COVID infection rates, clinical outcomes, and racial/ethnic and gender disparities before and after Omicron emerged in the US

  1. Lindsey Wang
  2. Nathan A. Berger
  3. David C. Kaelber
  4. Pamela B. Davis
  5. Nora D. Volkow
  6. Rong Xu

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Abstract

Background

SARS-CoV-2 infections and hospitalizations are rising in the US and other countries after the emergence of the Omicron variant. Currently, data on infection rates, severity and racial/ethnic and gender disparities from Omicron in the US is limited.

Method

We performed a retrospective cohort study of a large, geographically diverse database of patient electronic health records (EHRs) in the US. The study population comprised 881,473 patients who contracted SARS-CoV-2 infection for the first time between 9/1/2021-1/16/2022, including 147,964 patients infected when Omicron predominated (Omicron cohort), 633,581 when Delta predominated (Delta cohort) and another 99,928 infected when the Delta predominated but just before the Omicron variant was detected in the US (Delta-2 cohort). We examined monthly incidence rates of COVID-19 infections stratified by age groups, gender, race and ethnicity, compared severe clinical outcomes including emergency department (ED) visits, hospitalizations, intensive care unit (ICU) admissions, and mechanical ventilation use between propensity-score matched Omicron and Delta cohorts stratified by age groups (0-4, 5-17, 18-64 and ≥ 65 years), and examined racial/ethnic and gender differences in severe clinical outcomes.

Findings

Among 147,964 infected patients in the Omicron cohort (average age: 39.1 years), 56.7% were female, 2.4% Asian, 21.1% Black, 6.2% Hispanic, and 51.8% White. The monthly incidence rate of COVID infections (new cases per 1000 persons per day) was 0.5-0.7 when Delta predominated, and rapidly increased to 3.8-5.2 when Omicron predominated. In January 2022, the infection rate was highest in children under 5 years (11.0) among all age groups, higher in Black than in White patients (14.0 vs. 3.8), and higher in Hispanic than in non-Hispanic patients (8.9 vs. 3.1). After propensity-score matching for demographics, socio-economic determinants of health, comorbidities and medications, risks for severe clinical outcomes in the Omicron cohort were significantly lower than in the Delta cohort: ED visits: 10.2% vs. 14.6% (risk ratio or RR: 0.70 [0.68-0.71]); hospitalizations: 2.6% vs. 4.4% (RR: 0.58 [0.55-0.60]); ICU admissions: 0.47% vs. 1.00% (RR: 0.47 [0.43-0.51]); mechanical ventilation: 0.08% vs. 0.3% (RR: 0.25 [0.20-0.31]). Similar reduction in disease severity was observed for all age groups. There were significant racial/ethnic and gender disparities in severe clinical outcomes in the Omicron cohort, with Black, Hispanic patients having more ED visits and ICU admissions than White and non-Hispanic patients, respectively and women had fewer hospitalization and ICU admission than men.

Interpretation

The incidence rate of COVID infection during the omicron predominant period (prevalence >92%) was 6-8 times higher than during the Delta predominant period that preceded it consistent with greater infectivity. The incidence rate was highest among those less than 5 years of age, and in Black and Hispanic patients. COVID infections occurring when the Omicron predominated were associated with significantly less frequent severe outcomes than in matched patients when the Delta variant predominated. There were significant racial, ethnic and gender disparities in severe clinical outcomes, with Black and Hispanic patients and men disproportionally impacted.

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    SciScore for 10.1101/2022.02.21.22271300: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    EthicsIRB: Because this study only queried statistics of de-identified patient records through web-applications and did not involve retrieval, storage, collection, use, or transmittal of individually identifiable data, Institutional Review Board approval and informed consent was not needed or sought.
    Consent: Because this study only queried statistics of de-identified patient records through web-applications and did not involve retrieval, storage, collection, use, or transmittal of individually identifiable data, Institutional Review Board approval and informed consent was not needed or sought.
    Sex as a biological variableRacial, ethnic and gender disparities were examined by comparing clinical outcomes (ED visits, hospitalization, ICU admission) in the 3-day time-window that followed from the first day of SARS-CoV-2 infection between matched Black and White patients, between matched Hispanic and non-Hispanic patients, and between women and men, for the Omicron, Delta, and Delta-2 cohort respectively.
    Randomizationnot detected.
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    The two cohorts were propensity-score matched (1:1 using a nearest neighbor greedy matching with a caliper of 0.25 times the standard deviation) for demographics (age, gender, race/ethnicity); adverse socioeconomic determinants of health (assessed by ICD-10 codes “Z55-Z65” for “Persons with potential health hazards related to socioeconomic and psychosocial circumstances”) that include employment, housing, education, and economic circumstances; comorbidities relevant to COVID-19 risks or outcomes(7,8) including hypertension, heart diseases, cerebrovascular diseases, cancer, obesity, type 2 diabetes, chronic respiratory diseases, chronic kidney diseases, liver diseases, HIV infection, dementia, substance use disorders, depression and anxiety (assessed by ICD-10 codes); behavioral factors (tobacco smoking, alcohol drinking) (assessed by one or more encounter based on ICD-10 codes); COVID-19-related medications(9) (assessed by RxNorm codes); and vaccination status documented in patient EHRs (assessed by CPT or RxNorm codes).
    RxNorm
    suggested: (RxNorm, RRID:SCR_006645)

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Our study has several limitations: First, the observational, retrospective nature of this study of patient EHR data could introduce case selection biases, over representation of symptomatic testing, reporting and follow up issues. However, because we compared the different cohort populations all from the TriNetX dataset, these issues should not substantially affect the relative risk analyses. Second, patients in the TriNetX EHR database are those who had medical encounters with healthcare systems contributing to the TriNetX Platform and do not necessarily represent the entire US population. Therefore, results from the TriNetX platform need to be validated in other populations. Third, both the Omicron and Delta cohorts in our study were defined based on CDC’s national genomic sequence surveillance and not by variant identification in individual patients. Therefore, the Omicron cohort likely contained a few infections with the Delta variant. However, our findings of reduced disease severity in the Omicron cohort compared to the Delta cohort are consistent with findings from Africa(2), Scotland(3), and England(4) that were based on individual genomic sequences. The fact that no reduction in severe disease frequency was observed between the two Delta cohorts further suggest that the differences resulted from inherent properties of the variant itself. Moreover the increase in severity outcomes for the Delta-2 compared to the Delta cohort, if anything, points to waning immunity fro...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

    About SciScore

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  2. Version published to 10.1101/2022.02.21.22271300v1 on medRxiv