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Infectivity of SARS-CoV-2 on Inanimate Surfaces: Don't Trust Ct Value
Johannes K Knobloch1, Susanne Pfefferle2, Marc Lütgehetmann2
1Institute for Medical Microbiology, Virology and Hygiene, Department for Infection Prevention and Control, University Medical Center Hamburg-Eppendorf, Martinistr. 52, 20246 Hamburg, Germany.
Abstract:
SARS-CoV-2 RNA is frequently identified in patient rooms and it was speculated that the viral load quantified by PCR might correlate with infectivity of surfaces. To evaluate Ct values for the prediction of infectivity, we investigated contaminated surfaces and Ct-value changes after disinfection. Viral RNA was detected on 37 of 143 investigated surfaces of an ICU. However, virus isolation failed for surfaces with a high viral RNA load. Also, SARS-CoV-2 could not be cultivated from surfaces artificially contaminated with patient specimens. In order to evaluate the significance of Ct values more precisely, we used surrogate enveloped bacteriophage Φ6. A strong reduction in Φ6 was achieved by three different disinfection methods. Despite a strong reduction in viability almost no change in the Ct values was observed for UV-C and alcoholic surface disinfectant. Disinfection using ozone resulted in a lack of Φ6 recovery as well as a detectable shift in Ct values indicating strong degradation of the viral RNA. The observed lack of significant effects on the detectable viral RNA after effective disinfection suggest that quantitative PCR is not suitable for predicting the infectivity of SARS-CoV-2 on inanimate surfaces. Ct values should therefore not be considered as markers for infectivity in this context.
Insights
Quantitative PCR (qPCR) Ct values may not reliably indicate SARS-CoV-2 infectivity on surfaces. Effective disinfection reduced viable virus, yet Ct values remained unchanged, suggesting qPCR is unsuitable for predicting surface contamination risk.
Area of Science:
- Environmental Microbiology
- Infectious Diseases
- Molecular Diagnostics
Background:
- SARS-CoV-2 RNA detection on surfaces is common, raising questions about viral load and infectivity.
- Quantitative PCR (qPCR) is used to detect viral RNA, but its correlation with surface infectivity is unclear.
Purpose of the Study:
- To evaluate if Ct values from qPCR can predict the infectivity of SARS-CoV-2 on contaminated surfaces.
- To assess the impact of disinfection on viral RNA persistence and infectivity.
Main Methods:
- Investigated SARS-CoV-2 RNA on ICU surfaces and attempted virus isolation.
- Used surrogate bacteriophage Φ6 to test disinfection efficacy and Ct value changes.
- Applied UV-C, alcoholic disinfectant, and ozone for disinfection.
Main Results:
- SARS-CoV-2 RNA was found on 37/143 surfaces, but virus isolation failed, even from high-load surfaces.
- Disinfection reduced Φ6 viability significantly.
- UV-C and alcohol disinfection showed minimal change in Φ6 Ct values despite viability loss.
- Ozone disinfection degraded Φ6 RNA, causing detectable Ct value shifts.
Conclusions:
- Quantitative PCR Ct values are not suitable for predicting SARS-CoV-2 infectivity on inanimate surfaces.
- Ct values should not be used as markers for surface contamination infectivity in clinical settings.
