The importance of reporting notifiable infectious diseases – the Swiss reporting system

Introduction

In medicine, assessing, diagnosing and treating a patient follows a structured process: gather patient history, perform diagnostics, form a diagnosis, prescribe the appropriate treatment and monitor outcomes. Epidemiology follows the same logic – just at a population level. Reporting is the crux of the collaboration between a clinician and an epidemiologist. It is the link between the conclusion of the clinician’s process and the beginning of the epidemiologist’s. At its core, epidemiology is medicine on a larger scale. Recognising these parallels can help strengthen collaboration between clinicians and epidemiologists – because whether treating one or many, the goal remains the same: better health for all [1].

Since the COVID-19 pandemic, a decline in compliance with reporting of infectious diseases in humans has been observed. Missing reports from the clinical or laboratory side hampers case assessment and classification. This in turn leads to biased conclusions at the population level and, at its extreme, to poorly targeted public health measures. Without consistent and complete reporting, emerging trends and threats can go unnoticed until they spiral out of control, delaying interventions that could prevent further illness and save lives.

The present article provides an overview of the mandatory reporting system in Switzerland, highlighting the importance and applications of the reporting mandate, through various real-world examples.

Swiss reporting system

The obligation to report is a central element of systems of national surveillance of infectious diseases worldwide. In Switzerland, it is realised in close collaboration between the Federal Office of Public Health (FOPH), the Cantonal Medical Services, laboratories and physicians. The Ordinance on the reporting of observations of communicable diseases in humans [2] determines reporting criteria, deadlines and channels for communicable disease notification. Included in the Ordinance are particularly severe diseases (such as haemorrhagic fevers), diseases requiring immediate control measures (such as measles and meningococcus) as well as diseases with outbreak potential (such as salmonella and listeriosis) but also diseases with an ongoing endemic activity that are preventable such as vaccine-preventable or sexually transmitted diseases – see figure 1 for the full list. The Ordinance is reviewed regularly and changes made are based on the national public health situation, as well as current epidemiological and international developments. It is through such a review that in 2016 Zika virus infections became mandatory to report, and in 2020 vancomycin-resistant enterococci (VRE) outbreaks in hospitals as well as COVID-19 were added. Most recently, “extraordinary epidemiological observations in hospitals” was added to the reporting mandate. The trigger was the multiresistant fungus Candida auris, which has a high epidemic potential.

The guiding principle “whoever diagnoses, reports” (with few exceptions) applies to physicians, hospitals, laboratories, public and private health institutions and requires them to report infectious disease cases. The Reporting Obligation Guidelines [3] define specific reporting criteria and deadlines as well as particularities of various pathogens (tables 1 and 2). These reporting criteria are based on best current practice and the Swiss Society for Infectious Diseases guidelines [4]. All cases meeting the reporting criteria – most often a positive laboratory result – must be submitted within 2 hours, 24 hours or 1 week, depending on the pathogen. Just as timely treatment is essential for patient health outcomes, timely case reporting is crucial for effective public health response. For example, during outbreaks, early case notifications have allowed for rapid containment measures, such as isolating cases or issuing targeted public health warnings.

Clinicians report clinical findings using specified forms that contain information about the person concerned, laboratory diagnostics, exposure and vaccination status. Depending on the reporting deadline, these clinical reports can be submitted by post or via HIN Mail (a secure electronic communications system used in the Swiss medical field) – reports via telephone can be made only in cases where (suspicion of) pathogens with a 2-hour reporting mandate are involved. In the case of tuberculosis, measles and congenital rubella, additional information must be provided in a supplementary report. Laboratories report their laboratory findings using the appropriate forms, which include information on the person concerned, the referring physician, the date of sampling and testing, the test method and the result. All reports from labs are received digitally only since January 2024.

Data processing and analysis

All reports are compiled in a national database. Cantonal authorities have access to their cantonal data and can exchange with the FOPH in real time. After a plausibility and completeness check, reports from laboratories and physicians are consolidated into a single case and classified according to standard case definitions as “Confirmed”, “Probable”, “Possible” or “Not a case”. The case definitions are developed and maintained in line with other international case definitions and classification criteria such as the European Centre for Disease Prevention and Control (ECDC) Case Definitions [5]. These form part of the Reporting Obligation Guidelines [2], which are updated annually by the authors of the present article in collaboration with colleagues from the department of infectious diseases at the FOPH. Final case evaluation typically requires both laboratory and clinical findings (see tables 3 and 4). If either of these is missing, correct classification is at risk, potentially causing under- or overestimation of case numbers.

Following data evaluation, individual measures may be necessary, depending on the pathogen. These are described in more detail in the “Data usage” chapter.

Reporting data are regularly published by the FOPH on the infectious diseases dashboard (IDD) [6]. Here, interested parties can interactively access basic information on current incidences and trends in infectious diseases.

In addition, in-depth epidemiological data analyses are performed and delivered to supranational institutions such as the WHO or are published on the FOPH website or in peer-reviewed journals.

Low reporting compliance and data quality of clinical reports

Figure 2 visualises the proportion of missing clinical reports relative to the total number of reports received for individual pathogens. Relative changes in the proportion of missing reports between pathogens were calculated as $({\mathrm{proportion}}_{\mathrm{Covid}}-{\mathrm{proportion}}_{\mathrm{Pre}-\mathrm{Covid}})/{\mathrm{proportion}}_{\mathrm{Pre}-\mathrm{Covid}}$ to compare differences in reporting completeness across pathogens. Figure 2 reveals that the proportion of missing clinical reports is high, and has increased again since the SARS-CoV-2 pandemic. In the period 2016–2019, 7–16% of clinical reports, depending on the pathogen, were missing; this figure increased to 8–30% in 2020–2023. Overall, the proportion of missing clinical reports has increased 2.3-fold since the COVID-19 pandemic. In addition, the reports received are often lacking critical information. Gaps in reporting do not only affect surveillance – they delay evidence-based policymaking that could directly benefit both clinicians and patients in the long run.

Presumed reasons why clinicians fail to comply with their reporting obligations include not only the anticipated effort involved, but also a lack of knowledge about which diseases and situations require reporting and how to report them. Similarly, limited knowledge on the utility of these reports can reduce motivation to make the effort.

Why it is worthwhile reporting

Reporting detects and helps mitigate outbreaks

The FOPH runs a weekly statistical outbreak investigation to evaluate whether reported case numbers exceed the expected values (fig. 3). If the expected threshold is surpassed, the case numbers are examined in more detail – checking age, sex, domicile and, if relevant, type or species.

In case of a signal, further investigation is initiated to evaluate whether or not an outbreak can be confirmed. Whole-genome sequencing, for example, is conducted by the reference laboratories to detect clusters and in the best case establish a link to a potential common source in the case of foodborne diseases. When clusters are detected, the goal is to identify and eliminate the source as quickly as possible, thus avoiding further spread of cases. Clinical reports provide valuable information about potential sources of infection and enable measures to be taken quickly.

Example: Listeria outbreak in 2022

At the beginning of July 2022, an unusually high number of listeriosis cases were reported to the FOPH. Whole-genome sequencing confirmed that the cases formed a cluster (20 patients). On behalf of the FOPH, the patients were routinely interviewed by the Competence Center for Epidemiological Investigations (KEA) at the Swiss Tropical and Public Health Institute in Basel (Swiss TPH). This survey revealed that the source could be smoked trout from a specific farm. During the subsequent inspection, the competent food enforcement authority detected listeria in the smoked fish and in the production environment. Whole-genome sequencing enabled the food samples to be linked to the outbreak cluster, confirming them as the cause of the outbreak. The products were recalled and the Federal Food Safety and Veterinary Office issued a public warning. Production was temporarily suspended. The cause of the contamination was identified and remedied [10].

Data sharing statement

The data used in this study were derived primarily from publicly available sources and published studies, as cited in the article. These data can be accessed through the original sources indicated in the references.

The non-public data used for this analysis are held by governmental public health authority and may contain sensitive information. For this reason, and in accordance with applicable data protection requirements and governmental obligations to protect privacy, these data will not be deposited in an open data repository. Data may be made available upon reasonable request. Requests should be directed to the corresponding author and will be assessed on a case-by-case basis.