Persistence of SARS-CoV-2 and its surrogate, bacteriophage Phi6, on surfaces and in water

The COVID-19 pandemic spurred research on the persistence of infectious SARS-CoV-2 and its surrogates, including bacteriophage Phi6, in environmental reservoirs. Despite the wide use of Phi6, side-by-side comparisons between Phi6 and SARS-CoV-2 are limited. Here, we quantified the persistence of SARS-CoV-2 and Phi6 on surfaces (PVC plastic and stainless steel), using an initial inoculum of 10(3) plaque forming unit per surface, and evaluated the influence of four commonly used deposition solutions on viral persistence. In addition, we quantified the persistence of SARS-CoV-2 and Phi6 in water. Our findings revealed that Phi6 had a significantly longer half-life than SARS-CoV-2 in water and on surfaces. Phi6 persisted 34 hours in water compared with 13 hours for SARS-CoV-2. Viral persistence on surfaces was significantly influenced by the virus used and the deposition solution but not by the surface material. Phi6 remained infectious significantly longer than SARS-CoV-2 when the inoculation solution was culture media and saliva, leading to half-lives between 9 hours and 2 weeks for Phi6, compared to 0.5–2 hours for SARS-CoV-2. Using phosphate-buffered saline as a deposition solution led to half-lives shorter than 4 hours for both viruses on all surfaces. Our results indicate that bacteriophage Phi6 may lead to an overestimate of infectiousness for studies quantifying SARS-CoV-2 persistence on surfaces and water and highlight the importance of using appropriate deposition solutions when evaluating viral persistence on surfaces. IMPORTANCE: The COVID-19 pandemic spurred research on the persistence of SARS-CoV-2 and its surrogates. Here we highlight the importance of evaluating viral surrogates and experimental methodologies when studying pathogen survival in the environment.