Viral culture and immunofluorescence for the detection of SARS-CoV-2 infectivity in RT-PCR positive respiratory samples

Carla Berengua*, Marina López, Montserrat Esteban, Pilar Marín, Paula Ramos, Margarita del Cuerpo, Ignasi Gich, Ferran Navarro, Elisenda Miró, Núria Rabella

*Autor correspondiente de este trabajo

Producción científica: Contribución a una revistaArtículoInvestigaciónrevisión exhaustiva

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Resumen

Background: Knowing how long SARS-CoV-2-positive individuals can remain infective is crucial for the design of infection prevention and control strategies. Viral culture is the gold standard for detecting an active-replicative virus and evaluating its infectious potential. Objective: To assess the correlation of SARS-CoV-2 infectivity with the number of days from symptom onset and the Ct value, using culture as a reference method. Also, to describe a detailed protocol for SARS-CoV-2 culture and immunofluorescence confirmation based on our experience with other respiratory viruses. Study design: 100 consecutive respiratory samples positive for SARS-CoV-2 by RT-PCR from different subjects were inoculated into VERO E6 cells. Results: Viral isolation was successful in 58% of samples. The median number of days from symptom onset for culture-positive samples was 2, and 15 for culture-negative samples. Six positive cultures were obtained in patients ≥14 days after symptom onset, all of whom were immunocompromised or with severe COVID-19. The mean Ct value was 12.64 units higher in culture-negative than in culture-positive samples. The probability of successfully isolating SARS-CoV-2 in samples with a Ct value <22 was 100%, decreasing to 3.1% when >27. Conclusions: Our findings show a significant positive correlation between the probability of isolating SARS-CoV-2 in culture, fewer days of symptoms and a lower RT-PCR Ct value. SARS-CoV-2 infectivity lasts no more than 14 days from symptom onset in immunocompetent individuals. In contrast, in immunocompromised patients or those with severe COVID-19 infectivity may remain after 14 days. Ct value <22 always indicates infectivity.

Idioma originalInglés
Número de artículo105167
Número de páginas6
PublicaciónJournal of Clinical Virology
Volumen152
DOI
EstadoPublicada - jul 2022

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