What Hepatitis C Virus (HCV) Diagnostic Tools Are Needed to Advance Diagnosis of Current HCV Infection in Outreach Settings and in a Nonclinical Setting?

Abstract

Given the growing hepatitis C virus (HCV) epidemic in the United States, it is imperative to implement a coordinated, equitable public health approach to HCV testing that will facilitate immediate access to treatment, especially for individuals with limited healthcare access and those who inject drugs. Point-of-care RNA diagnostic tests have the greatest potential to address this need. Future regulatory approval has been facilitated by a recent change in the US Food and Drug Administration's approach to evaluating point-of-care diagnostic tests that have been developed and validated.

Approximately 2.2 million noninstitutionalized adults had hepatitis C virus (HCV) infection in the United States (US) during January 2017–March 2020 [1–5]. Awareness of HCV infection is suboptimal, as only 49%–55% of people with chronic disease are aware of their infection status [6–8]. Underdiagnosis of HCV remains one of the most significant barriers to HCV elimination as a public health threat.

Diagnosis of HCV infection has historically involved the use of blood tests to detect antibodies (anti-HCV), HCV core antigen (where ever available), and HCV RNA [9]. Other key tests include those for transaminases, liver function, and inflammation to help evaluate tissue damage; biopsy to determine the histologic evidence of liver damage; ultrasound; elastography (which uses ultrasound to measure liver stiffness caused by fibrosis); and computed tomography or magnetic resonance imaging to determine the presence of hepatocellular carcinoma. Together, these tools for diagnosis and disease evaluation inform the best course of treatment. However, most, if not all these tests are conducted in clinical settings and involve significant time and financial burden.

Point-of-care (POC) testing refers to diagnostic tests that can be performed quickly and accurately at or near sites where persons who will benefit from care are encountered, without the need for laboratory-based testing. In the context of HCV diagnosis, POC testing offers the most efficient way to diagnose HCV infection and to rapidly link patients to curative treatment and follow-up care. People who inject drugs (PWID) have the highest incidence of HCV infection, but often face significant challenges to effective care, including limited access due to lack of insurance, stigma, unstable housing, transportation obstacles, poor health literacy, and poverty [10]. POC testing offers the most expeditious way to screen and diagnose HCV infections among PWID and provide immediate linkage to care and treatment, so that ultimately we can make significant progress in decreasing the population burden of HCV infection and achieve the World Health Organization (WHO) and US Department of Health and Human Services goal of global HCV elimination [11, 12].

In the US, the most commonly used HCV POC test is the rapid anti-HCV test [13]. Although HCV core antigen and rapid HCV RNA test platforms have been developed and have good performance characteristics [14, 15], core antigen testing is not available in the US and only laboratory-based RNA testing is currently available. The advantages of the rapid anti-HCV test, including speed, convenience, and accessibility, are greatly outweighed by the inability to distinguish persistent HCV infection from previous resolution of infection, nor does it distinguish acute infection from chronic disease [16]. While the anti-HCV POC test facilitates screening for exposure to HCV, it is not helpful for treatment decisions without additional testing. Also, as the window period for detection of anti-HCV is long, this approach does not identify acute or recent infection, when transmission risk may be high [16, 17]. The value of HCV antigen tests and rapid HCV RNA testing is the actionable results they provide [18], which is especially important when dealing with populations for whom a follow-up visit for confirmatory testing is far from assured. While antigen testing is more likely than antibody testing to detect HCV in the early stages of infection [19], cost and limited sensitivity impact its utility. These tests are especially useful in settings where molecular testing is not available, but antigen detection is not likely to be further developed as a diagnostic tool in the US given US Food and Drug Administration (FDA) guidance. Rapid HCV RNA tests, which detect HCV genetic material, offer the greatest advantage for diagnosis and rapid initiation of treatment as the presence of HCV RNA confirms current infection [20]. HCV RNA testing in the US is conducted in laboratories using reverse-transcription polymerase chain reaction (RT-PCR) testing on serum or plasma obtained by venipuncture following receipt of a reactive anti-HCV test. RT-PCR, a highly sensitive and specific method for detecting and quantifying viral RNA in blood samples, is considered the gold standard for HCV RNA detection. The lack of a POC option for HCV RNA testing in the US is a significant impediment to the rapid diagnosis and swift initiation of treatment—especially in nontraditional settings—impacting the ability to address the HCV epidemic in the highest risk groups and, eventually, to eliminating HCV.

POC HCV RNA testing is especially important in diagnosing HCV infection in nontraditional settings, such as syringe services and outreach programs and other nonclinical settings trusted by the populations at highest risk, so that rapid linkage to curative treatment and follow-up care can be facilitated. A significant advantage of POC HCV RNA testing is the provision of an accurate diagnosis with a single minimal blood sample, obviating the need to bring persons with a positive anti-HCV result back for confirmatory testing, which is a significant obstacle in the cascade of care. These platforms can be used in remote or resource-limited settings where laboratory personnel and facilities are limited [21]. POC RNA testing is one of the most important tools needed to increase HCV testing rates and improve access to curative treatment for HCV-infected individuals. It is clear that POC HCV RNA testing platforms with fast turnaround times, ease of use (including potentially the ability to self-test), low cost, and accuracy of diagnosis are needed in the US to achieve HCV elimination [20, 22–24].

THE OPTIMAL DIAGNOSTIC TOOLS

In October 2021, the Association of Public Health Laboratories, in collaboration with the Centers for Disease Control and Prevention (CDC), organized a 2-day meeting entitled “Identifying High-Priority Diagnostic Approaches for Advancing Hepatitis C Elimination in the US” that brought together experts from public health laboratories, clinicians, researchers, and their colleagues from the FDA and CDC [25]. The panelists and participants proposed the following criteria for a POC diagnostic platform: simple to conduct, minimally invasive, rapid results, accurate, low cost, potential for self-testing, and widespread availability. To be simple, the test should require minimal equipment and training to perform. The test would use capillary blood, a minimally invasive procedure, eliminating need for venous access and skilled phlebotomists. Results should be available in 1 hour or less—ideally, in <30 minutes. It should have optimal accuracy—that is, the same or better sensitivity and specificity characteristics as similar FDA-approved RNA laboratory-based diagnostic tests currently available—and meet all necessary requirements for a Clinical Laboratory Improvement Amendments (CLIA) waiver. A CLIA waiver, issued by the FDA, ensures that a particular test meets certain standards for its design, performance, and reporting, and that it can be performed by nonlaboratory personnel, such as a healthcare worker or even a patient at home [26, 27]. A CLIA waiver indicates that the FDA has determined that the test is simple and safe, with a low risk of harm to the patient if performed improperly. This allows the test to be performed in myriad settings outside of traditional clinical laboratories, such as doctors' offices, clinics, substance use treatment facilities, syringe services and outreach programs, and at home. However, unless these tests can be available at low cost, they are unlikely to be widely deployed. Affordability needs to be ensured by capping test costs and providing transparency around pricing.

POC HCV RNA testing has the greatest potential to facilitate a “test and treat” approach to HCV, similar to the current approach to initiating treatment for HIV, using a single-step diagnostic test with immediate treatment initiation [28]. “Test and treat” models have been implemented for many infections/diseases and are associated with improved treatment outcomes including HIV [4, 5], influenza [6], Helicobacter pylori infection [7], and human papillomavirus–associated cervical cancer [8]. Further, recent empirical studies outside the US show that POC HCV diagnostics improve linkage to care, shorten the time to treatment initiation, and result in a higher proportion of treatment uptake among PWID [9–12]. In a recent pilot trial, Grebely et al [29] showed an 81% treatment uptake rate among participants engaged in a single-visit “test and treat” intervention conducted at a peer-led syringe services program in Australia. We envision coupling testing with immediate POC treatment in the US. Rapid POC RNA tests should become widely available at a broad range of healthcare and nonhealthcare venues frequented by individuals at risk of HCV infection. Ease of access to testing will ensure that more individuals are tested, especially those who do not regularly access clinical care in traditional settings, such as PWID, people who are unstably housed or experiencing homelessness, and those without access to transportation. A POC RNA testing platform also has much greater potential to be used in clinical settings where HCV testing is not routine, for example in sexual health clinics, substance use disorder treatment programs, mental health facilities, syringe services programs, shelters, and pharmacies (Figure 1). The imperative is to take the test to the patient, so that diagnosis of HCV infection can be done at the “point of contact,” rather than the traditional “point of care.”

Figure 1.

Illustration of the range of locations where point-of-care hepatitis C virus diagnostic testing can be conducted.

All of this is feasible. We have witnessed the introduction and widespread uptake of rapid tests for severe acute respiratory syndrome coronavirus 2 infection, commonly referred to as coronavirus disease 2019 (COVID-19), by millions of people [30]. The widespread availability of rapid COVID-19 tests changed the medical testing landscape by making testing faster, more accessible, and less expensive. Rapid COVID-19 testing was successfully conducted in homes, airports, offices, and parking lots, among a range of locations never previously considered as sites for diagnosis of a serious infectious disease, and vastly increased the number of people who could be tested. Most of these POC COVID-19 tests produce results in just a matter of minutes—much faster than traditional laboratory tests that can take several hours or even days—and that has allowed for quicker identification of cases that is critical for controlling the spread of the virus, initiating treatment, and improving survival. Rapid COVID-19 tests are also considerably less expensive than traditional laboratory tests, which broadens accessibility to uninsured or underinsured individuals who may not otherwise have had access to testing. Moreover, these rapid, CLIA-waived POC COVID-19 tests can be used privately and self-testing has been widespread, not only increasing detection of infection, but also increasing user health literacy. These same innovations now need to be incorporated into the diagnosis of HCV infection and made widely available.

WHAT IS WORKING

There are several POC HCV RNA diagnostic tests that have excellent performance characteristics in various settings and populations, and the WHO now recommends using POC HCV viral load assays as a strategy to promote access to confirmatory viral load testing and treatment [31]. Despite meeting standards for POC internationally [32], these tests are not currently FDA approved. In their excellent review, Tang et al [31] discuss multiple platforms, including diagnostic accuracy (sensitivity and specificity), types of samples used (fingerstick capillary whole blood, venous whole blood, serum, and plasma), sample volumes needed, and manufacturers' reported limits of detection. Below and in Table 1 we highlight commercially available POC HCV RNA tests identified in that review that are particularly relevant to this article's goal of highlighting tests that can be used to advance diagnosis of current HCV infection in nonclinical settings.

Table 1.

Point-of-Care Hepatitis C Virus Tests Currently Available

Product Name	Manufacturer and Location	Perfomance	Sample Type
Xpert HCV Viral Load Fingerstick assay	Cepheid, Sunnyvale, California	Sensitivity: 99% Specificity: 100%	Capillary blood
Xpert HCV Viral Load assay	Cepheid, Sunnyvale, California	Sensitivity: 98% Specificity: 100%	Plasma
Genedrive HCV ID Kit	Genedrive Diagnostics Ltd, Manchester, UK	Sensitivity: 98% Specificity: 100%	Plasma
TrueNAT HCV RNA assay	Molbio Diagnostics, Goa, India	Sensitivity: 95% Specificity: 99%	Serum, plasma, whole blood
SAMBA II HCV Qualitative Whole Blood test	Diagnostics for the New World, Birmingham, UK	Sensitivity: 96% Specificity: 100%	Whole blood

Abbreviations: HCV, hepatitis C virus; UK, United Kingdom.

The Xpert HCV Viral Load Fingerstick assay and the Xpert HCV Viral Load assay (Cepheid, Sunnyvale, California) both enable diagnosis of active infection by detecting HCV RNA in 1 hour and have a pooled sensitivity and specificity of 98% and 100%, respectively. The test has been used in multiple research and programmatic studies globally [31], including in Australia [33–36], Tanzania [37], Spain [38], Italy [39], Switzerland [40], France [41], Indonesia [42], and Cambodia [43]. Although the Cepheid platform is already used in the US for the diagnosis of other infections [44], this test is not yet FDA approved. The Genedrive HCV ID Kit (Genedrive Diagnostics, Manchester, United Kingdom) detects HCV RNA in 90 minutes using a small volume of plasma (30 μL) [45, 46]. It has been tested in low-resource settings including the countries of Cameroon, Georgia, and India. The TrueNAT HCV RNA assay (Molbio Diagnostics, Goa, India) [45, 46] has pooled sensitivity and specificity reported at 95% and 99%, respectively [31]. The SAMBA II HCV Qualitative Whole Blood test (Diagnostics for the New World, Birmingham, United Kingdom), tested in Ukraine reported a 96% sensitivity and 100% specificity [47]. Overall, the diagnostic accuracy of all these POC tests was consistently high across sample types and varied clinical settings and populations, demonstrating reliable and convenient performance and high potential for widespread implementation and utility in nonclinical settings.

WHAT IS NEEDED

FDA approval is needed for POC HCV RNA on fingerstick blood. The recent FDA reclassification of some HCV diagnostic tests from class III to class II [48] is an important step in this direction. This reclassification will allow POC HCV test manufacturers to use FDA's 510(k) pathway to bring moderate-risk medical devices to market by demonstrating substantial equivalence to a marketed device and is less rigorous than the Premarket Approval pathway required for high-risk devices. FDA approval will enable these RNA POC tests to gain access to the US market and will facilitate reimbursement for use of the testing platforms.

Other potential advances that can facilitate and potentially increase HCV testing include blood collection methods that do not require a venous blood draw or laboratory visit, such as dried blood spots and self-collection devices like TASSO (Tasso, Inc, Seattle, Washington) [49]. The disadvantage of these technologies is that the samples are generally sent to a laboratory for analysis, so immediate results are not available. However, there is evidence, at least for anti-HCV, that self-testing is acceptable [48] and associated with higher uptake of testing, with increased linkage to care relative to standard methods [49]. Regardless of whether individuals can access POC testing or remote testing of self-collected specimens, they will still need access to providers who can initiate treatment and provide follow-up, including physicians, advanced practice providers (ie, nurse practitioners, physician assistants) and/or clinical pharmacists.

Awareness is also needed to increase knowledge of the availability and benefits of HCV testing and treatment among both providers and the general population. There is an urgent need to facilitate widespread testing in both traditional health systems and nontraditional sites where testing and treatment can be at point of contact (Figure 1) to facilitate “test and treat” models for high-risk and hard-to-reach populations. Community support and political will are needed to advance HCV health equity goals [21, 50]. Eliminating isolated anti-HCV testing by hospitals, health departments, and commercial laboratories is important to advance our understanding of the community burden of chronic HCV infection. Moreover, anti-HCV testing does not provide an actionable result to healthcare providers, as a positive test merely requires additional testing. All of these actions have potential to reduce stigma and misinformation, and importantly, to focus a public health approach to HCV testing, diagnosis, and treatment, especially for PWID who are the reservoir for HCV in the US and elsewhere. The elimination of HCV will require many tools and strategies, and although no single product or testing mechanism will reach all affected populations, diagnostic tools that advance the detection of current HCV infection, especially in outreach and other nonclinical settings, have the potential to significantly influence the trajectory of HCV elimination in the US.

Notes

Acknowledgments. We acknowledge the contributions of Dr Lynn Taylor, MD (CODAC Behavioral Healthcare, University of Rhode Island), Ms Collen Flanagan, RN, MS (New York State Department of Health), and Dr Marty Soehnlen, PhD, MPH (Michigan Public Health Laboratory), who were co-presenters at the Association of Public Health Laboratories and Centers for Disease Control and Prevention meeting “Identifying High-Priority Diagnostic Approaches for Advancing Hepatitis C Elimination in the US.”

Disclaimer. The views and conclusions do not necessarily reflect the official position of the funding agencies or the authors' affiliated institutions. Funding agencies did not participate in article preparation.

Financial support. J. F. receives support from the following grants: (grant numbers 1R01DA054703, 7DP1DA048570, and U54GM104942). K. P. acknowledges the support of the University of New Mexico Clinical and Translational Sciences Center (grant number UL1TR001449).

Supplement sponsorship. This article appears as part of the supplement “Towards a Single-Step Diagnosis of Hepatitis C Virus Infection,” sponsored by the Centers for Disease Control and Prevention.