Citywide serosurveillance of the initial SARS-CoV-2 outbreak in San Francisco

Abstract

Serosurveillance provides a unique opportunity to quantify the proportion of the population that has been exposed to pathogens. Here, we developed and piloted Serosurveillance for Continuous, ActionabLe Epidemiologic Intelligence of Transmission (SCALE-IT), a platform through which we systematically tested remnant samples from routine blood draws in two major hospital networks in San Francisco for SARS-CoV-2 antibodies during the early months of the pandemic. Importantly, SCALE-IT allows for algorithmic sample selection and rich data on covariates by leveraging electronic medical record data. We estimated overall seroprevalence at 4.2%, corresponding to a case ascertainment rate of only 4.9%, and identified important heterogeneities by neighborhood, homelessness status, and race/ethnicity. Neighborhood seroprevalence estimates from SCALE-IT were comparable to local community-based surveys, while providing results encompassing the entire city that have been previously unavailable. Leveraging this hybrid serosurveillance approach has strong potential for application beyond this local context and for diseases other than SARS-CoV-2.

SARS-CoV-2 Cumulative Incidence and Period Seroprevalence: Results From a Statewide Population-Based Serosurvey in California

“…Results from this study indicated large disparities in burden of infection among Californians, particularly among Hispanic/Latinx persons compared with non-Hispanic/Latinx White persons. These data support other findings in California, which have documented seroprevalence up to 3 times as high among Hispanic/Latinx persons compared with non-Hispanic/Latinx White persons [ 6 , 22 , 23 ]. We also reported differences in seroprevalence by insurance status and workplace.…”

“…The estimated IFR was 0.8% for adults, and we found that only 1 in 3 SARS-CoV-2 infections in adults was reported to the CDPH through early November 2020. Disparities documented in our study by ethnicity and insurance status may be larger than previously suggested by local seroprevalence studies [ 6 , 23 ] and surveillance data [ 28 ]. Taken together, these data underscore the continued need to focus public health interventions, including access to testing and vaccination in socioeconomically vulnerable communities, which are the most heavily impacted.…”

“…This is consistent with previous reports of varying seroprevalence by social determinants of health such as household income and housing status [ 2 , 22 ] and parallels inequities seen among PCR-confirmed cases [ 24 ]. Socioeconomic factors including essential worker status and ability to physically distance from others while at work or home are associated with risk for SARS-CoV-2 infection; therefore, a continued focus on health equity in California’s vaccine distribution is essential [ 23 ].…”

Using sero-epidemiology to monitor disparities in vaccination and infection with SARS-CoV-2

“…To measure disparities in both infection rates and vaccination, we leveraged a SARS-CoV-2 serosurveillance platform launched in March 2020 that utilizes residual blood samples taken from two hospital networks in San Francisco. Estimates derived from this platform during the first wave of the pandemic showed seroprevalence in Latinx individuals to be nearly two times higher than in white individuals, and nearly two times higher in homeless individuals than the population average (9). We collected samples from 1,014 individuals undergoing routine blood draws between February 4 and February 17, 2021, capturing transmission during the first 11 months of the epidemic and the early roll-out of vaccination.…”

Prevalence and Correlates of SARS CoV-2 Among a Community-Based Sample Recruited Using Randomized Venue-Based Sampling. Essex County, NJ, 2020

“…At the time of testing, dried blood from the Mitra device was eluted overnight at 4 °C, based on published protocols [24]. The eluate was diluted with 2% non-fat dry milk to1:80 and utilized for detection of IgG antibodies to recombinant receptor binding domain (RBD) of the SARS-CoV-2 Spike (100 ng/well), utilizing standard enzyme-linked immunosorbent assay (ELISA) protocols [25,26]. To interpret the ELISA data, we calculated a cut off of OD 405 = 0.3 (mean + 3 standard deviations) by testing finger-stick eluates from 50 COVID-19 PCR-negative subjects.…”