Volume 27, Number 1—January 2021
Racial and Workplace Disparities in Seroprevalence of SARS-CoV-2, Baton Rouge, Louisiana, USA
By using paired molecular and antibody testing for severe acute respiratory syndrome coronavirus 2 infection, we determined point prevalence and seroprevalence in Louisiana, USA, during the second phase of reopening. Infections were highly variable by race and ethnicity, work environment, and ZIP code. Census-weighted seroprevalence was 3.6%, and point prevalence was 3.0%.
We previously reported results from a seroprevalence study conducted in New Orleans, Louisiana, USA, which was hit hard early in the coronavirus disease (COVID-19) pandemic (1). Baton Rouge is a large metropolitan area roughly 80 miles northwest of New Orleans; at the time of this study, it was in the second phase of reopening after a stay-at-home order. Although the seroprevalence in New Orleans (6.9%) (1) was similar to prevalence recorded in Spain (5%), São Paulo, Brazil (4.7%), and New York, USA (6.9%) (2,3; B.H. Tess, unpub. data, https://doi.org/10.1101/2020.06.29.20142331), Baton Rouge had only 3,427 more cases as of August 2, 2020 (17,093 cases), than New Orleans did by May 16, 2020 (13,666 cases) (4). This latest study estimated severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in the greater Baton Rouge area (Ascension, East Baton Rouge, Livingston, and West Baton Rouge Parishes), with additional information on potential workplace exposures.
The protocol was approved by the Ochsner institutional review board and was designed to enroll and test <2,500 participants at 13 sites throughout Baton Rouge during July 15–31. Recruitment targeted a representative sample by using a method developed by Public Democracy (https://www.publicdemocracy.io) and described elsewhere (1,5). In contrast to the New Orleans study, in which persons tested were under a stay-at-home order, Baton Rouge was in phase 2 of reopening. A randomized subset of 500,000 Baton Rouge residents were targeted with digital ads for recruitment. Of those, 3,687 volunteers were recruited and restratified according to census designations; 2,309 were invited to participate, 2,179 enrolled and completed testing, and 2,138 were included in our final analysis. A total of 38 persons were excluded because they lived in ineligible ZIP codes, and 3 withdrew consent (Appendix). All study materials were provided in English, Spanish, and Vietnamese. Participants were offered free transportation. Research staff verbally obtained consent from participants and electronically documented consent and survey responses. We then procured blood samples and nasopharyngeal swab specimens from participants.
We used US Food and Drug Administration Emergency Use Authorization–approved tests. Real-time reverse transcription PCR of nasopharyngeal swab specimens was performed by using the Abbott m2000 RealTime system (Abbott, https://www.molecular.abbott). Qualitative IgG blood tests were performed by using the ARCHITECT i2000SR (Abbott). The IgG test meets criteria established by the Centers for Disease Control and Prevention to yield high positive predictive value, which was validated by Ochsner Health laboratory and others (6,7). Study participants who tested positive on either or both tests were assessed as having been infected with SARS-CoV-2. Point estimates and corresponding 95% CIs for proportions of SARS-CoV-2 exposure (PCR+ or IgG+ tests), point prevalence (PCR+, IgG–), and seroprevalence (IgG+ tests regardless of PCR test result) were estimated for the Baton Rouge area by using raw and census-weighted counts. Unadjusted odds ratios with Firth correction were calculated for all variables.
The sample was 63.6% female and 66.9% white; average age was 48.7 years (range 18–91) and average household size 2.84 persons. The census-weighted estimate of SARS-CoV-2 infections in the sample is 6.6% (6.0%, raw), with 3.0% positive for active viral shedding without detectable antibody, which translates to 16,536 contagious persons. By race and ethnicity, seroprevalence was highest (7.5%) in Black participants, compared with White non-Hispanic (1.8%), Asian non-Hispanic (1.7%), Hispanic of any race (1.6%), and other (2.7%) participants (Table).
The point prevalence and any SARS-CoV-2 infection were mapped by ZIP codes across the greater Baton Rouge area (Appendix). Point prevalence and all infections were highly variable by ZIP code.
Marital status was associated with prevalence (p = 0.0005 by χ2 test). Single persons had the highest rate of infection (9.3%), compared with rates for married or cohabitating participants (5.0%), and were 1.9 times more likely to test positive (Figure). Work environment also affected prevalence (p = 0.01 by χ2 test); the lowest prevalence was in participants who worked from home part-time and went to a workplace part-time (3.7%). Those who worked primarily outside the home had the highest prevalence (8.2%) and were 2.3 times more likely to test positive than those who worked from home at least part-time. Infection rates varied by occupation (p = 0.01 by χ2 test); the lowest positivity was in office workers (3.0%) and increased odds of testing positive occurred in delivery, healthcare, and other public-facing jobs. However, based on seroprevalence, which also varied substantially by occupation (p = 0.03 by χ2 test), healthcare workers and public-facing workers bore the brunt of early infections, as demonstrated by higher odds of testing positive for antibodies (Figure).
We found the prevalence of SARS-CoV-2 infection in Baton Rouge to be 6.6% but with a heavy concentration of new, contagious infections (3.0%). Persons who were infected early possibly no longer had antibodies. This finding differed from our New Orleans study, which was performed after extensive lockdowns and estimated new infections at 0.9% (1). Some populations had higher rates of infection than others, including Black and Hispanic communities and public-facing workers or those who do not work from home.
Dr. Feehan is a research scientist at the Ochsner Clinic Foundation’s Infectious Disease Clinical Research Department. Her research focuses on the gut microbiome as a treatment modality for neurologic disease, but more immediately on the COVID-19 pandemic.
The authors would like to especially thank the laboratories at the Ochsner Medical Center Jefferson Highway Campus for testing and keeping track of research samples; Christy Reeves for liaising with public leaders and sites; Eric Sapp and Dan Nichols for their recruitment effort; Susan Green, Charlene Ho, Lena Hooper, Patty Kline, and Candace Melancon for clinical site management; Johanna Veal, Lyndsey Buckner-Baiamonte, Ansley Hammons, and Ashley LaRoche for research site management; and countless research coordinators, clinical staff, marketing personnel, medical students, and Epic and IT staff for making site testing possible. The Ochsner Health Market Planning and Analysis team designed the maps in Appendix Figure 1. The authors thank Kathleen McFadden for her thorough editing. We would like to thank the Ochsner Language Services Department for helping to increase inclusivity and to acknowledge the East Baton Rouge Mayor–President Sharon Weston Broome and Pennington Biomedical Research Center for their collaboration and support of this project.
The study was funded by the Baton Rouge Area Foundation, Louisiana COVID-19 Health Equity Task Force, and the Humana Foundation, with additional support from the Blue Cross and Blue Shield of Louisiana Foundation, Healthy Blue, the Huey and Angelina Wilson Foundation, and the Irene W. and C.B. Pennington Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
- Feehan AK, Fort D, Garcia-Diaz J, Price-Haywood EG, Velasco C, Sapp E, et al. Seroprevalence of SARS-CoV-2 and infection fatality ratio, Orleans and Jefferson parishes, Louisiana, USA, May 2020. Emerg Infect Dis. 2020;26:2766–9.
- Pollán M, Pérez-Gómez B, Pastor-Barriuso R, Oteo J, Hernán MA, Pérez-Olmeda M, et al.; ENE-COVID Study Group. Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study. Lancet. 2020;396:535–44.
- Havers FP, Reed C, Lim T, et al. Seroprevalence of Antibodies to SARS-CoV-2 in 10 sites in the United States, March 23–May 12, 2020. JAMA Intern Med. 2020 Jul 21 [Epub ahead of print].
- Louisiana Department of Public Health. Louisiana coronavirus COVID-19 information [cited 2020 Sep 20]. http://ldh.la.gov/Coronavirus
- Feehan A, Fort D, Garcia-Diaz J, Price-Haywood E, Velasco C, Sapp E, et al. Frequency of symptoms and asymptomatic SARS-CoV-2 infection in New Orleans, Louisiana after 7 weeks of a stay-at-home order [cited 2020 Sep 8]. https://ssrn.com/abstract=3633166
- US Centers for Disease Control and Prevention. Interim guidelines for COVID-19 antibody testing [cited 2020 Aug 10]. https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antibody-tests-guidelines.html
- Bryan A, Pepper G, Wener MH, Fink SL, Morishima C, Chaudhary A, et al. Performance characteristics of the Abbott Architect SARS-CoV-2 IgG assay and seroprevalence in Boise, Idaho. J Clin Microbiol. 2020;58:e00941–20.