The European Centre for Disease Prevention and Control tells HEQ about the role of COVID-19 testing in preventing the spread of the virus.
The European Centre for Disease Prevention and Control (ECDC), the EU-wide agency tasked with co-ordinating Europe’s efforts to combat infectious diseases, has been at the forefront of efforts to arrest the spread of COVID-19 across the continent.
HEQ hears from ECDC about COVID-19 testing, contact tracing and international travel.
How have widespread ‘test and trace’ measures assisted in combating the spread of COVID-19 in EU Member States? What is the significance of cluster testing in regions which have experienced outbreaks of new variants of the virus?
Testing and contact tracing are some of the most important tools we have to combat the epidemic. ECDC recommends widespread, fast testing of everyone with symptoms and people without symptoms in some special settings such as long-term care facilities. Widespread, timely testing allows sick people to be isolated, and for public health authorities to start contact tracing.
ECDC does not collect detailed information on contact tracing operations from EU/EEA Member States, hence ECDC cannot comment specifically on how well testing and tracing operations are implemented in Member States and its relative contribution to reductions in transmission compared to other measures. However, ECDC has published guidance on collecting indicators to evaluate contact tracing activities. Recently, work was initiated to collect data at the EU level. Mathematical modelling studies have been conducted assessing how much transmission can been prevented, but this is different from measuring actual impact in countries. Most modelling studies highlight the importance of speed during contact tracing operations.
In light of the new emerging variants of SARS-CoV-2, cluster testing in regions which have experienced outbreaks of the virus is important in order to identify any potential, newly identified variant that may have increased transmissibility or higher attack rates, or other concerning properties. At least five specimens from each outbreak should be sequenced to identify the variants dominating the outbreak.
The extent to which testing and contact tracing contribute to reducing transmission (or the impact of ‘test and trace’ measures) depends on several factors:
- How widespread testing is: the more testing is done, the more cases are picked up for whom contact tracing can be done
- How fast testing is done – people with symptoms should be tested as soon as possible after they start having symptoms. To achieve this:
O People must be informed that they should seek testing as soon as possible and not wait
O Testing should be easily accessible; that is, it should be close to where people are, and without waiting time
O Laboratories should process tests as soon as possible and return results to the patient and to public health authorities so that they can initiate contact tracing
- How fast contact tracing is done:
O Public health authorities should interview the infected person as soon as possible about whom they have been in contact with
O Public health authorities should get in touch with the relevant contacts as soon as possible to inform them about the need to quarantine
- Compliance with quarantine:
O If people do not comply with quarantine they risk transmitting infection to others
O People may face challenges complying with quarantine if they are in occupations where they are not paid if they do not work and if they cannot work from home
Additionally, it may be difficult for people to quarantine in a safe way in the household and prevent contact with family members. Some countries provide central quarantine facilities, financial support for people who cannot work from home, and services providing food and medicine, with the goal of avoiding people going shopping before starting quarantine or during quarantine, potentially infecting others.
Many countries have also implemented mobile apps to support contact tracing. Mobile apps should only complement, not replace, conventional contact tracing operations. ECDC and the World Health Organization (WHO) will shortly publish joint guidance on how to measure their effectiveness and their added value in complementing conventional contact tracing operations. Because of the privacy-preserving nature of such apps, these evaluations are particularly challenging.
Regarding cluster testing and detection, ECDC recommends enhanced, more extensive contact tracing for cases known or suspected to be infected with variants of concern (VOCs). This includes, for example, testing all contacts (high- and-low risk) rather than just the high-risk contacts. Some Member States have indeed performed more extensive contact tracing around cases suspected to be infected with VOCs, and this may in some cases have included more extensive testing, but ECDC does not have any detailed information on this.
In general, not just for VOCs, ECDC recommends that countries consider so-called ‘backward’ contact tracing with the aim of detecting clusters. This means going back further in time to figure out if there was a larger event that the subject attended and where they may have acquired the infection. ECDC recommends tracing and testing others at the same event to discover possible clusters of symptomatic and asymptomatic cases. Some countries, such as Ireland, already have backward tracing in place.
What are the relative benefits of rapid antigen detection (RADT) and polymerase chain reaction (PCR) COVID-19 tests?
RADTs can contribute to overall COVID-19 testing capacity, offering advantages in terms of shorter turnaround times and reduced costs, especially in situations in which RT-PCR testing capacity is limited. However, the test sensitivity for RADTs is generally lower than for RT-PCR or other nucleic acid amplification technique (NAAT), while the specificity is similar. RADTs perform best in cases with high viral load, in pre-symptomatic and early symptomatic cases up to five days from symptom onset, while RT-PCR can detect the virus for longer, several days or even weeks after the symptom onset and more reliably in asymptomatic patients. RT-PCR may be affected by the mutations of the viral genome, but the laboratories can easily identify those mutations that cause a mismatch via tools like PrimerScan if the primer or probe sequences are known.
Clinical validation studies are needed to assess the potential impact of mutations to the RADT sensitivity. Those RADTs that rely on the nucleocapsid protein, which is more stable, are less likely to be affected by mutations. Unlike RT-PCR, the RADTs are inherently lacking a positive control and therefore one cannot assess if sampling was done properly.
RADTs can be used for self-testing by lay users, while RT-PCR should be performed by trained laboratory personnel. RT-PCR may be used for quantification of the viral RNA load, that can be correlated with infectiousness, while RADTs can be used only in a qualitative manner.
What are the key limitations of saliva as a sample material for COVID-19 testing?
There is heterogeneity in the results regarding the sensitivity of RT-PCR when using saliva as sample type in the available studies, likely due to differences in sampling techniques, sampling times and the type of population being tested. The sample types that contain saliva and the various saliva collection techniques can be very different and yield variable sensitivities. Some saliva collection techniques can also be quite cumbersome. Saliva can be viscous, and this can cause issues with the subsequent RNA extraction methods.
The current limited evidence supports the use of saliva as alternative sample type for use with RT-PCR assays, when the sample collection is performed within five days from symptom onset and the viral load is high. The current limited evidence does not support the use of saliva as an alternative sample material for RADTs due to reduced sensitivity. Further clinical studies are warranted on the sensitivity of saliva as sample material on the different available tests and also for symptomatic and asymptomatic children, and to standardise the sampling collection methods. Commercial diagnostic assays for saliva with a CE marking are available in the EU/EEA, however none of these assays is included in the Health Security Committee’s list of mutually recognised tests.
Should a negative COVID-19 test alone be enough for a person to be considered safe to travel internationally?
Travel measures, such as quarantine and testing of travellers, aim at reducing the likelihood of SARS-CoV-2 transmission prior to, during, and after travel, in order to delay the introduction of the pathogen in new areas or populations. Current evidence supports a combined approach to quarantine and testing of travellers: a pre-departure test (48 hrs pre-departure or test directly upon arrival) combined with quarantine and a further test five to seven days after arrival to release from quarantine if the test is negative.
A single test alone performed before travel could miss the people who are incubating the disease (i.e. in cases where the virus is not detectable via RT-PCR or RADT), and who will potentially develop the disease later. A single test performed on arrival could miss the people who have been infected very close to travelling and can develop the disease in the coming days.
Vaccinated individuals or individuals who have recovered from a laboratory-confirmed SARS-CoV-2 infection within 180 days prior to travel can be exempted from quarantine and testing requirements, although we know that both groups are not fully protected. Therefore, both groups should continue to practise preventive measures, such as wearing a face mask and respecting the need for physical distancing during travel.
How important has cross-border collaboration and support between nations been in developing a response to COVID-19?
Collaboration between countries took place at several levels, from political to operational. Co-ordination of public health measures was facilitated by the European Commission through the Health Security Committee, where ECDC provided advice based on the latest scientific evidence. Together with the WHO Regional Office for Europe, ECDC co-ordinated the European COVID-19 surveillance network, which has been meeting regularly since the beginning of the pandemic. Through this network, European countries exchanged experiences and good practices and agreed on suitable surveillance approaches. COVID-19 response in one country could not be done effectively without access to information and experiences from other countries in the EU and globally. Here ECDC played a significant role carrying out global epidemic intelligence and providing country specific epidemiological overviews based on all data sources available.
European Centre for Disease Prevention and Control
This article is from issue 18 of Health Europa. Click here to get your free subscription today.