Designing a COVID19 Surveillance Testing Program
Posted 10th December 2020
What is Surveillance Testing?
COVID-19 surveillance testing detects and monitors for the occurrence of infection at the population level. By testing groups instead of individuals, you can efficiently monitor populations, ranging from small companies to university campuses. Results from surveillance testing can serve as an early warning of infection and inform targeted interventions that slow the spread.
Surveillance testing is practical for any business looking to reduce the threat of an outbreak. Essential businesses that require on-site workers, such as meat packing plants and manufacturing sites have incorporated surveillance testing into their COVID mitigation plans to enable routine operations to continue safely. Nursing homes are using surveillance testing to detect infection early to protect high-risk groups, who are more prone to transmission and severe illness.
Surveillance testing can be used to:
- Identify asymptomatic/pre-symptomatic infections early and stop group interactions when infection is detected.
- Gauge the effectiveness of current COVID mitigation measures.
- Demonstrate commitment to ensuring employee and customer safety
Picking the Right Surveillance Detection Method
Rapid antigen tests, which have some uses in diagnostic testing, are not beneficial in surveillance due to their low sensitivity and specificity. Their low specificity makes them prone to a high false positive results, especially in low prevalence populations. As disease prevalence decreases, it becomes more difficult for rapid antigen tests to accurately identify an active infection. False positives have significant implications for any business, leading to halting on-site operations, unnecessary employee stress, or inappropriate decisions related to isolation and care.
Rapid antigen tests detect proteins on the surface of the virus, yielding qualitative results that heavily depend on higher viral loads for detection. Compared to RT-qPCR, antigen tests need a sample to contain thousands, or even tens of thousands, of viral particles per microliter to produce a positive result.
Rapid antigen tests also have a 20% false negative rate, meaning they miss 1 out of 5 active COVID infections. Due to their low sensitivity, PHE recommends confirming negative results from a rapid antigen test with a PCR test. Antigen tests look for proteins on the virus’s surface and require thousands to tens of thousands of viral particles to be able to detect an infection. In cases where the sample has low amounts of virus, rapid antigen tests may be unable to detect a COVID infection and give a false-negative result. Multiple studies, including guidance by the CDC, concur that the sensitivity of rapid antigen tests are significantly lower than RT-qPCR. One study found that rapid antigen tests detected between 11.1% – 45.7% of RT-qPCR-positive samples from COVID-19 patients.
RT-qPCR can detect a miniscule amount of RNA, specific to the pathogen, and make exponential copies of it until there are over one billion copies of that particular RNA segment. This is why RT-qPCR is able to detect an infection at earlier stages, even when viral loads are low. RT-qPCR techniques are the most effective form of testing used in staff surveillance programs as they can detect minute amounts of viral particles, as low as 5.8 viral copies per microlitre of saliva.
Reduce Transmission With Frequent, Rapid Testing
A strategic testing plan accounts for the level of COVID risk within the groups tested, depending on the amount of interaction outside of the group and the potential for severe illness. In higher risk groups, such as the hospitality industry where individuals interact with the general public randomly, testing frequency should be increased to account for uncontrolled encounters. High risk groups can also include older adults or those with underlying medical conditions who are more likely to get fatally sick. In a lower risk group, such as learning pods where individuals tested have had limited exposure to others outside of the particular group, fewer tests will be needed to support ongoing activities.
Frequency of testing is critical for transmission reduction. Most universities that have surveillance testing programs are conducting baseline testing of twice per week, with adjustments for higher-risk groups. Compared to testing once a week, testing twice a week can increase the impact of a surveillance testing program in curbing viral spread from 55% to >90%.
Lengthier turnaround times could also have a significant impact on the ability to prevent an outbreak. Keeping the same testing frequency, a two-day rather than a same-day turnaround leads to a >30% decrease in ability to reduce the spread of the virus. A one-day turnaround vs same-day leads to a 15% decrease in ability to control viral spread.
Saliva Allows for Early Viral Detection
Ease-of-collection and minimising operational disruption are important when selecting the sample type for routine surveillance testing. Saliva is the ideal specimen as it can be reliably self-collected due to the straightforward and simple procedure, eliminating the need to hire and train on-site health personnel.
In addition, it is minimally invasive, increasing compliance among staff for repeated testing. Compared to nasopharyngeal swabs, saliva samples can detect pre-symptomatic infections earlier because they carry a larger viral load throughout the course of infection.
Decrease Costs and Increase Testing Efficiencies 5-Fold With Pooled Testing
Surveillance testing can be conducted in diverse group sizes as large as an entire manufacturing plant to smaller ones, such as an office team. Pooled testing allows for flexibility in the numbers of people tested which can reduce costs significantly and increase testing capacities. Individual diagnostic tests for SARS-CoV-2 can cost anywhere from £120 – £200, which is not a feasible or affordable solution for many businesses. Surveillance testing allows for pooling, and pooling even five individuals drops the average cost per test to £30 – £40.
How to Pool Strategically
The optimal pooling strategy minimises cost and disruption by identifying groups depending on the level of their interactions with one another. Pooling should follow the group format that already exists in current business operations so actionable results can be taken without affecting other teams in the case of a positive result. Examples of natural groups include work shifts, classroom cohorts, or hospital departments.
Pool size is also an important strategic consideration as pooling too many samples across an organisation can make it difficult to take action if a positive result is obtained, without significant impact on overall business operations. If pools are too small, testing and cost efficiencies are negligible.
In addition, as more people are pooled together, test sensitivity decreases due to specimen dilution. However, the loss in test sensitivity can be remedied with replicate testing where the same pool is run more than once to confirm results.
For example, if a manufacturing plant wanted to resume operations safely, they could first take a look at the natural groups that exist within their operations, such as those within particular shifts or work near one another. The next step would be thinking through the consequences of a positive pooled result and the implications. If the morning shift production line was pooled, and a positive result returned, the entire production line would be required to go home and self-isolate, impacting overall business operations. However, if the shift were split into two pools, and a positive result returned, only one group would be required to go home, while the other group could continue working.
Surveillance vs Diagnostic Testing: What’s the Difference?
When pooling samples, a positive result can be followed up with individual diagnostic testing to determine who the infected individual(s) is in the group. If a negative pooled test result is obtained, all individuals in the pool are presumed to be coronavirus-free at the time of testing.
This flexibility in settings where surveillance testing can be implemented means that it can be used as a tool across various industries. This is critical as diagnostic labs are overwhelmed by the influx of COVID tests requiring processing, leading to backlogs and days spent waiting for results.
While both surveillance and diagnostic testing detects the occurrence of infection, both have differing purposes.
What if Infection is Detected
If infection is detected within a group the following actions should be taken:
- Immediately self isolate all individuals from the identified group
- Refer the individuals for NHS diagnostic testing
- Decontaminate hotspots and surfaces within the building (surface PCR swab testing can be used to valid areas are clear)
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