OBJECTIVES : To estimate the prevalence of diagnosed/undiagnosed/misdiagnosed COVID-19 (COVID) vs. seasonal influenza (flu) in the US during the 2019-2020 influenza season.

METHODS : Prevalence of COVID/flu was determined from a nationally representative e-survey of a random adult sample. Additionally, demography, comorbidity, concomitant medications, and health-resource utilization (HRU) were evaluated. Undiagnosed (i.e., symptomatic/no diagnostic testing) or misdiagnosed (i.e., symptomatic/testing negative) COVID/flu was identified from responses to COVID-specific 8-symptom checklist (CSC) derived from a 25-symptom questionnaire. Based on testing or CSC status, respondents were grouped into “neither”, “dual diagnosis”, “COVID-only” and “flu-only” cohorts. Diagnosed COVID or flu was estimated from the positive tests. Overall COVID or flu rates were estimated as a sum of diagnosed, undiagnosed, or misdiagnosed for each.

RESULTS : Of the 1,123 respondents (mean age=39.1 years), 21.5% (242/1123) reported COVID/flu symptoms. Amongst respondents who underwent testing (143/1123), 22.4% (32/143) tested positive for COVID and flu (dual-diagnosis) concurrently, 7.0% (10/143) for COVID-only and 30.8% (44/143) for flu-only. Overall, 40.9% respondents had undiagnosed COVID/flu (99/242); 8.7% (21/242) and 32.2% (78/242) had undiagnosed COVID-only and flu-only, respectively. Of 39.8% misdiagnosed respondents (57/143), 23.0% (33/143) and 16.8% (24/143) had misdiagnosed COVID-only and flu-only, respectively. Overall, COVID and flu rates were 8.5% (96/1123) and 15.9% (178/1123), respectively. Seventy-five percent diagnosed with COVID (32/42) were also flu-positive (dual-diagnosis). Sensitivity of CSC was 97.6% (41/42 that tested COVID-positive would identify as COVID with only CSC). Compared to neither cohort (n=881), the dual-diagnosis cohort (n=32) had significantly higher comorbidities and concomitant medications followed by COVID-only (n=64) and flu-only (n=146) cohorts. Dual-diagnosis cohort had higher HRU; with greater hospital-stays, ICU-stays, and ventilator-use, as well as longer hospital and ICU length-of-stays.

CONCLUSIONS : These study findings demonstrate that the prevalence of COVID was half the rates of flu and 75% COVID-positive respondents were also flu-positive (dual-diagnosis). Dual-diagnosis cohort had highest HRU and comorbidity rates.