Flu-like illnesses appeared to spread through primary care office visits

A new study's findings on the spread of influenza offered lessons on reopenings of outpatient clinics during the pandemic and the value of virtual visits for patients with suspected respiratory infections, the authors said.

Patients exposed to influenza-like illness in the medical office setting were more likely to return with a similar illness within two weeks compared with nonexposed patients seen earlier in the day, a study found.

Researchers reviewed billing and scheduling data from a health care information technology company for visits occurring in 2016 and 2017 at 6,709 office-based U.S. primary care practices with more than 100 million care encounters. They used scheduled start times of visits to classify appointments as unexposed or exposed to a patient with flu-like illness. Visits were considered unexposed if they were scheduled to start at least 90 minutes before the first flu-like illness visit of the day occurred at that practice. Researchers did a falsification test using diagnoses of urinary tract infections or back pain. Results were published online on Aug. 1 by Health Affairs.

Among 105,462,600 visits, 10,737,587 (10.2%) occurred on the same date as a flu-like illness visit at the same practice. Among these visits, 3,394,777 (31.6%) occurred before a patient with flu-like illness, whereas 7,342,810 (68.4%) occurred after. In the study, 2.7 patients per 1,000 returned within two weeks with flu-like illness. Patients were more likely to return if their visit occurred after a flu-like illness visit versus before (adjusted difference, 0.7 per 1,000 patients; 95% CI, 0.6 to 0.8). The change represented a 31.8% increase, the study authors calculated.

They noted that with more than 7.3 million visits taking place after a flu-like illness visit in the study, the adjusted difference could result in 5,140 excess flu-like illness visits potentially attributable to appointment timing.

Limitations include that the database didn't track patients who sought care at an urgent care or emergency setting, suggesting the findings likely undercount true in-office flu-like illness transmission. Also, they could not determine exposure in the waiting room versus an exam room.

“[A]lthough our study provides insight into the risk posed by patients with influenza-like illness in the outpatient setting, this might not generalize to the current COVID-19 pandemic, which is the most urgent policy priority,” researchers wrote. “However, it is plausible that the same principles that drove the results of this study could apply for COVID-19 as well. In addition, maintaining patient safety during influenza season remains a perennial concern.”