Think you’ve recovered fully from COVID? Your Fitbit may say otherwise

If you’ve had COVID-19 and are wondering why, months later, you don’t feel like your old self, the answer might be wrapped around your wrist, according to a study published Wednesday by Scripps Research.

Scripps scientists sifted through wearable device data to understand how coronavirus infections affect heart rate, sleep and activity levels. They found that it typically takes two to three months for these measures to return to pre-COVID levels. But in some people, those changes drag on for far longer with researchers only just beginning to understand why.

The findings, published in the scientific journal JAMA Network Open, show that the road to recovery is longer and harder for COVID-19 than for other respiratory infections. Researchers say monitoring wearable gadgets for telltale signs someone is sick has a variety of uses, from encouraging people to get tested and seek medical care to helping officials spot emerging outbreaks.

Jonathan Wosen on San Diego News Fix:

“No one’s really done this before,” said Jennifer Radin, an epidemiologist at Scripps Research and leader of the study. “It definitely, objectively gives evidence that what people are experiencing can be measured with these devices.”

It’s just the latest example of researchers mining this ever-growing treasure trove of data. One in five Americans owns a wearable device, such as a Fitbit or Apple Watch. These gadgets monitor how fast your heart’s thumping, your feet are running, and how often you toss and turn at night.

“If you’re able to really characterize what’s normal for each person, then you can identify these more subtle changes that may indicate they’re coming down with a viral illness,” Radin said.

She cites heart rate as an example. The American Heart Association says a healthy adult’s resting heart rate can vary from 60 to 100 beats per minute, but no one person’s pulse varies that drastically. A smaller jump from, say, 60 to 75, could be an early indicator something is amiss.

Detecting such subtle signs is the goal of Scripps’s ongoing DETECT study (Digital Engagement & Tracking for Early Control & Treatment). Participants share their data by downloading the MyDataHelps app on the App Store or Google Play. Names and other personal identifying information are removed before researchers look at the data.

Between March 2020 and January, more than 37,000 people enrolled in the study. Of those, 875 participants who had respiratory infections were tested for COVID-19, with 234 testing positive.

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Radin’s team found that those with COVID-19 tended to sleep longer and were less active than study participants with other respiratory infections. Their heart rates differed, too, dipping below pre-infection levels about a week after symptoms started and then shooting up.

The heart rate pattern was a surprise, Radin says, and suggests that the coronavirus is affecting the part of the nervous system that controls pulse and other bodily functions we don’t think about consciously.

“It’s still a hypothesis,” she said. “We don’t know exactly why this is occurring, and that’s something we hope to better understand.”

It took about two to three months for most people’s data to return to pre-infection levels. But in about 14 percent of cases, heart rates stayed higher than normal for more than four months. Researchers found that these volunteers tended to have had worse symptoms during the initial phase of the disease, such as body aches and trouble breathing.

That may mean that a bad initial bout of disease increases your risk of long COVID, a poorly understood condition that can leave some people with chest pain, shortness of breath and trouble thinking clearly for months.

Going forward, the research team plans to use wearable device data to understand how people respond to coronavirus vaccines. And researchers are also planning a study in San Diego to see whether wearable device data can predict changes in the number of COVID- and influenza-like infections reported by county officials. They hope to enroll 7,000 to 10,000 participants and to show that their data can predict outbreaks and whether current public health strategies are working.

The DETECT study is ongoing. To learn more, visit detectstudy.org.