To Test or Not to Test: What Should an Employer Do? Thoughts from an Epidemiologist

Categories: Clinical Staff, For Employers, General, Recent Coverage

This blog was originally published on Business Insider

 

As many businesses face reopening, they are pondering ways to keep their workplaces safe. For many, the question of testing is top of mind. Should they offer testing? If yes, given all the concerns on test reliability, what kind of testing should they offer? Furthermore, who should be tested and how often?

In an ideal world, we would have rapid, highly reliable, relatively inexpensive tests available that would let us know who was currently infected. We would also, in theory, have accurate antibody testing, to tell us who was recently infected and potentially immune. Based on these types of tests, only those without current infection and/or evidence of previous infection/immunity would be allowed to return to work. This would decrease the likelihood of viral transmission in the workplace.

But even in that ideal scenario, we would still practice enhanced infection control by continuing to maintain at least six feet apart between workers, reducing the number of staff working at any given time, using masks or other protective equipment where close contact was impossible to avoid and more.

Symptomatic employees would be immediately excluded from entering the workplace, as would close contacts. Moreso, re-testing would occur periodically, at least for some initial length of time, to ensure that infection control measures are working.

Unfortunately, we are far from this ideal scenario. The main tests that are available as of this writing are the polymerase chain reaction (PCR) and antibody testing, both of which either have challenges with sensitivity (the ability to detect true positives) or specificity (the ability to detect true negatives). 

 

PCR tests and the danger of high false-negative rates

COVID-19 PCR tests directly test for the presence of the COVID-19 virus. This test is usually obtained by a nasal or throat swab, and just recently the FDA approved saliva testing. PCR testing indicates whether a patient is infected at the time of testing.

In theory, PCR testing of employees could help employers know who was currently infected. Infected employees would then isolate at home, according to the latest CDC guidelines, and those who were not infected could return to the workplace. In essence, the worksite would reopen virus-free. 

Sounds straightforward, right? Unfortunately, the nasal or throat swab PCR test can have a false-negative rate of up to 30%. That means for every 100 employees who are actually infected with the virus, 30 would be missed and could then spread the virus to others when let back into the worksite. 

 

So what should employers do if they choose to offer PCR testing?

  • Protect your high-risk employees. Knowing that you might miss up to 30% of people who are carrying the virus, it is especially important to keep high-risk people working from home, along with people who live with or care for high-risk individuals. Start by bringing back only low-risk employees who test negative for the virus. Another option might be to require 2 negative tests, 24+ hours apart, to reduce the chance of a false negative.
  • Re-test every 14-28 days. Unfortunately, testing cannot be one and done. PCR testing only tells you if you are infected at one point in time. So if you get infected a few days after you took the test, you may falsely assume you are still free and clear. And we are learning more and more that people can be asymptomatic with COVID-19, and still spread the virus. So the best thing to do is retest those employees who are coming to the office, every 1-2 incubation periods (14-28 days), to ensure that they are still negative. 
  • Budget accordingly. Cost may certainly become an issue as a result of re-testing. Some employers may consider testing a random sample of employees to reduce costs. 

 

Antibody (serology) testing cannot determine who is immune or not with certainty (yet)

Antibody tests measure the presence of virus-fighting antibodies that indicate immunity. These tests require a blood sample, either through a blood draw or in some cases a finger prick. Unlike PCR tests, which detect the presence of the virus itself, serology tests show whether an individual has ever had the virus. In theory, the presence of these antibodies indicates a person has a low likelihood of being infected again. 

However, we do not yet know the degree of immunity that people could have from these tests. Initial animal studies do suggest that protective antibodies are produced, but there isn’t much human data yet. There have been some reports that antibodies from the plasma of people who have recovered from COVID-19 can help severely ill COVID-19 patients. This suggests that human antibodies, at least initially, do effectively fight the novel coronavirus, but more rigorous studies are needed. 

In addition, we need to learn how long COVID-19-protective antibodies last. Antibodies to seasonal, common cold coronavirus have been found to decline steadily within a year of being infected, so some people can be reinfected a year later. But with the coronavirus that caused SARS in the early 2000’s, immunity was found to last for up to 3 years. We don’t yet know what pattern will emerge with this novel coronavirus.

Another issue is with the testing itself. There are accuracy concerns with some of the antibody tests currently on the market. One major worry is a potentially high rate of false positives, depending on the manufacturer. A false-positive result might wrongly give someone the impression that they have already had the virus and are producing antibodies to it (at least in the short term). 

 

What should employers do if they choose to offer antibody testing?

  • Vet the test carefully. Ask testing companies specifically for their false-positive rates and for information on any independent evaluations that have been conducted on their tests.
  • Protect your high-risk employees. Knowing that you might have some falsely positive employees, keep people at high risk for severe COVID-19 related illness working from home, along with those who share a home with high-risk individuals. Or consider doing PCR testing too, to see if anyone might have an active infection despite having a positive antibody test.
  • Re-test every 2-4 months. Even if the antibody test you choose is relatively accurate, we still don’t know how long these antibodies last. Studies of other coronaviruses suggest that antibody levels eventually wane. So the best thing to do is retest those employees who are coming to the office, every 2-4 months, to ensure that they are still producing antibodies. Again, costs are a consideration, which can be addressed by testing a random sample of the employee population. 

Newer tests have recently come online, such as rapid antigen tests (which detect fragments of viral proteins) and CRISPR tests (which latch onto RNA sequences from the virus). Not much information is available yet on how accurate these tests are and when they will be widely available. But as we have learned from the past few months, the situation is rapidly evolving. Employers should continue to monitor updates in this arena, in the event that these offer more viable testing options. 

Regardless of whatever combination of testing, or no testing, an employer chooses, it is important that they provide as safe an environment as they can for employees. Follow enhanced infection control practices as previously mentioned: maintain the six feet physical distancing, monitor employee symptoms, conduct regular temperature checks, etc. Planning ahead and being prepared to re-close if the number of symptomatic employees increases will be crucial. And continue following the CDC guidelines, as well as those from local and state health officials. 

 

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