Hepatitis C epidemiology in Switzerland: Our position on new estimates

Recently, a a new paper on the subject of hepatitis C prevalence in Switzerland (1) was published in the Journal of Viral Hepatology. We think that this publication has many limitations, see also «Detailed List of Concerns» in the download section. Together with international experts we have drafted a statement, which we also published as a Letter to the Editor (2) in the same journal:

Dear Editors,

We studied with great interest the above-mentioned publication, which explores the important question about the current prevalence of chronic hepatitis C virus (HCV) infection in Switzerland. Based on their findings, the authors conclude that the prevalence is much lower than estimated in previous studies.

However, we would like to challenge this conclusion as we perceive some inconsistencies.

First, the retrieved publications were not systematically discussed in terms of their validity and reliability. One example of many is the publication by Djebali-Trabelsi (3). This study has a self-declared selection bias and its findings are therefore not generalizable, a limitation not discussed.

Furthermore, the calculations in the different population groups rely on debatable and untraceable assumptions. Repeatedly references are made to secondary rather than primary literature sources. Examples include the percentage of tested and treated in certain population groups, the spontaneous clearance rate or the mortality. Moreover, the authors’ claim that most deaths are due to comorbidities and not HCV in the group of people who inject drugs (PWID) is not underpinned by calculations and contradicts other publications (4).

No stratification is performed even when populations and time periods vary to a great extent as is the case for the prevalence in the general population. These are based on 10 publications where a total of 64 viraemic cases are detected with mostly unclear denominators. The authors then calculate the average prevalence rate and apply it to a population size of 6 million.

Moreover, in the prevalence estimation among individuals from Italy, those with birth years after 1953 were excluded despite a broad birth year distribution of HCV positive persons in Italy (5). The authors also fail to consider other foreign-born individuals from mid-high prevalence countries, which constitute a relevant proportion of Swiss residents (6), consequently raising the probability of underestimating the prevalence.

Additionally, the authors extrapolate data from the SAMMSU cohort. This cohort has an enrollment bias towards PWID under best practice HCV care, which is not discussed by the authors (7). Extrapolating this data to the entire PWID population importantly underestimates viraemia in this group.

In our opinion, the authors discuss limitations unsatisfactorily and handle uncertainties not in accordance to scientific standards. Therefore, we cannot share the authors’ conclusion that prevalence estimates should be revised, and that Switzerland has reached the WHO elimination targets. Further research and production of primary data would be needed to fill this gap.

References
1. Bertisch B, Schaetti C, Schmid P, et al. Chronic hepatitis C virus infections in Switzerland in 2020: lower than expected and suggesting achievement of WHO elimination targets. J Viral Hepat. 2023; 30(8): 667-684.
2. Blach S, Bregenzer A, Bruggmann P, Cerny A, Maeschli B, Müllhaupt B, et al. Assessing the hepatitis C epidemiology in Switzerland: it’s not that trivial. J Viral Hepat. 2023;00:1-2.
3. Djebali-Trabelsi A, Marot A, André C, Deltenre P. Large-scale screening is not useful for identifying individuals with hepatitis B or C virus infection: A prospective Swiss study. J Viral Hepat. 2021;28(12):1756-8.
4. Rüeger S, Bochud P, Dufour J, Müllhaupt B, Semela D, Heim MH, et al. Impact of common risk factors of fibrosis progression in chronic hepatitis C. Gut 2015;64:1605-1615.
5. Kondili LA, Gamkrelidze I, Blach S, Marcellusi A, Galli M, Petta S, et al. Optimization of hepatitis C virus screening strategies by birth cohort in Italy. Liver Int. 2020;40(7):1545-55.
6. Bihl F, Bruggmann P, Castro Batänjer E, Dufour JF, Lavanchy D, Müllhaupt B, et al. HCV disease burden and population segments in Switzerland. Liver Int. 2022;42(2):330-9.
7. Bregenzer A, Conen A, Knuchel J, Friedl A, Eigenmann F, Naf M, et al. Management of hepatitis C in decentralised versus centralised drug substitution programmes and minimally invasive point-of-care tests to close gaps in the HCV cascade. Swiss Med Wkly. 2017;147:w14544.