A new study in JAMA Network Open involved giving wearable sensors to adults during the 2018-19 flu season to monitor physical activity levels and found that participants with influenza-like illness (ILI) symptoms were significantly less active than their healthy peers.

The authors suggest these findings can help quantify the invisible public health burden of viral illnesses that go undocumented and unreported.

Only 19% sought medical care

The authors of the study used daily steps taken as a proxy for activity levels. A total of 15,122 adult volunteers with a median age of 32 wore commercial sensors between Oct 1, 2018, and Jun 30, 2019, as part of their involvement with the Achievement application from Evidation Health, Inc., which tracks healthy habits, including minute-level steps.

The participants were mostly White (86.9%) and female (86.7%), and almost all (99.3%) had at least a high school diploma.

Every 2 weeks, the authors of the study had participants fill out a survey asking them to report any ILI in the previous 14 days. If participants reported symptoms, they were prompted to share specific details of symptoms, date of symptom onset, recovery date, healthcare-seeking behavior, diagnosis of ILI, lost workdays, household illness, and vaccination history days.

For all ILI events reported, 18.8% participants sought medical attention, and 61 (0.4%) were hospitalized.

From the first day of ILI symptoms through day 10, steps differences were notable and significant between sick and healthy participants, with a mean of 924 steps lost on the worst day of an ILI event. Over the course of the ILI (days 0 to 10), the mean cumulative loss was 4,437 steps, while steps did not change significantly during control periods.

Using weighted modeling to approximate the US population, the authors concluded that a total of 255.2 billion steps were lost during ILI events in the United States during the study period.

"This finding reflects significant changes in routines, mobility, and employment and is equivalent to 15% of the active US population becoming completely immobilized for 1 day," they wrote.

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