Integrated respiratory virus surveillance guidance for the EU/EEA: A framework for surveillance to inform public health action
Executive summary
Integrated respiratory virus surveillance combines information from multiple sources to provide a comprehensive assessment of acute respiratory illness in the population. Effective integrated surveillance should generate information to guide public health actions, such as data interpretation, reporting and communication and prevention and control measures.
This guidance supports the fulfilment of EU legislation which sets the requirements for coordinated surveillance, early warning, and response. It focuses on the routine indicator- and event-based surveillance of respiratory viruses, including influenza viruses, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and Respiratory Syncytial Virus (RSV). Although this guidance does not specifically focus on surveillance of zoonotic influenza viruses or overall pandemic preparedness, its implementation will support and strengthen both areas. The guidance defines action-oriented surveillance objectives; the mix and design of surveillance systems needed to meet them, and how the resulting data are analysed to inform action at different levels. Its development was informed by a working group of members of the European Respiratory Viruses Network (ERVI-NET). This guidance is also intended to support national and subnational public health authorities in decisions concerning the allocation of resources for surveillance.
Three overarching objectives guide integrated respiratory virus surveillance in the European Union/European Economic Area (EU/EEA):
- Monitor epidemiological characteristics in time, person and place of acute respiratory illness due to influenza viruses, SARS-CoV-2, RSV and other respiratory pathogens to detect changes that can inform national and EU-level prevention and control measures.
- Monitor virological changes and characteristics of circulating and emerging influenza, SARS-CoV-2 and RSV viruses to detect changes that can inform national and EU-level prevention and control measures.
- Assess the burden of disease and the effectiveness and impact of interventions against acute respiratory illness due to influenza viruses, SARS-CoV-2, RSV and other respiratory pathogens.
Objectives 1 and 2 describe timely, continuous epidemiological monitoring and virus characterisation, which is the foundation of routine respiratory virus surveillance. Objective 3 describes key areas where surveillance data can be used for studies to contribute evidence to guide the investment and targeting of interventions. Sub-objectives provide a more complete description of the purpose and scope of each objective. The sub-objectives are broken down into the information required from surveillance to inform action.
This framework provides the foundation for identifying the most appropriate mix of surveillance systems required to fully meet the objectives. Design aspects are also outlined for systems that are fit for purpose and sustainable. National or subnational public health authorities should map the data sources available to them to understand gaps and opportunities.
Core surveillance systems should be prioritised for routine epidemiological monitoring and virus characterisation. They include surveillance in primary care and hospitals, virus characterisation, laboratory-based surveillance and event-based surveillance. When used together, core systems can complement one another to meet many of the surveillance objectives:
- Well-designed systems based on the influenza-like illness (ILI), acute respiratory infection (ARI) and severe acute respiratory infection (SARI) syndromic case definitions with integrated virological testing remain the principal approach for integrated respiratory virus surveillance.
- Hospital-based surveillance is central to understanding severity and impact and cannot be readily replaced by other systems. Surveillance that is based on the SARI syndromic case definition with integrated virological testing is preferred over laboratory-confirmed hospital surveillance since it can contribute more fully to both epidemiological and virus characterisation objectives.
- National or subnational capacity for routine genomic virus characterisation is required to meet Objective 2. Where countries do not have capacity for phenotypic characterisation, selected specimens can be sent using established supranational mechanisms.
- Case-based data, particularly for severe disease, are required at national/subnational and EU/EEA levels to facilitate the advanced analyses needed to fully meet the surveillance objectives, including estimation of risk factors, burden and evaluation of interventions. Data linkage, ideally across the clinical care spectrum, is essential to ensure completeness of key variables, and assess severity, clinical outcomes and the impact of interventions.
Supplementary surveillance systems provide additional information not captured by core systems, covering different populations and more of the surveillance pyramid. They can be selected to address weaknesses or gaps in core systems and to ensure adequate coverage across the surveillance pyramid. Examples commonly used in the EU/EEA include mortality monitoring, monitoring of outbreaks in specific settings, wastewater-based and participatory surveillance.
Complementary data sources provide information that is vital for strengthening public health decision-making but since these sources are often beyond the organisational remit of respiratory virus surveillance teams, they are considered outside of routine surveillance. They include hospital occupancy monitoring, data on vaccine coverage, drivers of vaccine hesitancy and pharmaceutical usage data.
It is important to maintain the ability to detect signals, monitor the impact on healthcare and characterise circulating viruses at any time of the year through indicator- and event-based surveillance. SARS-CoV-2 has not become a seasonal winter virus and out-of-season epidemics of RSV and influenza viruses can occur. Similarly, influenza viruses detected during the summer can support early assessments of the coming winter season and may provide a signal of zoonotic non-seasonal virus transmission. Year-round, consistent data also supports the setting of thresholds, analysis and signal detection. Where resources are limited, surveillance in the summer should, at a minimum, allow for detection, assessment and communication of epidemiological and virological signals, with the option to scale up, as required.
The optimal combination and design of surveillance systems is context-specific and can evolve over time. It may be necessary to periodically review and adapt the mix of surveillance systems, taking into consideration new technologies and developments, especially as the use of electronic health data continues to expand and emerging AI applications reshape public health surveillance. Reductions in human and financial resources available for surveillance may also affect which systems can run and how well they are maintained.
Ensuring the quality and readiness of respiratory virus surveillance is an ongoing, cyclical process to assess whether surveillance systems can continue to meet their objectives under routine conditions and in periods of increased threat. Monitoring and evaluation, preparedness planning, collaboration and exchange all support this process, ensuring that surveillance systems can adapt to changes, while maintaining robustness, comparability, and sustainability.
Integrated respiratory virus surveillance guidance for the EU/EEA - A framework for surveillance to inform public health action
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