Modelling the impact of different testing strategies for HCV infection in Switzerland

Hepatitis C prevalence and cascade of care among patients in the decentralised opioid agonist therapy programme of the canton of St Gallen, Switzerland: a cross-sectional study

BACKGROUND

To eliminate chronic hepatitis C virus (HCV) infection by 2030, 90% of those infected must be diagnosed and 80% treated. In Switzerland, >40% of the estimated 32,000 infected people are still undiagnosed. In the canton of St Gallen, HCV prevalence and cascade of care have only been studied in the centralised opioid agonist therapy (OAT) setting (institutions), although about 80% of OAT patients are treated decentrally (general practitioner [GP] or pharmacy).

AIM

To describe HCV prevalence and cascade of care among patients in the decentralised OAT programme of the canton of St Gallen, Switzerland, and compare it to contemporaneous data from the centralised setting.

METHODS

For each patient receiving his/her OAT from a GP or pharmacy on 1 April 2021, the cantonal medical office sent a questionnaire to the prescribing GP. Patient characteristics, HCV antibody (Ab)/RNA screening uptake, HCV Ab/RNA prevalence and HCV treatment uptake were obtained and compared to those of patients of the Medizinisch-soziale Hilfsstelle 1 in St Gallen (centralised setting).

RESULTS

Of the 563 OAT patients under the care of 127 GPs, 107 patients from 41 GPs could be analysed (median age: 48 years [IQR: 40-56]; ongoing intravenous drug use: 25%; OAT provider: 66% GP, 34% pharmacy). HCV Ab screening uptake was 68% (73/107) with an HCV Ab prevalence of 68% (50/73) among those tested. Of the HCV Ab-positive patients, 84% (42/50) were HCV RNA-tested, among whom 57% (24/42) were viraemic. HCV treatment uptake was 83% (20/24), with 95% (19/20) achieving a sustained virological response. Non-uptake of HCV screening and treatment tended to be higher among patients receiving OAT at the pharmacy vs at the GP's office: 37% vs 26% (p = 0.245) for screening and 30% vs 7% (p = 0.139) for treatment. The proportion never HCV Ab-tested and the proportion of HCV Ab-positives never HCV RNA-tested was significantly higher in the decentralised compared to the centralised setting: 32% vs 3% (p <0.001) never Ab-tested and 16% vs 0% (p = 0.002) never RNA-tested. In contrast, HCV treatment uptake (83% vs 78%), sustained virological response rate (95% vs 100%) and residual HCV RNA prevalence among the HCV Ab-positive (12% vs 14%) were comparable for both settings.

CONCLUSION

In the decentralised OAT setting of the canton of St Gallen, HCV Ab prevalence is high. Since HCV Ab and RNA screening uptake are markedly lower than in the centralised setting, potentially >40% of patients with chronic HCV are not diagnosed yet. HCV screening in the decentralised setting needs improvement, e.g. by increasing awareness and simplifying testing. High HCV treatment uptake and cure rates are possible in centralised and decentralised settings.

Impact of voluntary testing on infectious disease epidemiology: A game theoretic approach

The World Health Organization recommends test-and-treat interventions to curb and even eliminate epidemics of HIV, viral hepatitis, and sexually transmitted infections (e.g., chlamydia, gonorrhea, syphilis and trichomoniasis). Epidemic models show these goals are achievable, provided the participation of individuals in test-and-treat interventions is sufficiently high. We combine epidemic models and game theoretic models to describe individual's decisions to get tested for infectious diseases within certain epidemiological contexts, and, implicitly, their voluntary participation to test-and-treat interventions. We develop three hybrid models, to discuss interventions against HIV, HCV, and sexually transmitted infections, and the potential behavioral response from the target population. Our findings are similar across diseases. Particularly, individuals use three distinct behavioral patterns relative to testing, based on their perceived costs for testing, besides the payoff for discovering their disease status. Firstly, if the cost of testing is too high, then individuals refrain from voluntary testing and get tested only if they are symptomatic. Secondly, if the cost is moderate, some individuals will test voluntarily, starting treatment if needed. Hence, the spread of the disease declines and the disease epidemiology is mitigated. Thirdly, the most beneficial testing behavior takes place as individuals perceive a per-test payoff that surpasses a certain threshold, every time they get tested. Consequently, individuals achieve high voluntary testing rates, which may result in the elimination of the epidemic, albeit on temporary basis. Trials and studies have attained different levels of participation and testing rates. To increase testing rates, they should provide each eligible individual with a payoff, above a given threshold, each time the individual tests voluntarily.

Hepatitis C core antigen test as an alternative for diagnosing HCV infection: mathematical model and cost-effectiveness analysis

BACKGROUND

The cost and complexity of the polymerase chain reaction (PCR) test are barriers to diagnosis and treatment of hepatitis C virus (HCV) infection. We investigated the cost-effectiveness of testing strategies using antigen instead of PCR testing.

METHODS

We developed a mathematical model for HCV to estimate the number of diagnoses and cases of liver disease. We compared the following testing strategies: antibody test followed by PCR in case of positive antibody (baseline strategy); antibody test followed by HCV-antigen test (antibody-antigen); antigen test alone; PCR test alone. We conducted cost-effectiveness analyses considering either the costs of HCV testing of infected and uninfected individuals alone (A1), HCV testing and liver-related complications (A2), or all costs including HCV treatment (A3). The model was parameterized for the country of Georgia. We conducted several sensitivity analyses.

RESULTS

The baseline scenario could detect 89% of infected individuals. Antibody-antigen detected 86% and antigen alone 88% of infected individuals. PCR testing alone detected 91% of the infected individuals: the remaining 9% either died or spontaneously recovered before testing. In analysis A1, the baseline strategy was not essentially more expensive than antibody-antigen. In analysis A2, strategies using PCR became cheaper than antigen-based strategies. In analysis A3, antibody-antigen was again the cheapest strategy, followed by the baseline strategy, and PCR testing alone.

CONCLUSIONS

Antigen testing, either following a positive antibody test or alone, performed almost as well as the current practice of HCV testing. The cost-effectiveness of these strategies depends on the inclusion of treatment costs.