Rate and severity of suspected SARS-Cov2 reinfection in a cohort of PCR-positive COVID-19 patients.

OBJECTIVES: To estimate the burden and severity of suspected SARS-CoV2 reinfection. METHODS: A retrospective cohort of members of Kaiser Permanente Southern California with PCR-positive SARS-CoV2 infection between 3/1/2020 and 10/31/2020 was followed through electronic health records for subsequent positive SARS-CoV2 tests (suspected reinfection) >90 days after initial infection, through 1/31/2021. 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 (49648/75149, 66.1%), with slightly more females (39736, 52.9%) than males, and few immunocompromised patients (953, 1.3%). There were 315 suspected reinfections identified, with 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 (4094/75149, 5.4%). Suspected reinfection rates were higher in females (1.0%, CI=0.8-1.2% vs 0.7%, CI=0.5-0.9%, p=0.002) and immunocompromised patients (2.1%, CI=1.0-4.2% vs 0.8%, CI=0.7-1.0%, p=0.004), and lower in children than adults (0.2%, CI=0.1-0.4% vs 0.9%, CI=0.7-1.0%, p=.023). Patients hospitalized at initial infection were more likely to have suspected reinfection (1.2%, CI=0.6-1.7% vs 0.8%, CI=0.7-1.0%, p=.030), as were those with initial infections later in 2020 (150-day incidence 0.4%, CI=0.2-0.5% September-October vs 0.2%, CI=0.1-0.3% March-May and 0.3%, CI=0.2-0.3% June-August, p=.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=1.12-4.4, age >60 HR=2.52, CI=1.23-5.17 vs <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 vs March-May) were significant independent predictors of suspected reinfection. CONCLUSIONS: Reinfection with SARS-CoV2 is uncommon, with suspected reinfections more likely in women, adults, immunocompromised, and those previously hospitalized for COVID-19. This suggests a need for continued precautions and vaccination in patients with COVID-19 to prevent reinfection.