Overall seroprevalence of SARS-CoV-2 antibodies relatively low in the USA adult and dialysis populations

1. The standardized seroprevalence of SARS-CoV-2 antibodies in the US population was estimated to be 9.3% with significant regional variation.

2. Higher rates of seropositivity were seen in residents of non-Hispanic Black and Hispanic neighborhoods, as well as neighborhoods in the highest population density quintile.

Evidence Rating Level: 3 (Average)

Study Rundown: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus, the causative agent of COVID-19, stimulates a rapid antibody response in both symptomatic and asymptomatic individuals. Given the scale of the pandemic, accurately estimating the seroprevalence of SARS-CoV-2 antibodies in the population is critical to estimate rates of exposure and spread of the virus. However, most studies estimating seroprevalence to date have been restricted to specific hotspots or populations with poor longitudinal follow-up. This cross-sectional study utilized a SARS-CoV-2 spike protein receptor binding domain (S1RBD) total antibody chemiluminescence assay to analyze samples obtained from patients undergoing dialysis across the USA. Overall, standardized seroprevalence of SARS-CoV-2 antibodies in the US population was estimated to be 9.3% with significant regional variation. Regional seroprevalence was lowest in the west and highest in the northeastern states. Other factors associated with higher seroprevalence included race and ethnicity with highest rates in non-Hispanic black and Hispanic patients followed by non-Hispanic white patients having the lowest rates. A major strength of the study comes from the large sample size and sample scheme allowing for estimates of seroprevalence with high precision. However, it is plausible that seroprevalence estimates from the US dialysis population overestimate seroprevalence compared to the general US population. Additionally, there may be an under-representation of patients living in rural areas as dialysis units are more often located in urban centers and public transportation has been less accessible in the current pandemic.

Click to read the study in The Lancet

Relevant Reading: Prevalence of SARS-CoV-2 in Spain (ENE-COVID): a nationwide, population-based seroepidemiological study

In-Depth [cross-sectional study]: This national, cross-sectional study included 28,503 adults (age ≥18, 57.4% male) receiving dialysis in July 2020 with plasma samples obtained from approximately 1300 dialysis facilities across the USA. Samples were analyzed with a SARS-CoV-2 spike protein receptor binding domain total antibody chemiluminescence assay (100% sensitivity, 99.8% specificity) and data was correlated with age, sex, region, and race and ethnicity information gathered from anonymized electronic health records.

Overall seroprevalence of SARS-CoV-2 was 8.0% (95% CI 7.7 to 8.4) in the sample population and 9.3% (95% CI 8.8 to 9.9) when standardized to the US adult population. When standardized to the US dialysis population, there was significant regional variance in seroprevalence ranging from 3.5% (95% CI 3.1 to 3.9) in the west to 27.2% (95% CI 25.9 to 28.5) in the northeast. In comparison to the estimated seropositivity rate of 8989 per 100,000 population, the prevalence of nasopharyngeal swab diagnosed cases at the same time was 826 per 100,000 meaning that 9.2% (95% CI 8.7 to 9.8) of seropositive individuals were diagnosed. Likelihood of SARS-CoV-2 seropositivity was lower amongst older individuals (>80 years) versus people aged 45-64 years (odds ratio 0.8, 95% CI 0.7 to 0.9) but did not differ by gender (odds ratio 1.0, 95% CI 0.9 to 1.1) for women versus men. Non-Hispanic black patients had the highest rates of seropositivity in the sample population (14.7%, 95% CI 13.3 to 16.3) followed by Hispanic patients (9%, 95% CI 8.2 to 10.0) and non-Hispanic white patients (4.2%, 95% CI 3.8 to 4.7). Serial sampling of dialysis patients may be a viable way to determine trends in disease prevalence and effectiveness of management strategies as the COVID-19 pandemic continues to evolve.

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