The Prevalence of Cystic Fibrosis—a Comparison of Patient Registry Data and Billing Data Within the German Statutory Health Insurance System

Prevalence estimates are important in the context of healthcare planning for rare diseases such as cystic fibrosis (1). This study aims to estimate on the basis of administrative data the prevalence of persons with cystic fibrosis in 2019 in Germany on the basis of outpatient billing within Germany’s statutory health insurance system and registry data of the German Cystic Fibrosis Registry (2).

Methods

The study is based on nationwide and outpatient billing data across all health insurers for all 73,052,555 million members of the statutory health insurance system (3) who accessed healthcare services during the observation period (1 January 2019 to 31 December 2020) (data status 15 January 2022). We included pseudonymized, member-related information regarding billed services and diagnoses. Persons with cystic fibrosis were defined on the basis of the diagnoses made by statutory health insurance physicians (E84, P75 according to the ICD-10). The study population consisted of all persons in whom during the study period in 2019 a confirmed diagnosis of cystic fibrosis was coded in at least one quarter (index quarter) and a further confirmed diagnosis of cystic fibrosis was documented in the follow-up period (index quarter plus three following quarters—M2Q criterion). This approach ensured that persons in whom a diagnosis was made once or only as a suspected diagnosis were not included. Data from private health insurers (10.5% of the total population of Germany in 2019) were not available because of lacking ICD codes and insufficient operationalization by means of medications. To estimate privately insured persons among persons with cystic fibrosis or persons with cystic fibrosis who had not consented to being included in the registry, institutions participating in the registry were surveyed; 58 institutions including 5779 persons with cystic fibrosis participated (September 2023). The German Cystic Fibrosis Registry has been run by the German Cystic Fibrosis Association since 1995 and collects diagnostic and annual disease progression data from persons with cystic fibrosis who consented to having their data processed from participating centers (2019: 86) (2). Central pseudonymization and queries interrogating the population register minimized duplicates and loss to follow-up. The selected study population included persons with cystic fibrosis who were diagnosed before or in 2019 and who presented to a participating institution either in 2019 or in the following years or for whom proof of life was obtained from the population register (data status 4 August 2023). For the available data we calculated the administrative 1-year prevalence. This was calculated as the ratio of the number of persons with cystic fibrosis and the total population of the Federal Republic of Germany on 31 December 2019 (87,166,711 million population) (4) per 10,000 head of population.

Results

According to data from the statutory healthcare insurance system, 7876 persons with cystic fibrosis were living in Germany in 2019; they were either members of statutory health insurance schemes and/or were included in the German Cystic Fibrosis Registry (including 779 persons with cystic fibrosis for whom no annual disease progression data were available). When we extrapolated the numbers for the overall total population, for a proportion of 5.8% with private health insurance (<18 years 7.6%; ≥18 years 4.5%; survey), 8333 persons with cystic fibrosis and for a proportion of 4.5%, 7576 persons with cystic fibrosis (survey) did not consent to being included in the registry. The prevalence estimate based on administrative data for cystic fibrosis in Germany in 2019 is 0.947 in every 10,000 members of statutory health insurance schemes and 1.002 in every 10,000 head of population (German Cystic Fibrosis Registry). The age distribution from both datasets shows very good agreement up to age 50 years (Figure). The proportion of adults in the total cohorts is 65.1% (5131/7876; data from the statutory health insurance system) and 61.6% (4466/7250; data from the German Cystic Fibrosis Registry). The group older than 50 is notably more strongly represented in the data from the statutory health insurance system (1045 persons with cystic fibrosis—13.3% of the total cohort) than from the registry (395—5.2%).

Figure

Age group dependent prevalence of persons with cystic fibrosis in Germany based on billing data from statutory health insurance physicians and the German Cystic Fibrosis Registry in 2019

Discussion

The prevalence estimate based on administrative data in Germany shows numbers of persons with cystic fibrosis between 7576 (German Cystic Fibrosis Registry) and 8333 (National Association of Statutory Health Insurance Physicians) in 2019, with good agreement until age 50. This prevalence estimate—0.911 (registry) and 1.002 (statutory health insurance data) per 10,000—is higher than estimates from 2004 (0.829/10,000 population). In 2004 Germany was at a similar level to Austria (0.839), the Netherlands (0.781), and France (0.750) (5). The increase in the estimated prevalence is the consequence of the improved probability of survival in association with causal treatments for cystic fibrosis and is not due to migration or neonatal screening; the effects in terms of health economics cannot be assessed to date. Selection bias in those older than 40 years as a consequence of the higher proportion of persons with cystic fibrosis with genetic variants with improved residual function will be reduced as a result of causal therapies (2). Prevalence estimates based on administrative data are subject to methodological limitations. Registry data are characterized by valid capture of the diagnostic criteria and disease specific relevant data on disease course and treatment, as well as by a great willingness to participate. Obstacles relating to data protection, consent, funding, data documentation, linking up with population register data, death registers, or transplant registries and promoting voluntary participation in affected persons and participating institutions can affect the completeness of the data. Risk adapted contribution rates lower the proportion of privately insured people among persons with cystic fibrosis—especially in adults. Outpatient billing data form the basis for a substance and medicine based, and transparently explained, cohort formation and prevalence estimates that are as valid as possible on the basis of the population of all members of statutory health insurance members who—across health insurers and regions—access outpatient care across the board. Health service data collected for billing purposes and not for research can—in terms of confirming the diagnosis and quality of the documentation—not be compared with research data and tend to be overestimates. The discrepancy in the over-50s may be a consequence of the quality of the documentation or an indication of long-term survivors who are not receiving care in institutions for persons with cystic fibrosis. Cystic fibrosis is a rare condition whose prevalence increases in association with highly effective causal treatments.

Lutz Naehrlich, Christian Gallowitz, Manuel Burkhart, Diana Kurch-Bek

Conflict of interest statement
LN receives financial institutional support from Vertex Pharmaceuticals and from the German Center for Lung Research. He is the medical director of the German Cystic Fibrosis Registry and Pharmacovigilance Study Manager of the European Cystic Fibrosis Society Patient Registry. He receives funding for medical writing from Articulate Science und Complete Health Vizion.

The remaining authors declare that no conflict of interest exists.

Manuscript received on 6 January 2024, revised version accepted on 12 June 2024.

Translated from the original German by Birte Twisselmann, PhD.

Cite this as:
Naehrlich L, Gallowitz C, Burkhart M, Kurch-Bek D: The prevalence of cystic fibrosis—a comparison of patient registry data and billing data within the German statutory health insurance system.
Dtsch Arztebl Int 2024; 121: 712–3. DOI: 10.3238/arztebl.m2024.0126

References

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