Respiratory Virus Surveillance during COVID-19

ARI reports were summarized for the study population by week and age group from March 1, 2020, through June 30, 2021. Incidence rates (IR) of ARI reports and virus detections were calculated per 100 person‐years for the study period and for a pre‐pandemic period of similar length (March 1, 2016, to June 30, 2017); these rates were compared using incidence rate ratios (IRR) with 95% confidence intervals (CI). The detection of each respiratory virus as a proportion of reported ARIs was determined overall and compared by age group (<5, 6–11, 12–17, 18–49, ≥50 years). For analytic purposes, child is defined as age <18 years. An epidemic curve for the study period was generated by plotting ARI reports by RT‐PCR test result. Reported COVID‐19 cases in Michigan were obtained from the MI Safe Start Map (https://www.mistartmap.info/) and were used to indicate when COVID‐19 incidence exceeded 150 cases per million population per day. Dates when the “Stay Home, Stay Safe” order was implemented and when K‐12 schools were closed were also obtained from the MI Safe Start Map.
Frequencies of survey responses were calculated and compared for each survey period. Serology data were combined into three serosurveillance periods: summer 2020, fall 2020–winter 2021, and spring 2021. Seroprevalence of antibodies against SARS‐CoV‐2 N protein was determined overall and by age group. Statistical analysis was performed using SAS (v9.4, SAS Institute Inc., Cary, NC) and R statistical software (v4.1.0; R core team, 2021).