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COVID-19 Asymptomatic Carriers and Antibody Tests

April 23, 2020
Published in: COVID-19, Infectious Disease

Older adult patient wearing a mask and getting her temperature checked

As experts work to slow the COVID-19 spread, they focus on issues such as learning how the virus spreads, determining who has the virus, and learning who has developed immunity. Because it's a new virus, but linked to other viruses, these answers are complex. Allison Baroco, MD, Infectious Disease Specialist at Augusta Health, and Stefanie Bartley, BSN RN an Infection Prevention Specialist, discuss two important concepts—asymptomatic carriers and antibody tests.

What is an asymptomatic carrier? How many asymptomatic COVID-19 carriers do we have?

"An asymptomatic carrier is someone who has contracted the virus, but who isn't showing any symptoms of the disease," says Bartley. "There have been instances where a person has tested positive for SARs-CoV-2 (COVID-19), but show no symptoms for the entire course of the disease."

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Disease stated on April 5 that the percentage of asymptomatic people with COVID-19 could be between 25% and 50% of those with the disease. Indeed, there are instances that indicate that could be true. In the CDC Case Study of the nursing facility in King County, Washington, 23 residents tested positive, and 13 were asymptomatic. Of the 600 sailors aboard the Theodore Roosevelt who had tested positive by April 16, about 60% had not shown symptoms. Aboard the Diamond Princess, 50% of those who tested positive had no symptoms at the time of testing, although 18% developed symptoms later.

"There is a bit of a continuum to this," adds. Dr. Baroco. "Some divide these patients into two categories: asymptomatic and pre-symptomatic. Pre-symptomatic patients may not report having symptoms at time of testing, but develop them later. Basically, though, at the time of testing, they are asymptomatic."

Why is this important?

"Whether you are asymptomatic or pre-symptomatic, you don't realize you are infected, but you can spread the disease to others," says Dr. Baroco.

Both explain that COVID-19 is spread by droplet. To spread the disease, infected droplets need to go from an infected person's mouth or nose into someone else's eyes, nose or mouth. That can happen directly, but not just through coughing or sneezing, but also through talking. Indirect contact through touching contaminated surfaces is also possible.

"By definition, asymptomatic means you have no symptoms, so to be responsible, we should all act as if we could be carriers of the virus," says Bartley. "Avoid close contact with others, and be sure to maintain that six foot social distance. Wear a cloth mask or face covering in public, to help contain your droplets and reduce the risk of spreading the virus to others. If you're not masked, be sure to cover your cough or sneeze. Wash your hands frequently and clean and disinfect high touch surfaces like counters and table tops thoroughly and often."

"I would also add to monitor yourself and be mindful if you feel as if you are developing any symptoms," adds Dr. Baroco. "Stay in tune to how you are feeling and stay home when you begin to feel unwell."

How do antibody tests relate to asymptomatic carriers?

"The theory is that if we develop a good test for antibodies, we will be able to define who is immune—and safe to go out and about—and who is not. It would help us determine who previously had infection, which we think may be protective of infection again in the near future. We do not know the long term significance though. Many see this as the key for our lives returning to 'normal'. This is exciting technology that is rolling along quickly, but it's too early to tell how we will be able to use this technology," adds Dr. Baroco. "There are just a lot of unknowns."

Those unknowns include cross-reactivity. This means that the test might confuse other coronavirus antibodies with those specifically for COVID-19. For example, coronavirus variants also cause the common cold. Cross-reactivity means that you may show antibodies for COVID-19, but never had it—although you had a cold six months previously.

Another unknown is that the immunity provided by COVID-19 is not fully understood. Does one infection provide life-long immunity? Or does the virus vary when it reproduces, like flu virus does, so you might have it more than once? Also, an adequate immune response usually takes up to four to six weeks after someone has been exposed to the infection.

"So while there is a lot of hope for an antibody test, and everyone would like to be able to tell who has had the virus and who is immune, there are too many uncertainties to know what role the antibody testing will serve and when the testing will be accessible," says Dr. Baroco.