October 06, 2020

Who benefits from sentinel testing? You and everyone you know

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rep sentinel testing swab CREDIT 550pxSentinel testing at UAB uses a self-administered swab to identify COVID-19 in asymptomatic employees and students, bringing the invisible spread of the disease into view. The test takes five minutes or fewer and results are returned within 36 hours.COVID-19 thrives in the shadows. One of the reasons why the current pandemic is so much more widespread than the SARS outbreak in the early 2000s is the problem of "silent spread" — cases where the sources did not know they were spreading SARS-CoV-2, the virus that causes COVID-19, because they had no symptoms at the time.

A systematic review of the available evidence published in the journal Annals of Internal Medicine in June 2020 found that 40% to 45% of confirmed COVID-19 infections were in asymptomatic people. The authors also noted that asymptomatic people "can transmit the virus to others for an extended period, perhaps longer than 14 days." So even if everyone who feels ill stays home and isolates themselves as recommended, COVID-19 could continue to pass from person to person. At a recent virtual town hall meeting on campus, UAB infectious diseases expert Michael Saag, M.D., compared SARS-CoV-2 to a ghost. “The virus is lurking,” he said. “We know it is there, but we can’t see it.”

Making the invisible, visible

How many people have COVID-19 but don't know it? How many are going about their normal routines — going to work or school, interacting with friends and family and co-workers — while they shed live virus? These questions are particularly urgent at institutions such as UAB, with tens of thousands of students and employees on campus.


A positive test may not sound like good news, but it can be. That result is an early warning sign — and it could potentially save the lives of family, friends and co-workers who would otherwise have been exposed. You can compare it to dumping water on a smoldering fire.


Sentinel testing brings this invisible, asymptomatic spread into view. Each week, a randomly selected subset of UAB employees working full-time on campus, or coming to campus regularly in a hybrid status, receive an email offering them the opportunity to take part in voluntary sentinel testing. (Students are selected for sentinel testing daily, and testing is required for some students, but otherwise the procedure is the same.) Employees select a date and time during that week to go to one of six locations on campus and in the community for COVID-19 testing. All participants are asymptomatic; anyone who reports symptoms through the daily UAB Healthcheck will be evaluated separately by Employee Health. Anyone who has had a positive COVID-19 test in the past eight weeks is asked not to participate.

The testing itself takes five minutes or fewer. A worker hands the employee a swab, which the employee inserts about one inch into each of their nostrils to collect a sample. The sample is taken to a research lab on campus for highly accurate PCR testing, and results are returned within 36 hours. Employees with negative tests receive an email; employees who test positive receive a call from Employee Health with detailed instructions on how to care for themselves and those around them.

The benefits of a positive test

By testing just 2.5% of those on campus each week, experts at the School of Public Health have calculated, UAB can get an accurate estimate of the prevalence of asymptomatic COVID-19 carriers campuswide. "The primary goal of sentinel testing is to have a pulse on asymptomatic spread of the virus in the community and to ensure that any new infections are detected promptly," said Anupam Agarwal, M.D., executive vice dean of the School of Medicine.

rep sentinel testing rack CREDIT 550pxBy testing just 2.5% of those on campus each week, experts at the School of Public Health have calculated, UAB can get an accurate estimate of the prevalence of asymptomatic COVID-19 carriers campuswide.A positive test may not sound like good news, but it can be. That result is an early warning sign for the employee — and it could potentially save the lives of family, friends and co-workers who would otherwise have been exposed to that employee. You can compare it to dumping water on a smoldering fire. Contact tracers with Employee Health reach out to anyone that the employee has been in close contact with — closer than six feet for 15 minutes or more over a 24-hour period. Isolation for the positive employee, and their close contacts, can stop a potential outbreak before it goes any farther.

The positivity rate on sentinel testing is closely tracked by UAB experts in Employee and Student Health, and by the university's Incident Command Committee (see membership here and learn more about the committee’s mission in this UAB Reporter article).

"We review results of sentinel testing every week," said Agarwal, who is one of the Incident Command Committee’s 20 members. "Fortunately, the sentinel testing results so far are showing no signs of alarm for our employees.” Sentinel testing at UAB began in July; consistently, 1% or less of those tested each week have had COVID-19. “However, we will closely monitor and continue our sentinel-testing efforts," he said.

“We really need everyone to take part if they are offered sentinel testing. By declining to take part, UAB community members are not giving themselves, their co-workers and their loved ones the opportunity to benefit.”

Any increase in the positivity rate over time “alerts us to see if those positive cases are coming from any particular floor, building or other location,” Agarwal said. If a number of employees from a specific building test positive over a few weeks, for example, leaders can investigate the environment to determine if a shared break area or piece of equipment could be involved, or if education on social distancing and hygiene precautions is necessary.

‘You aren’t taking a test away from anyone’

"Just like universal face coverings and social distancing, sentinel testing is a critical element of UAB’s health and safety plan," said UAB Chief Risk and Compliance Officer Katie Crenshaw, J.D., who chairs the Incident Command Committee. "Sentinel testing indicates to our medical and public health experts if the virus is starting to pop up more in asymptomatic people.”

Crenshaw has seen survey results from employees who decline to participate in sentinel testing because "they don't have any symptoms and they don't want to take a test away from someone who does," she said. But this is not the case. Sentinel testing is a dedicated resource that does not take testing away from others who may feel sick or are experiencing symptoms.

“You aren’t taking a test away from anyone,” Crenshaw said. “We really need everyone to take part if they are offered sentinel testing. By declining to take part, UAB community members are not giving themselves, their co-workers and their loved ones the opportunity to benefit.”