Support for Recommendations of Precleaning Before Disinfection: Limited Efficacy of Soapy Water as a Disinfectant against SARS-CoV-2

The World Health Organization (WHO) and US Centers for Disease Control and Prevention (CDC) recommend cleaning soiled surfaces with soap and water, followed by use of approved disinfectant. However, data are lacking on the potential efficacy of soapy water alone as a disinfectant for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is relevant to low-resource settings where soapy water is prevalent for handwashing. To our knowledge, no appropriate biosafety level 1 (BSL-1) surrogate has been identified and confirmed for use in studies with soapy water and the highly infectious SARS-CoV-2. Therefore, our objectives were to determine the efficacy of soapy water alone as a disinfectant against SARS-CoV-2 and if commonly used BSL-1 bacteriophage surrogates could serve as a surrogate model for testing soapy water as a disinfectant. Overall, results indicate that SARS-CoV-2 can be reduced $>4{\log }_{10}$ in suspension but only $0.50{\log }_{10}$ on a nonporous surface with 10 min of exposure to 0.5% soapy water. This difference is potentially attributed to less area of exposure on surfaces than in suspension. Phi6 (a verified SARS-CoV-2 surrogate for other disinfectants) was not appropriate for SARS-CoV-2 disinfection with soapy water. Further research is needed to determine an appropriate surrogate for SARS-CoV-2 disinfection with soapy water as disinfection of MS2 was similar to SARS-CoV-2 on surfaces only. Our work highlights the importance of confirming surrogates for each disinfectant used. Based on our results, we do not recommend a change to the current WHO and CDC surface disinfection protocols that recommend using soapy water to preclean a surface before applying disinfectant.