One 28-year-old woman developed a fever, dry cough, and shortness of breath during a trip to New York City in February, but her doctor assumed it was the flu. Was it actually COVID-19, and what would the implications be?

Toward the end of February, I traveled to New York City for a work trip. On day four or five, I started to feel ill. I did not have a thermometer, and so I did not think to take my temperature. But I was extremely tired, had a mild sore throat, developed a dry cough, and had trouble walking around the city due to shortness of breath.

Back home in Ann Arbor, Michigan, a week later, I was waking up in the middle of the night with coughing fits. The cough was “unproductive,” a term that I have now learned means I was not able to expel mucus. The coughing spells would be overwhelming, often leaving me hoarse and feeling like I was going to throw up. My shortness of breath was growing more persistent, as well. Generally active and an avid walker, I could barely take my dog outside for a few minutes a day before needing to sit down.

Finally after about two weeks, I went to see a doctor. “This just doesn’t feel like anything I’ve ever had,” I remember telling him. He listened to my lungs, which sounded more or less okay. He declared it “a virus,” insisting it might take two or three weeks to fully run its course. Coronavirus crossed my mind because of the shortness of breath, but very few people were talking about it at the time and it was only being reported on the West Coast. I thought to myself, If it was even possible, he’d test me, right? I did not realize how little testing was actually being done anywhere in the country at that time.

About one week after I got home from my trip on March 1, New York City’s first official diagnosis of COVID-19 was announced. Now that weeks have passed, I am recovered from that peculiar respiratory illness. And as I learned about the novel coronavirus, I have become more curious as to whether I may have contracted it in February.

Perhaps a lot of us are thinking about our most recent illnesses, and wondering the same thing as I am: was it a bad cold, the flu, or perhaps COVID-19? So I reached out to doctors who might be able to help me figure it out—and explain what it would mean if I did have the coronavirus.

Why anyone who was sick earlier this year might have had undiagnosed COVID-19

Scientists believe the virus emerged in China in December 2019. International travel continued throughout January, as cases popped up in other destinations—such as Australia, Bangkok, South Korea, France, the UK, Japan, and Russia. The US confirmed its first COVID-19 case on January 21. But the virus was already spreading other places, too.

By the time we recognized the start of the pandemic in the US, it’s very possible it was already here and well-established. Part of the problem in tracking the virus has been its vague symptom profile, which is relatively similar to symptoms you would have with the common cold or influenza, especially in the virus’s milder forms: dry cough, pressure of pain in the chest, shortness of breath, nausea, and diarrhea.

Pandemics start slow, but pick up heat as community spread begins. According to Greg Schrank, MD, MPH, an associate hospital epidemiologist at the University of Maryland Medical Center and COVID-19 response co-incident commander, epidemiological studies and genetic analysis of the virus indicate COVID-19 was likely “circulating in these epicenter communities for weeks to months” before those locations began to experience a surge of cases.

It’s not out of the realm of possibility that this virus has been spreading in the United States since the very early part of the year, perhaps in early January or very late December, Jagdish Khubchandani, PhD, MPH, an associate chair and professor of health science at Ball State University in Indiana, tells Health. “Given the timelines and incubation period reported by studies, it could be possible that many Americans had this infection way back and we are just now getting to see the severe most cases,” he says.

When the virus is just beginning to spread in a community, with low numbers of infected people, “the time it takes for the number of cases to double” was observed to be a week or more, Dr. Schrank tells Health. “The doubling time is primarily determined by the incubation period along with the number of people that are actively infected and can spread the virus to others,” he says. “As the prevalence of infection increases in a community, this doubling time decreases, and the growth of the epidemic becomes exponential.”

Early on, the virus was likely making the rounds, but in relative stealth mode, misperceived as other common respiratory illnesses. Now that we have a critical mass of patients and improved testing access, we are starting to experience rapid doubling of the virus, which leads to exponential growth and a surge of infections. One problem of not testing early and widely is that we don’t currently know who’s been infected—which could provide important insight for individuals and the country at large.

The implications of knowing if you've been exposed

If you contract COVID-19 and then subsequently fight the virus off, the theory among many scientists is that you become immune to reinfection. Like similar coronaviruses, antibodies develop to help your body defeat the illness, and the body develops at least short-term immunity as those antibodies linger around after COVID-19 is gone.

This is why knowing who has immunity could be critical as we await a vaccine. “Many people will become infected,” William Schaffner, MD, a professor of medicine in the division of infectious diseases at the Vanderbilt University School of Medicine in Tennessee, tells Health. “The question is, will we be able to determine who has been infected and who remains susceptible? We would have to test everyone to see if they have evidence in their bloodstream of proteins that would indicate they’ve been exposed.”

To look for those proteins, we need a screening method. “Laboratories are working to develop a blood test to look for antibodies which are a sign that a person was recently infected with COVID-19,” says Dr. Schrank. As of April 2, the FDA issued its first approval to Cellex, Inc. for a test that would allow medical professionals to look for antibodies. About 30 other companies have tests like this in the works, as well.

Of course, knowing if you were exposed and asymptomatic, or had a mild form of COVID-19 and now in the clear, would relieve a lot of stress and wonder. But nationally, knowing who’s immune could have broader implications. “It might, if it were quick and easy, determine who needs to be vaccinated and who doesn’t,” says Dr. Schaffner. He also says it could “help communities decide how open they could be again.”

Germany has been working on widely testing for immunity, so they can get certain people back to work sooner rather than later. Some leaders in the UK are also pushing for “immunity passports,” which would clear some essential workers to get back to their jobs by testing to see if they’ve been exposed to the virus.

Knowing who has already been affected is helpful because antibodies can also be used to treat COVID-19. “The FDA just approved use of antibodies from recovered patients for new cases as an emergency investigational new drug protocol,” says Khubchandani. On March 28, Houston Methodist in Texas became the first hospital in the country to offer a plasma transfusion for COVID-19; Mount Sinai Medical Center in New York City also began offering them. The hope is that lending plasma with antibodies that developed in response to the novel coronavirus will help some patients overcome the disease easier.

What to do now

Dr. Schaffner senses that a lot of people will want to know if they’re immune. “We’d like to test first responders; many people of a certain age will want to know,” he says. Dr. Schaffner adds that it’s about making a test streamlined, so it can be made widely available.

If there’s a silver lining to this global pandemic, it’s that every ounce of the world’s scientific innovation is being thrown at the coronavirus right now. “We must remain optimistic, as all textbook and novel methods are being tried [to fight COVID-19],” says Khubchandani.

In the meantime, even if you think you may have been infected, it’s important to act like you’re supremely vulnerable—for your sake, and for others’ sakes—because there’s no way to know for sure. “Social distancing is absolutely key,” says Dr. Schaffner. “It is the thing we can do today to prevent acquisition of infection, because it’s transmitted within close contact. Mild symptoms or no symptoms, you can be contagious; anyone can just breathe out the virus, and if you are standing close, and could get infected. That is why everyone has to maintain social distance, you can’t just focus on who has cold or fever.”

Personally, I’m hoping for that antibody test, so I can figure out my own level of immunity. But if I never get it and never learn if my illness earlier this year wasn't COVID-19, I’m more than okay practicing social distancing—to make myself and my community safer during this life-altering pandemic.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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