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Slezak J, Bruxvoort K, Fischer H, et al. Rate and severity of suspected SARS-Cov2 reinfection in a cohort of PCR-positive COVID-19 patients. Clin Microbiol Infect. 2021 Jul 28. pii: S1198-743X(21)00422-5. doi: 10.1016/j.cmi.2021.07.030. (Original study)

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.

Discipline Area Score
General Internal Medicine-Primary Care(US) 6 / 7
Family Medicine (FM)/General Practice (GP) 6 / 7
Pediatric Hospital Medicine 6 / 7
Hospital Doctor/Hospitalists 5 / 7
Internal Medicine 5 / 7
Infectious Disease 5 / 7
Pediatric Emergency Medicine 5 / 7
Emergency Medicine 5 / 7
Comments from MORE raters

Emergency Medicine rater

As subsequent waves of COVID-19 wash across the globe, understanding the epidemiology of reinfection is increasingly important. This primarily Hispanic California-based cohort exploring subsequent COVID-19 infections after SARS-CoV-2 emerged in March 2020 provides a glimpse at reinfections in the (mostly) pre-vaccinated world. As variants of COVID-19 emerge (such as the current delta version) that are more contagious and as increasing proportions of the population become immunized (hopefully), understanding reinfections and subsets at most risk of reinfection will likely need to be updated with more research.

Family Medicine (FM)/General Practice (GP) rater

These are very helpful data but I wonder how they will hold up with with the delta variant.

Family Medicine (FM)/General Practice (GP) rater

We are aware of the potential for re-infection, but good to have an estimate of 0.8% cumulative reinfection at 270 days.

Hospital Doctor/Hospitalists rater

In this large California database, reinfection rates for COVID were retrospectively described to be about 0.8% of their database. Women and minority populations as well as immunocompromised persons had higher rates. Unfortunately, this study was performed before widespread vaccination, so the effects of vaccination could not be analyzed for protection in this group.

Infectious Disease rater

This large cohort confirms what we already knew: reinfection is possible but unlikely.

Internal Medicine rater

These are quantitative estimates of the re-infection rate, which are a good thing, I am not sure how much this knowledge will influence practice. The data came from the pre-delta period and the infection rates are likely to be higher now.

Pediatric Hospital Medicine rater

A retrospective study of a cohort infected with SARS-COV-2 that shows that reinfection is uncommon (< by 270 days). This is a select population, however, and it is unclear which variants were responsible for the initial infection and the re-infection, and what effect vaccinations would have on the reinfections.
Comments from EvidenceAlerts subscribers

Dr. Barrie McLeod (9/2/2021 10:53 AM)

No one has yet commented on the increased rate of hospitalization in those reinfected. The implications of this observation is not explored. Given the title of the article, a little more exploration would be appreciated. Fortunately, reinfection is rare.