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Fitbits ‘can tell 92% of people with Covid they are infected up to SEVEN days before symptoms’

FITBITS can help detect if people have Covid, sometimes before their symptoms have shown, a study shows.

The common wearable devices track patterns in heart rate, which can be used to look for abnormalities caused by viruses.

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Fitbits can help detect if people have Covid, a study has shown[/caption]

People who are infected with the coronavirus typically do not show obvious signs – such as a cough, high temperature or loss of taste and smell – for five or six days. 

But their body vitals may change in this “presymptomatic” period.

These invisible changes could be used as indicators of the very early stages of infection. 

Finding Covid cases before their symptoms show would be hugely beneficial for stopping the spread of the virus.

People are still infectious during the presymptomatic period and unknowingly spread the virus onto others. 

More than half of transmission of the virus is caused by people who are either presymptomatic or asymptomatic – meaning they never show symptoms at all.


Researchers at Stanford University, California, collected data on 106 people who wear Fitbits.

Twenty-five of them had been diagnosed with Covid-19 between February and June, 11 had another illness, and 70 were healthy.  

Their Fitbits had collected information for months on the heart rate, activity and sleep.

For each person, the researchers worked out their baseline resting heart rate, which varies from person to person. 

An altered resting heart rate is known to be a sign the body’s immune system is ramping up in response to a pathogen.

Dr Gareesh Bogu and his team put this data into a system which was then able to flag periods of time where each person’s heart rate was abnormal – either too high or too low.

The algorithm was able to detect heart rate abnormalities in 14 (56 per cent) of the 25 Covid patients in the days before their symptoms started.

Gireesh K. Bogu, PhD
This graph shows when an individuals resting heart rate was normal, and then abnormal in the period of their Covid infection[/caption]

Their heart rates started to change seven prior to signs of the disease, which may mean the virus starts to alter the body’s vitals as soon as a person is infected. 

The system also found abnormalities in nine (36 per cent) of infected people roughly two days after their symptomatic period. 

Only two of the people with Covid did not show any changes in their heat rate.

When do Covid symptoms start?

On average it takes five to six days from when someone is infected with the virus for symptoms to show, according to the World Health Organization.

However it can take up to 14 days, which is why you must self-isolate for two weeks if you have been in contact with someone with the disease.

During the “presymptomatic” period of the disease, when someone is not showing symptoms, they are still infectious.

One piece of research found people are most contagious one day before their symptoms begin.

And scientists have said people with Covid-19 ‘shed’ or excrete the virus at ‘high levels’ during the first week of symptoms.

People with the coronavirus had around 89 hours of abnormal resting heart rate during their infectious period compared to 25 hours in a healthy person.

However, the tool was not precise enough to distinguish Covid compared to other viruses.

Of the 11 participants with non-Covid illnesses, seven had abnormal heart rates comprising around 87.5 hours each.


The study, published as a pre-print paper, shows promise for using fitness tracker devices to warn people they may be infected.

Dr Bogu and colleagues wrote: “Our work suggests that wearable sensor data could be used as a marker for early prediction of COVID-19.

“SARS-CoV-2 is contagious multiple days before symptom onset and diagnosis, thus enhancing its transmission through the population.”

More work needs to be done before this could be used in the real world, however. 

Because there is no blanket “normal” resting heart rate, and it varies widely between individuals, it’s not possible to make a generic algorithm.

But the scientists say the technology “has the potential to alert individuals of illness prior to symptom onset and may greatly reduce the viral spread”. 

If a method can be honed down, the team said it would “reduce transmission and end the pandemic”. 

The team said using data from devices such as the Apple watch or Garmin watch could also help with Covid detection.

It’s not the first time researchers have come to the conclusion that wearable technology could play a role in diagnosing Covid-19 after a stream of studies started as early as spring last year.

An earlier study from Stanford University found changes in heart rate, number of steps taken and sleep were evident in 80 per cent of 31 people with Covid who wore Fitbits. 

In some cases, signs of infection were clear nine days before the tell-tale symptoms of a cough, fever or loss of taste and smell started.

Previously US researchers found the Oura – a ring which tracks activity and vitals – can detect coronavirus three days before symptoms with 90 per cent accuracy. 

King’s College London launched a study in the summer after inviting smartwatch owners to join.

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