Cycle Threshold Values of SARS-CoV-2 RT-PCR during Outbreaks in Nursing Homes: A Retrospective Cohort Study

• Published in: Epidemiolgia (Basel, Switzerland) Switzerland), 2024-10, Vol.5 (4), p.658-668
• Main Authors: Gascó-Laborda, Juan Carlos, Gil-Fortuño, Maria, Tirado-Balaguer, Maria Dolores, Meseguer-Ferrer, Noemi, Sabalza-Baztán, Oihana, Pérez-Olaso, Óscar, Gómez-Alfaro, Iris, Poujois-Gisbert, Sandrine, Hernández-Pérez, Noelia, Lluch-Bacas, Lledó, Rusen, Viorica, Arnedo-Pena, Alberto, Bellido-Blasco, Juan Bautista
• Format: Article
• Language: English
• ISSN: 2673-3986; 2673-3986
• DOI: 10.3390/epidemiologia5040046

Backgound/Objectives: Cycle threshold (Ct) values of SARS-CoV-2 real-time reverse transcriptase-polymerase chain reaction (RT-PCR) tests are associated with infectivity and viral load, and they could be an aid in forecasting the evolution of SARS-CoV-2 outbreaks. The objective was to know the Ct values related to the incidence and reinfection of SARS-CoV-2 in successive outbreaks, which took place in nursing homes in Castellon (Spain) during 2020-2022, and to test its usefulness as an instrument of epidemic surveillance in nursing homes. a retrospective cohort design with Poisson regression and multinomial logistic regression were used. We studied four nursing home SARS-CoV-2 outbreaks, and the average infection rate, reinfection rate, and case fatality were 72.7%, 19.9%, and 5.5%, respectively; 98.9% of residents were vaccinated with three doses of a mRNA SARS-CoV-2 vaccine. Ct values for first infections and reinfections were 27.1 ± 6.6 and 31.9 ± 5.4 ( = 0.000). Considering Ct values ≥ 30 versus