal ties with public health. The emergence of HIV in the late 1970s and early 1980s was key in recognizing that surveillance systems specific to blood transfusion were essential. Hence, most industrialized countries monitor transfusion-transmissible infections in donors and evaluate the impact of new testing and of predonation screening strategies. Emerging infections since HIV have had different transmission pathways and challenged blood programs to draw upon resources for a rapid and effective response, with recognition that the original focus on sexual/drug-related risk of HIV and hepatitis was inadequate. The focus of surveillance programs on new and emerging pathogens fulfills a key role in risk assessment and policy formulation. The precise nature of such activities varies by country because of the structure of the blood programs and surveillance systems, the strategic focus of the blood programs, and the epidemiology of disease in each country.

Using mass media and the Internet as tools to diagnose hepatitis C infections in the general population

BACKGROUND

Many individuals with hepatitis C virus (HCV) infection are undiagnosed.

PURPOSE

This study describes the development and the use and outcomes of a mass media campaign, combined with an Internet risk assessment and an Internet-mediated blood-testing procedure for HCV to identify individuals infected with HCV in the general population.

METHODS

From April 2007 to December 2008, individuals in HCV risk groups were referred to an online, previously validated risk-assessment questionnaire at www.heptest.nl. Individuals at risk could download a referral letter for a free, anonymous HCV blood test in a nonclinical setting. Test results could be obtained online, 1 week later, using a personal log-in code. Anti-HCV-positive participants were requested to visit the Public Health Service for confirmation and RNA testing. Chronically HCV-infected individuals were referred for treatment. Data were analyzed in 2009-2010.

RESULTS

The website attracted 40,902 visitors. Of the 9653 who completed the questionnaire, 2553 were at risk for HCV (26.4%). Main reported risk factors were a blood transfusion prior to 1992 and noninjecting drug use. Of the 1480 eligible for the blood test, 420 opted for testing (28%). HCV antibodies were detected in 3.6% (n=15, 95% CI=2.1%, 5.7%); of the 12 with a chronic HCV infection, six began treatment.

CONCLUSIONS

Internet-mediated risk-based testing for HCV has proved to be a feasible and effective strategy to identify undiagnosed HCV infection in the general population. All HCV-infected individuals belonged to hard-to-reach populations. Test uptake was 28%, which is high for an online project that includes blood testing. Because Internet-mediated testing is low-cost, this strategy holds promise for future screening.

Declining hepatitis C rates in first-time blood donors: insight from surveillance and case-control risk factor studies

BACKGROUND

Hepatitis C virus (HCV) rates have decreased steadily in first-time donors in Canada since testing was implemented but reasons are unclear. A description of factors that may have played a role in this decline is reported.

STUDY DESIGN AND METHODS

Descriptive analysis of first-time blood donors by HCV positivity status and year (1993--2006), sex, and age was carried out. HCV-positive first-time donors and matched controls participated in a confidential scripted telephone interview about risk factors in 1993 through 1994 and in 2005 through 2006, and risk factors independently predicting HCV positivity were determined with multiple logistic regression.

RESULTS

HCV-positive donations occurred most frequently in donors born between 1945 and 1964 and decreased in this birth cohort over time (p < 0.01). At present, most first-time donors (74%) are born after 1964. History of intravenous drug use, sex with an intravenous drug user, blood transfusion, and tattoo independently predicted (p < 0.01) HCV positivity in both periods (1993--1994 and 2005--2006).

CONCLUSION

Most HCV-positive donors were born between 1945 and 1964, and the decline in HCV rates is associated primarily with this birth cohort. The key risk factors predicting HCV positivity did not change over the 13 years of the study. With approximately two-thirds of HCV-positive Canadians in the general population having been tested for HCV, potential donors may be aware of their HCV status and be likely to self-defer. This, and an increasing proportion of first-time donors born after 1964, may contribute to declining HCV rates in first-time donors.

Hepatitis B virus DNA-positive, hepatitis B surface antigen-negative blood donations intercepted by anti-hepatitis B core antigen testing: the Canadian Blood Services experience

BACKGROUND

The benefit of introducing anti-hepatitis B core antigen (HBc) screening for intercepting potentially infectious donations missed by hepatitis B surface antigen (HBsAg) screening in Canada was studied.

STUDY DESIGN AND METHODS

Anti-HBc testing of all donations was implemented in April 2005, along with antibody to hepatitis B surface antigen (anti-HBs) and hepatitis B virus (HBV) DNA supplemental testing of anti-HBc repeat-reactive, HBsAg-negative donations. The proportion of potentially infectious donations intercepted by anti-HBc over the initial 18 months of testing was calculated based on three assumptions relating infectivity of HBV DNA-positive units to anti-HBs levels. Lookback was conducted for all DNA-positive donations.

RESULTS

Of 493,344 donors, 5,585 (1.13%) were repeat-reactive for the presence of anti-HBc, with 29 (0.52%) being HBV DNA-positive and HBsAg-negative. The proportion of potentially infectious donations intercepted by anti-HBc screening was 1 in 17,800 if all HBV DNA-positive donations were infectious, 1 in 26,900 if infectivity was limited to donations with an anti-HBs level of not more than 100 mIU per mL, and 1 in 69,300 if only donations with undetectable anti-HBs were infectious. For 279 components in the lookback study, no traced recipients were HBsAg-positive and 7 recipients were anti-HBc-reactive in association with 4 donors, 3 of whom had an anti-HBs level of more than 100 mIU per mL and 1 of whom had a level of 61 mIU per mL.

CONCLUSION

Implementation of anti-HBc screening reduced the risk of transfusing potentially infectious units by at least as much as had been expected based on the literature. The lookback did not provide proof of transfusion transmission of HBV from HBV DNA-positive, anti-HBc-reactive, HBsAg-negative donors but it did not establish lack of transmission either.

Evaluating the impact of public health notification of suspected transfusion-transmissible hepatitis C virus infection and effectiveness of lookback and traceback investigations by Canadian Blood Services in British Columbia, Canada, August 2002 through F

BACKGROUND

Suspected transfusion-transmissible infections (TTIs) have been reported to public health (PH) in British Columbia (BC) since August 2002. The impact of PH notification of suspected transfusion-transmissible hepatitis C virus (TT-HCV) infection over the first 2.5 years and the effectiveness of HCV lookback (LB) and traceback (TB) investigations conducted by Canadian Blood Services (CBS) in BC were evaluated.

STUDY DESIGN AND METHODS

Suspected TT-HCV cases reported to CBS in BC between August 28, 2002, and February 28, 2005, were analyzed. The incremental yield of plausible TTIs from PH-reported suspected TTIs was calculated. The effectiveness of LB and TB investigations was assessed with respect to the impact of improved anti-HCV donor screening, the number of newly recognized HCV infections, and the timeliness of initiating investigations.

RESULTS

Nine of 553 (1.6%) investigations were initiated after PH reporting, yielding an additional 2 of 237 (i.e., 0.8%) plausible TTIs. Ninety-two percent of investigations with transfused units involved transfusions before implementing second-generation anti-HCV enzyme immunoassay (EIA) donor screening. Almost one-third of HCV-infected persons in linked investigations (i.e., LB triggered by a TB and vice versa) were newly identified. Recently tested, PH-reported cases incurred a mean delay exceeding 6 months until initiating a LB or TB investigation.

CONCLUSION

PH reporting of TTIs and investigating transfusions after second-generation anti-HCV EIA donor screening identified few plausible TT-HCV infections. Many HCV-infected recipients or lapsed donors first became aware of their infection status as a result of CBS investigations. The current process of reporting suspected TTIs incurs significant time delay.

Effectiveness of human T-lymphotropic virus (HTLV) recipient tracing (lookback) and the current HTLV-I and -II confirmatory algorithm, 1999 to 2004

BACKGROUND

This study reports on the efficacy of an investigational human T-lymphotropic virus (HTLV)-I and -II lookback program in the context of differing confirmatory testing algorithms.

STUDY DESIGN AND METHODS

The results of testing approximately 35 million donations for anti-HTLV-I and -II were evaluated for two recent periods reflecting the use of two different confirmatory algorithms. The number of seroconverting donors was established for the entire period, and the results of lookback on their prior donations were investigated.

RESULTS

The dual enzyme immunoassay (EIA) strategy was used throughout both study periods and resulted in a 57 to 76 percent reduction in the number of samples requiring confirmatory testing. From May 2000 to February 2002, a total of 9138 samples were repeatedly reactive by the primary screening test; of the concordant EIA-reactive samples, 461 (12%) were confirmed by Western blot, whereas 3083 (79%) were indeterminate. From March 2002 to December 2004, a total of 21,291 samples were repeatedly reactive; of the concordant EIA-reactive samples, 1099 (22%) were confirmed by the State of California's reference laboratory and only 273 (5%) were equivocal. Overall, 38 or 1 in 921,000 donations were from a seroconverting donor with 32 prior donations within the lookback period. Of those 32, components from only 11 were transfused to recipients who survived; of these, 4 were tested and all were nonreactive for HTLV-I and -II antibodies.

CONCLUSION

Use of creative algorithms can increase the efficacy of anti-HTLV-I and -II confirmatory testing and reduce the number of indeterminate results. Currently, lookback for HTLV-I and -II has a very low yield, and its public health benefit is questionable.