Rapid antigen tests, such as the Abbott BinaxNOW COVID-19 Ag Card (BinaxNOW), offer results more rapidly (approximately 15-30 minutes) and at a lower cost than do highly sensitive nucleic acid amplification tests (NAATs) (1). Rapid antigen tests have received Food and Drug Administration (FDA) Emergency Use Authorization (EUA) for use in symptomatic persons (2), but data are lacking on test performance in asymptomatic persons to inform expanded screening testing to rapidly identify and isolate infected persons (3). To evaluate the performance of the BinaxNOW rapid antigen test, it was used along with real-time reverse transcription-polymerase chain reaction (RT-PCR) testing to analyze 3,419 paired specimens collected from persons aged ≥10 years at two community testing sites in Pima County, Arizona, during November 3-17, 2020. Viral culture was performed on 274 of 303 residual real-time RT-PCR specimens with positive results by either test (29 were not available for culture). Compared with real-time RT-PCR testing, the BinaxNOW antigen test had a sensitivity of 64.2% for specimens from symptomatic persons and 35.8% for specimens from asymptomatic persons, with near 100% specificity in specimens from both groups. Virus was cultured from 96 of 274 (35.0%) specimens, including 85 (57.8%) of 147 with concordant antigen and real-time RT-PCR positive results, 11 (8.9%) of 124 with false-negative antigen test results, and none of three with false-positive antigen test results. Among specimens positive for viral culture, sensitivity was 92.6% for symptomatic and 78.6% for asymptomatic individuals. When the pretest probability for receiving positive test results for SARS-CoV-2 is elevated (e.g., in symptomatic persons or in persons with a known COVID-19 exposure), a negative antigen test result should be confirmed by NAAT (1). Despite a lower sensitivity to detect infection, rapid antigen tests can be an important tool for screening because of their quick turnaround time, lower costs and resource needs, high specificity, and high positive predictive value (PPV) in settings * Specimens were used to perform a limiting-dilution inoculation of Vero CCL-81 cells, and cultures showing evidence of cytopathic effect were tested by real-time RT-PCR for the presence of SARS-CoV-2 RNA. Viral recovery was defined as any culture in which the first passage had an N1 Ct value at least two Ct values lower than the corresponding clinical specimen. † https://www.biorxiv

this report was posted as an MMWR Early Release on the MMWR website (https://www.cdc.gov/mmwr).Transmission of SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), is ongoing in many communities throughout the United States. Although case-based and syndromic surveillance are critical for monitoring the pandemic, these systems rely on persons obtaining testing or reporting a COVID-19-like illness. Using serologic tests to detect the presence of SARS-CoV-2 antibodies is an adjunctive strategy that estimates the prevalence of past infection in a population. During April 28-May 3, 2020, coinciding with the end of a statewide shelter-in-place order, CDC and the Georgia Department of Public Health conducted a serologic survey in DeKalb and Fulton counties in metropolitan Atlanta to estimate SARS-CoV-2 seroprevalence in the population. A two-stage cluster sampling design was used to randomly select 30 census blocks in each county, with a target of seven participating households per census block. Weighted estimates were calculated to account for the probability of selection and adjusted for age group, sex, and race/ethnicity. A total of 394 households and 696 persons participated and had a serology result; 19 (2.7%) of 696 persons had SARS-CoV-2 antibodies detected. The estimated weighted seroprevalence across these two metropolitan Atlanta counties was 2.5% (95% confidence interval [CI] = 1.4-4.5). Non-Hispanic black participants more commonly had SARS-CoV-2 antibodies than did participants of other racial/ethnic groups (p<0.01). Among persons with SARS-CoV-2 antibodies, 13 (weighted % = 49.9; 95% CI = 24.4-75.5) reported a COVID-19-compatible illness,* six (weighted % = 28.2; 95% CI = 11.9-53.3) sought medical care for a COVID-19-compatible illness, and five (weighted % = 15.7; 95% CI = 5.1-39.4) had been tested for SARS-CoV-2 infection, demonstrating that many of these infections would not have been identified through case-based

IMPORTANCEAs self-collected home antigen tests become widely available, a better understanding of their performance during the course of SARS-CoV-2 infection is needed. OBJECTIVE To evaluate the diagnostic performance of home antigen tests compared with reverse transcription-polymerase chain reaction (RT-PCR) and viral culture by days from illness onset, as well as user acceptability. DESIGN, SETTING, AND PARTICIPANTS This prospective cohort study was conducted from January to May 2021 in San Diego County, California, and metropolitan Denver, Colorado. The convenience sample included adults and children with RT-PCR-confirmed infection who used self-collected home antigen tests for 15 days and underwent at least 1 nasopharyngeal swab for RT-PCR, viral culture, and sequencing. EXPOSURES SARS-CoV-2 infection. MAIN OUTCOMES AND MEASURES The primary outcome was the daily sensitivity of home antigen tests to detect RT-PCR-confirmed cases. Secondary outcomes included the daily percentage of antigen test, RT-PCR, and viral culture results that were positive, and antigen test sensitivity compared with same-day RT-PCR and cultures. Antigen test use errors and acceptability were assessed for a subset of participants. RESULTS This study enrolled 225 persons with RT-PCR-confirmed infection (median [range] age, 29 [1-83] years; 117 female participants [52%]; 10 [4%] Asian, 6 [3%] Black or African American, 50 [22%] Hispanic or Latino, 3 [1%] Native Hawaiian or Other Pacific Islander, 145[64%] White, and 11 [5%] multiracial individuals) who completed 3044 antigen tests and 642 nasopharyngeal swabs. Antigen test sensitivity was 50% (95% CI, 45%-55%) during the infectious period, 64% (95% CI, 56%-70%) compared with same-day RT-PCR, and 84% (95% CI, 75%-90%) compared with same-day cultures. Antigen test sensitivity peaked 4 days after illness onset at 77% (95% CI, 69%-83%). Antigen test sensitivity improved with a second antigen test 1 to 2 days later, particularly early in the infection. Six days after illness onset, antigen test result positivity was 61% (95% CI, 53%-68%). Almost all (216 [96%]) surveyed individuals reported that they would be more likely to get tested for SARS-CoV-2 infection if home antigen tests were available over the counter. CONCLUSIONS AND RELEVANCEThe results of this cohort study of home antigen tests suggest that sensitivity for SARS-CoV-2 was moderate compared with RT-PCR and high compared with viral culture. The results also suggest that symptomatic individuals with an initial negative home antigen test result for SARS-CoV-2 infection should test again 1 to 2 days later because test sensitivity peaked several days after illness onset and improved with repeated testing.

Dried blood spots (DBS) expedite the collection, storage and shipping of blood samples, thereby facilitating large-scale serologic studies. We evaluated the sensitivity of anti-HCV IgG testing and HCV-RNA quantitation using freshly prepared and stored DBS derived from HCV-infected patients. Protocols for elution were optimized using DBS prepared from plasma of 52 HCV-infected persons and 51 uninfected persons (control DBS), then applied to DBS from 33 chronic hepatitis C patients that had been stored at -20°C for 5 years (stored DBS). Control and stored DBS, and their corresponding plasma, were processed for anti-HCV IgG testing using the VITROS chemiluminescence assay (CIA) and the HCV 3.0 enzyme immunoassay (EIA) (Ortho-Clinical Diagnostics), and for HCV RNA quantitation by quantitative (q) RT-PCR. HCV genotyping was conducted by nucleotide sequencing. The sensitivity of CIA and EIA in control DBS was 92% and 90%, respectively, compared to 100% and 97%, respectively, in stored DBS. The sensitivity of HCV RNA detection was 88% in control DBS, compared to 36% in stored DBS. Specificity was 100% for all the assays in both control and stored DBS. Genotypes 1, 2 and 3 were detected in 16 (62%), 6 (23.1%), and 4 (15.3%) samples, respectively. Sequences generated from DBS and their corresponding plasma samples were identical. Whereas the sensitivity of anti-HCV IgG detection in stored DBS was equivalent to that in recently prepared DBS, the sensitivity of HCV RNA detection was markedly lower in stored DBS compared to recently prepared DBS. Stored DBS may be reliably used for anti-HCV detection but for HCV-RNA-based testing freshly prepared DBS is preferable to stored DBS.

Hepatitis E is a major public health problem in developing countries and is increasingly being recognized as a cause of substantial sporadic viral hepatitis infections in industrialized countries. Variable rates of hepatitis E seroprevalence have been reported from the same geographic regions depending on the assay used. In this study, we evaluated the performance characteristics of four assays which included two commercial assays, Wantai HEV-IgG ELISA kit (Wantai, China), and DS-EIA-ANTI-HEV-G kit (DSI, Italy), one NIH-developed immunoassay (NIH-55 K, Kuniholm et al. [2009] Journal of Infectious Diseases 200:48-56), previously used in several major seroprevalence studies and one in-house Western blot assay (CDC-WB). The limit of detection of IgG anti-HEV is 100 mIU/mL for Wantai assay, 200 mIU/mL for CDC-WB assay, 1000 mIU/mL for DSI assay, and 40 mIU/mL for NIH-55 K assay. Pairwise concordance between the four assays ranged from 56% to 87%. The concordance among all four assays was observed in 52% of the samples, while the concordance among three assays was observed in 37% of the samples. These data show a wide discordance between various IgG anti-HEV assays and warrant a comprehensive evaluation of all the assays using well characterized global serum reference panels.