Testing strategies for SARS-CoV-2
The implementation of objective-driven and sustainable testing strategies for COVID‑19 supports the overall public health response to the pandemic and helps mitigate its impact on vulnerable populations and healthcare systems, while ensuring that societies and economies can continue to function as described in the document on COVID-19 testing strategies and objectives.
ECDC proposes five main objectives for testing:
- to control transmission;
- to monitor SARS-CoV-2 transmission rates and severity;
- to mitigate the impact of COVID-19 in healthcare and social care settings;
- to detect clusters or outbreaks in specific settings;
- to maintain COVID-19 elimination status once achieved.
Ideally, all people with COVID-19 symptoms should be tested as soon as possible after symptom onset. When this is not possible, testing should be done according to a clear sampling strategy that allows for representative and reliable surveillance data.
Test result turnaround time should be minimised, people testing positive should be isolated and timely contact tracing and testing of all close contacts, irrespective of symptoms, should be carried out.
During the influenza season, all patients with acute respiratory symptoms in hospitals and within other healthcare settings, and all specimens (or a representative sample of them if resources for comprehensive testing are not available) from sentinel primary care surveillance, should be tested for SARS-CoV-2 and seasonal influenza in parallel, to monitor incidence and trends over time and to inform response measures in a consistent manner.
Healthcare and social care settings require periodic and comprehensive testing of all staff and residents/patients. All patients/residents should also be tested at or just prior to admission during community transmission.
Testing policies and systems should be in place for rapid detection and control of clusters or outbreaks in certain settings in order to protect the populations present there, and to protect the community from amplified transmission.
Countries experiencing high SARS-CoV-2 transmission in a localised area could consider testing the whole population of the affected area to identify cases, to isolate them and interrupt the chains of transmission.
Countries or subnational areas that achieved sustained control of the circulation of SARS-CoV-2 should, in addition to quarantine, consider targeted testing and follow up of individuals coming from other areas or countries that have not yet achieved sustained virus elimination status.
Member States should adapt these recommendations based on the national/local epidemiological situation and their resources, ensuring that testing also covers surveillance needs.
Genomic surveillance of SARS-CoV-2 is essential to detect, monitor and assess virus variants that can result in increased transmissibility, disease severity, or have other adverse effects on public health and social control measures. Obtaining timely and accurate information on the emergence and circulation of variants of concern (VOCs) and variants of interest (VOIs) requires robust surveillance systems, including integrated genome sequencing with a well-defined sampling and sequencing strategy to ensure representativeness and reliability of findings.
ECDC has published a practical guidance to EU/EEA Member States on implementing genomic SARS-CoV-2 surveillance, including advice on the number of samples that need to be sequenced to achieve various objectives.
For genomic surveillance of SARS-CoV-2, ECDC recommends two complementary sampling approaches:
- representative sampling of SARS-CoV-2 RT-PCR positive cases from existing, population-based surveillance systems;
- targeted sampling of SARS-CoV-2 positive cases occurring in special settings or populations.