Association of Culturable-Virus Detection and Household Transmission of SARS-CoV-2, California and Tennessee, 2020-2022

Abstract

From 2 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) household transmission studies (enrolling April 2020 to January 2022) with rapid enrollment and specimen collection for 14 days, 61% (43/70) of primary cases had culturable virus detected ≥6 days post-onset. Risk of secondary infection among household contacts tended to be greater when primary cases had culturable virus detected after onset. Regardless of duration of culturable virus, most secondary infections (70%, 28/40) had serial intervals <6 days, suggesting early transmission. These data examine viral culture as a proxy for infectiousness, reaffirm the need for rapid control measures after infection, and highlight the potential for prolonged infectiousness (≥6 days) in many individuals.

Keywords: SARS-CoV-2; household transmission; secondary infection risk; viral culture.

Figure 1.

SARS-CoV-2 primary case daily culture status and timing of secondary infections from date of primary case illness onset through follow-up—household transmission studies in TN and CA, 2020–2022. Viral culture was performed on nasal specimens that met the following characteristics: (1) Nashville, TN, all SARS-CoV-2 RT-qPCR–positive (Ct < 40) specimens; and (2) San Francisco, CA, all SARS-CoV-2 RT-qPCR–positive (Ct < 40 for 2 gene targets, N and E) specimens up to day 14. After 14 days, SARS-CoV-2 RT-qPCR–positive (Ct < 40 for 2 gene targets, N and E) specimens were cultured until 3 consistent negative cultures were observed. Each asterisk (*) indicates days during follow-up when a household contact with SARS-CoV-2 infection had illness onset. Abbreviations: Ct, cycle threshold; RT-qPCR, reverse transcription quantitative polymerase chain reaction; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.