ABSTRACT
Background. We characterize the evolution of symptoms in those with selfreported SARS-CoV-2 infections and the likelihood of seeking treatment or medical care during different waves of the pandemic. Methods. The NC-CCRP is a longitudinal observational study of 37,820 participants who completed a daily symptom log from April 2020 through February 2022, during which there were 5,167 self-reported COVID-19 infections. Three variant periods were defined as pre-delta, delta, and omicron, based on the predominant variant in North Carolina. Quasi-Poisson and logistic regression models adjusted for demographics and vaccination were used to assess COVID-19 symptoms and their duration and seeking treatment or hospitalization Results. Cough was the most reported symptom in all waves and increased from 77% pre-delta to 85% during omicron (p=0.001). Sore throat was more common during self-reported infections during omicron (71%), compared with 62% during delta and 54% pre-delta (p< 0.001). The largest change in proportion reporting a symptom was loss of taste or smell which decreased from 55% during pre-delta to 17% during omicron (p< 0.001). Compared with the pre-delta period, delta (incidence risk reduction, IRR 0.86;95% CI 0.79-0.93) and omicron (IRR 0.67;95% CI 0.61-0.73) were associated with lower symptom duration. Participants infected during the delta wave were more likely to seek treatment compared with either pre-delta (odds ratio, OR 1.32 95% CI 1.06-1.64) or omicron (OR 1.42;95% CI 1.21-1.67). Omicron period infections were associated with a lower likelihood of self-reported hospitalization compared with pre-delta (OR 0.26;95% CI 0.10-0.59) or delta (OR 0.26;95% CI 0.11-0.60). Vaccination was associated with a reduced likelihood of hospitalization (OR 0.35;95% CI 0.18-0.70). Proportion and Duration of Symptoms by Variant Wave;Unadjusted by Vaccination Status. Conclusion. Our study indicates evolution in symptom presentation and duration by variant period. The omicron wave was associated with shorter duration and lower severity of illness. Longitudinal tracking of symptomology and severity of a novel pathogen provide insights into the evolution of the pathogen in the community and is vital for public health and clinical response.
ABSTRACT
Background. Wearing a face mask is a primary public health method to reduce SARS-CoV-2 transmission. We assessed the association between self-reported mask use and risk of COVID-19 infection during three periods of the pandemic. Methods. We performed a nested case-control analysis within the NC-CCRP of adults >=18 years who completed daily syndromic surveillance surveys from April 2020 through February 2022, comparing self-reported cases to controls who never selfreported a positive test. We matched up to 10 controls to each case on calendar time of self-reported positive test and corresponding daily survey entry. Not wearing a mask was defined as responding "no" at least once in the ten days preceding the match date to "In the last 24 hours, have you worn a face mask or face covering every time you interacted with others (not in your household) within a distance of less than 6 feet?" Conditional logistic regression models of risk of COVID-19 infection were adjusted for demographics, vaccination status, and recent known exposure to COVID-19. We tested any days not wearing a mask during the Pre-Delta (July 1 2020-June 30, 2021), Delta (July 1- November 30, 2021), and Omicron (December 1, 2021 - February 28, 2022) periods. Results. Among 3,901 cases and 27,813 date-matched controls, there was a significant interaction between mask use and time period (p< 0.001). Prior to July 2021, the odds of a reported SARS-CoV-2 infection was 66% higher (aOR=1.66, 95% CI=1.43 - 1.91) among participants reporting at least one day not wearing a mask compared to those who reported no days (1592 cases, 11717 controls). During the Delta-predominant period, the results were similar (aOR=1.53, 95% CI=1.23 - 1.89;659 cases, 4649 controls). This association was attenuated during the Omicron-predominant period, where the odds of a reported SARS-CoV-2 infection was 16% higher (aOR=1.16, 95% CI=1.03 - 1.32;1563 cases, 10960 controls). Conclusion. While the effect of not wearing a mask remains significant, during the Omicron-predominant period we observed a decrease in the association between self-reported mask wearing and risk of SARS-CoV-2 infection. The increased transmissibility of Omicron, pandemic fatigue, and increasing population immunity are possible contributing factors.