It is necessary to facilitate sciencebased practice of environmental hygiene ( e . g ., standardization of hospital-wide cleaning and disinfection of noncritical environmental surfaces and medical devices per institutional policy ), not only in ordinary times but also in emergency times such as the current COVID-19 era .” medical equipment using disinfectants effective in inactivating SARS-CoV-2 . It is necessary to facilitate science-based practice of environmental hygiene ( e . g ., standardization of hospital-wide cleaning and disinfection of noncritical environmental surfaces and medical devices per institutional policy ), not only in ordinary times but also in emergency times such as the current COVID-19 era .”
As with many discussions around transmission of healthcare-associated infections , it is imperative to address the connection between fomites and hands .
Wilson , et al . ( 2020 ) used quantitative microbial risk assessment to relate log10 surface disinfection efficacy to COVID-19 infection risk . As the researchers note , “ Under low viral bioburden , minimal log10 reductions may be needed to reduce infection risks for a single hand-to-fomite touch to levels lower than 1:1,000,000 , as a risk-comparison point . For higher viral bioburden conditions , log10 reductions of more than 2 may be needed to achieve median infection risks of less than 1:1,000,000 .”
As the researchers acknowledge , “ While droplet and bioaerosol transmission are considered the main contributors to COVID-19 transmission , SARS-CoV-2 detection on surfaces indicates the potential for fomite-mediated transmission and the need for surface disinfection in multi-barrier mitigation approaches . Data indicate that surfaces most likely to facilitate coronavirus transmission are surfaces which are frequently touched by many people ( e . g ., door and tap handles ) and that disinfection practices should be targeted at these surfaces . Disinfectant efficacy on surfaces contaminated with coronavirus has been evaluated , but the log10 reductions obtained have not been quantitatively linked to infection risk reduction . This challenges health authorities in specifying disinfectant dilutions and contact times required to reduce viral bioburden to safety target levels , but risk assessment bridges the divide between environmental virus quantification and implementation of health targets .”
In their study , Wilson , et al . ( 2020 ) used a quantitative microbial risk assessment ( QMRA ) approach to estimate and compare COVID-19 infection risks after single hand-to-fomite-to-mucosal membrane contacts for high and low levels of viral bioburden and variable disinfection efficacy . They estimated infection risks for a single hand-to-fomite and hand-to-facial mucosal membrane ( mouth , eyes , and nose ) contact scenario , where reduction efficacy of the virus was varied between 1 and 5 log10 . The
researchers then compared estimated infection risks to 1:10,000 and 1:1,000,000 risks – an approach used in previous QMRAs for relating surface disinfection efficacies against bacteria and viruses to estimated health outcomes .
Wilson , et al . ( 2020 ) note that “ data are lacking describing infective virus bioburdens on fomites in part due to detection limits for current culture assays being higher than viral concentrations on surfaces . Therefore , we assumed a range of viral bioburden ( 0.1 to 10,000 genome copies ( gc )/ cm2 ) to evaluate the effect of variable viral bioburden on infection risk reductions offered by various log10 viral bioburden reductions and used 1 gc / cm2 , an assumed limit of detection , to compare low versus high viral bioburden conditions . To account for variations in the level of infectivity of viral genome copies , bioburdens were adjusted to assume either 1 % or 10 % of gc / cm2 were infective .”
The researchers found that under low viral bioburden conditions (< 1 genome copies ( gc )/ cm2 ), the average infection risks were below 1:1,000,000 , regardless of whether there was log10 reduction or whether 1 percent or 10 percent of the genome copies were assumed to be infectious . For the scenarios where there were high viral bioburdens ( 1-10,000 gc / cm2 ) and there was no log10 reduction in viral bioburden , few infection risks were below 1:1,000,000 regardless of whether 1 percent or 10 percent of genome copies / cm2 were infective , they report . Under these same high viral bioburden conditions , average infection risks were below 1:1,000,000 when viral bioburden was reduced by 1 to 5 log10 .
These simulations , according to the researchers , indicate that under low viral bioburden conditions , minimal log10 reductions may be needed to achieve risks less than 1:1,000,000 . For higher viral bioburden conditions , log10 reductions of more than 2 may be needed to achieve median risks of less than 1:1,000,000 , especially when assuming 10 percent of gc / cm2 represent infective virus .
The CDC recommends a 1000 ppm bleach dilution for non-porous surface disinfection , where appropriate . The model by Wilson , et al . ( 2020 ) demonstrates that a 2-3 log10 reduction would likely result in risks less than 1:1,000,000 for high-viral bioburden scenarios if 1 percent of gc / cm2 is assumed to be infective , according to the researchers ; however , this reduction range would be less adequate in achieving risks below 1:1,000,000 when a higher fraction of infective virus is expected . They