Rate and severity of suspected SARS-Cov-2 reinfection in a cohort of PCR-positive COVID-19 patients.

Objectives: To estimate the burden and severity of suspected reinfection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Methods: A retrospective cohort of members of Kaiser Permanente Southern California with PCR-positive SARS-CoV-2 infection between 1st March 2020 and 31st October 2020 was followed through electronic health records for subsequent positive SARS-CoV-2 tests (suspected reinfection) ≥90 days after initial infection, through 31st January 2021. Incidence of suspected reinfection was estimated using the Kaplan-Meier method. Cox proportional hazards models estimated the association of suspected reinfection with demographic and clinical characteristics, hospitalization, and date of initial infection.

Results: The cohort of 75 149 was predominantly Hispanic (49 648/75 149, 66.1%) and included slightly more females than males (39 736, 52.9%), with few immunocompromised patients (953, 1.3%); 315 suspected reinfections were identified, with a cumulative incidence at 270 days of 0.8% (95% confidence interval (CI) 0.7-1.0%). Hospitalization was more common at suspected reinfection (36/315, 11.4%) than initial infection (4094/75 149, 5.4%). Suspected reinfection rates were higher in females (1.0%, CI 0.8-1.2% versus 0.7%, CI 0.5-0.9%, p 0.002) and immunocompromised patients (2.1%, CI 1.0-4.2% versus 0.8%, CI 0.7-1.0%, p 0.004), and lower in children than adults (0.2%, CI 0.1-0.4% versus 0.9%, CI 0.7-1.0%, p 0.023). Patients hospitalized at initial infection were more likely to have suspected reinfection (1.2%, CI 0.6-1.7% versus 0.8%, CI 0.7-1.0%, p 0.030), as were those with initial infections later in 2020 (150-day incidence 0.4%, CI 0.2-0.5% September-October versus 0.2%, CI 0.1-0.3% March-May and 0.3%, CI 0.2-0.3% June-August, p 0.008). In an adjusted Cox proportional hazards model, being female (hazard ratio (HR) 1.44, CI 1.14-1.81), adult (age 18-39, HR 2.71, CI 1.38-5.31, age 40-59 HR 2.22, CI 1.12-4.41, age ≥60 HR 2.52, CI 1.23-5.17 versus <18 years), immunocompromised (HR 2.48, CI 1.31-4.68), hospitalized (HR 1.60, CI 1.07-2.38), and initially infected later in 2020 (HR 2.26, CI 1.38-3.71 September-October versus March-May) were significant independent predictors of suspected reinfection.

Conclusions: Reinfection with SARS-CoV-2 is uncommon, with suspected reinfections more likely in women, adults, immunocompromised subjects, and those previously hospitalized for coronavirus 2019 (COVID-19). This suggests a need for continued precautions and vaccination in patients with COVID-19 to prevent reinfection.