Coronavirus

Facing overloads, CDC restricts Covid-19 tests to those with symptoms

"We need to be much more creative about using the available technology that we have."

Faced with a pressing "testing crisis," the Centers for Disease Control and Prevention has adjusted its Covid-19 testing guidelines, taking a more restrictive approach.

As of August 24, the CDC advised people they do not need to be tested unless they are showing symptoms, are in a vulnerable subgroup or receive other guidance from their city and state public health authorities.

While the CDC's update may lessen stress on overwhelmed labs and manufacturers, it may also result in a spike in Covid-19 "silent spreaders." These are asymptomatic carriers of the virus — people who feel fine and can unwittingly transmit the novel coronavirus to others.

"This is a tough call," Matthew Ferrari, an epidemiologist at Penn State, tells Inverse. "The idea is that we would have sufficient testing resources for everyone to be tested whenever they want to. But given that our system is currently strained under a severe testing burden, with long lags in return time, I can at least appreciate a recommendation to prioritize testing to those most at risk."

What part of the Covid-19 pandemic do you think causes the most confusion? We want to know. Take the Inverse reader survey.

Testing in the United States — Depending on where you live, getting a Covid-19 test can be an efficient, speedy endeavor or a frustrating, delayed process. In some places, like Arizona and California, people report waiting days for a testing appointment, standing in line for hours at testing locations, or waiting a week or more for results. In New Mexico and New York, testing appears to be widely accessible and relatively quick.

However, due to manufacturing issues, processing lags, and supply shortages, the United States as a whole is struggling to scale up mass testing to identify and isolate those infected — a critical strategy in getting the pandemic under control. Because of supply chain bottlenecks, many labs aren't running "anywhere near capacity," Reuters reports.

Currently, U.S. labs run about 700,000 diagnostic tests daily, a fraction of the estimated five to 20 million tests needed per day for people to safely return to work in the United States.

Meanwhile, even where there are enough tests available, some people are using a negative test result to justify shirking public health precautions like wearing a mask, social distancing, and hand hygiene. But no test is an "antidote," Lindsay Keegan, an epidemiologist at the University of Utah, tells Inverse.

What's new from the CDC — Per the CDC's guideline change, a person does not necessarily need to be tested, even if they've been in close quarters with someone infected with Covid-19 or attended a public gathering in an area with spiking Covid-19 case counts.

According to the agency, "diagnostic testing categories have been edited to focus on testing considerations and actions to be taken by individuals undergoing testing."

But this calls into question how to prevent asymptomatic patients from spreading the disease. Between 20 to 40 percent of infected people never show symptoms, some studies suggest. Importantly, researchers still don't know if this group transmits the virus as efficiently as those showing symptoms.

The updated guidance may be confusing for the public who's heard resounding calls from public health experts to test as widely and as often as health resources allow.

The CDC's testing guidance updated August 24.

The issue with asymptomatic testing — Along with a possible Covid-19 treatment or vaccine, widespread contact tracing, and public health precautions, testing is key to curbing the virus' spread. Take other countries like Taiwan, South Korea, and Singapore, who were able to test millions of individuals rapidly and effectively, symptoms or not, and in turn, dramatically curbed viral transmission.

"The reason we need to test everybody is so that we can figure out who is infected and isolate them," Keegan explains. The goal is to stop secondary infections before they can root.

"The earlier you can put someone in isolation, the better," she says. "That [process] could be symptom-based or that could be test-based. It's much easier to get people to comply with isolation if they are testing positive."

However, a major concern with widely testing asymptomatic people, Keegan stresses, is that people may be tested too early after exposure. In turn, health providers might miss their window of infection, and a negative result could lend people a false sense of security. Since it typically takes five days for symptoms to appear (this window ranges from two to 14 days), when you get your test and how long it takes to receive results is crucial.

"Treating testing like it's some sort of treatment or some sort of an alternative to careful behavior changes is problematic," Keegan says. "I believe that that's what the CDC is concerned about and that's why they are shifting away from the policy of testing asymptomatics. It changes people's behavior to do potentially more risky things versus, if you were exposed, you should treat yourself as if you got infected for 14 days — that's a lot safer."

It's better if everybody who has had an exposure event treats themselves as if they're infected for two weeks, rather than get tested without symptoms, Keegan advises.

Who should get tested for coronavirus?

Keegan adds the caveat that there are high-density places, like long term care facilities or dorms, where everyone should be tested.

Meanwhile, Ferrari is concerned that the latest guidance will lead to confusion as many organizations, particularly universities, are implementing surveillance testing programs.

"Surveillance programs are going to be critical to our ability to trigger targeted actions rather than the county- or state-wide closures that have negative consequences for so many," Ferrari says.

"Given an exposure, we really want to test folks before they are symptomatic to maximize the chances that we can prevent them from transmitting to others... "

But currently, although the guidance specifically mentions surveillance programs, it is "not very clear about their important role in monitoring overall prevalence and trends, and the importance of individuals complying with these programs," he adds.

Ultimately, Ferrari thinks people should be tested before they show symptoms. The issue is that, in some places, there are simply not enough tests.

"Given an exposure, we really want to test folks before they are symptomatic to maximize the chances that we can prevent them from transmitting to others and to limit the additional burden on contact tracing," he says. "If someone has a reasonable suspicion of exposure and the capacity to do so, they should seek a test and self-quarantine until they have a test result or 10 days have passed."

If someone is in a place where testing delays are so long, they're unlikely to get the results back quickly, Ferrari says people should still self-quarantine.

That's where rapid diagnostic tests are valuable, Ferrari says.

A nurse practitioner administers COVID-19 tests in the parking lot at Brockton High School in Brockton, MA under a tent during the coronavirus pandemic on Aug. 13, 2020.Boston Globe / Contributor

Moving forward, with creativity— Ferrari says rather than unilaterally exclude all people without symptoms, there is another way we can relieve the testing crisis: rapid diagnostic tests (RDTs).

"These are tests that may have low sensitivity, but can be done quickly, easily, and cheaply without burdening the lab-based diagnostic system," Ferrari says. "Rapid tests, that sacrifice sensitivity for speed and cost, may return high rates of false negatives, but if individuals are tested frequently, it is unlikely that an RDT would be negative multiple times for an individual who was truly infectious."

At this stage in the pandemic, rather than hand wringing over tests with low sensitivity or specificity, Ferrari says, "we need to be much more creative about using the available technology that we have." He reasons that low sensitivity tests can be very useful in identifying clusters of infections. From there, researchers can apply their "gold-standard diagnostics."

"Rapid results mean that every other part of the process can work more smoothly — isolation will be more effective, contact tracing is more likely to find newly exposed cases before they become transmissible," Ferrari says.

As people navigate the confusing landscape of Covid-19 mixed messages, federal health guidelines from the CDC and from your city and state health departments can act as guideposts. Regardless of where these public health authorities come out on who, where, and how much to test, that decision really shouldn't change behavior when it comes to social distancing, wearing a mask, and washing your hands.

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