{"doi":"10.1371/journal.pone.0252235","title":"Seroprevalence of SARS-CoV-2 antibodies in Seattle, Washington: October 2019–April 2020","abstract":"BACKGROUND: The first US case of SARS-CoV-2 infection was detected on January 20, 2020. However, some serology studies suggest SARS-CoV-2 may have been present in the United States prior to that, as early as December 2019. The extent of domestic COVID-19 detection prior to 2020 has not been well-characterized. OBJECTIVES: To estimate the prevalence of SARS-CoV-2 antibody among healthcare users in the greater Seattle, Washington area from October 2019 through early April 2020. STUDY DESIGN: We tested residual samples from 766 Seattle-area adults for SARS-CoV-2 antibodies utilizing an ELISA against prefusion-stabilized Spike (S) protein. RESULTS: No antibody-positive samples were found between October 2, 2019 and March 13, 2020. Prevalence rose to 1.2% in late March and early April 2020. CONCLUSIONS: The absence of SARS-CoV-2 antibody-positive samples in October 2019 through mid-March, 2020, provides evidence against widespread circulation of COVID-19 among healthcare users in the Seattle area during that time. A small proportion of this metropolitan-area cohort had been infected with SARS-CoV-2 by spring of 2020.","journal":"PLoS ONE","year":2021,"id":211108,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":2,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9501,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2021-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":233085,"name":"Michael L. Jackson","orcid":"0000-0002-2340-0256","position":1,"is_corresponding":false},{"id":316704,"name":"James P. Hughes","orcid":"0000-0001-5034-3157","position":2,"is_corresponding":false},{"id":243265,"name":"Sandra Lester","orcid":"0000-0002-3829-365X","position":3,"is_corresponding":false},{"id":243264,"name":"Lisa Mills","orcid":"0000-0001-5674-9166","position":4,"is_corresponding":false},{"id":243266,"name":"Brandi Freeman","orcid":"0000-0002-9242-9562","position":5,"is_corresponding":false},{"id":800006,"name":"Mohammad Rasheed","orcid":"0000-0003-0038-6401","position":6,"is_corresponding":false},{"id":225078,"name":"Natalie J. Thornburg","orcid":"0000-0003-3523-3616","position":7,"is_corresponding":false},{"id":103432,"name":"Helen Y. Chu","orcid":"0000-0001-8502-9600","position":8,"is_corresponding":false},{"id":108420,"name":"Denise J. McCulloch","orcid":"0000-0001-8755-6105","position":0,"is_corresponding":true}],"reference_count":19,"raw_metadata":null,"created_at":"2026-07-18T23:52:16.049481Z","pmid":"34043706","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}