Hand disinfection substantially reduces relative risks of transmission independently of the disease ’ s prevalence and the frequency of contact , even with low ( 25 percent of people ) or moderate ( 50 percent of people ) compliance .
In contrast , the effectiveness of surface disinfection is highly dependent on the prevalence and the frequency of contacts .” emphasize that , “ More data are needed describing the relationship between molecularly detected virus and infectious virus concentrations , as this affects infection risk estimates and required log10 reductions needed to protect health at specific risk-informed levels . While 1:1,000,000 was used as a conservative point of comparison for estimated risks , this is a de minimis risk level . Improvements to risk comparisons in future work include comparing infection risks estimates to rates of increased number of illness cases . To better inform scenario-specific targeted surface hygiene , data are needed for SARS-CoV-2 bioburden on different environment-specific ( home or healthcare ) fomites and fomite-specific touch frequencies .”
What about fomite transmission of SARS-CoV-2 outside of the healthcare environment ?
Pitol and Julian ( 2020 ) used a QMRA framework to examine the risks of community transmission of SARS-CoV-2 through contaminated surfaces and to evaluate the effectiveness of hand and surface disinfection as potential interventions , with an outcome the researchers say “ supports the current perception that contaminated surfaces are not a primary mode of transmission of SARS-CoV-2 and affirms the benefits of making hand disinfectants widely available .”
The researchers say that the risks posed by contacting surfaces in communities are low , with community infection prevalence rates ranging from 0.2 percent to 5 percent and add that , “ Hand disinfection substantially reduces relative risks of transmission independently of the disease ’ s prevalence and the frequency of contact , even with low ( 25 percent of people ) or moderate ( 50 percent of people ) compliance . In contrast , the effectiveness of surface disinfection is highly dependent on the prevalence and the frequency of contacts .”
They do not acknowledge , however , that “ Indirect transmission via fomites ( contaminated surfaces ) contributes to the spread of common respiratory pathogens and evidence-to-date suggests fomite transmission is possible for SARS-CoV-2 . People infected with SARS-CoV-2 shed the virus into the environment , as evidenced by extensive SARS-CoV-2 RNA detected on surfaces in cruise ships , hospitals , and public spaces in urban areas such as bus stations and public squares . Infective coronavirus persists in the environment , with experimental evidence of persistence on surfaces ranging from three hours to 28 days , depending on environmental factors such as surface material and temperature . Viruses readily transfer from contaminated surfaces to the hand upon contact and from hands to the mucous membranes on the face . People touch their faces frequently , with studies reporting average hand-to-face contacts ranging from 16 to 37 times an hour . Taken together , this suggests surface contamination could pose a risk for indirect SARS-CoV-2 transmission , similar to other respiratory viruses .”
In their study , Pitol and Julian ( 2020 ) developed a model to estimate the risk of infection for single contacts with contaminated surfaces , with the concentrations of SARS-CoV-2 RNA on the surfaces informed by literature investigating surface contamination in public spaces ( bus stations , gas stations , stores , playgrounds ), while a second model was used to estimate risks from surface-mediated community transmission as a function of the prevalence of COVID-19 cases in the community and to test the efficacy of feasible intervention strategies of hand disinfection and surface disinfection .
As the researchers explain , “ The frequency of surface contamination was determined by the prevalence of the disease in the population . A cough was assumed to spread particles conically , so , virus inoculation on hands was modeled as a function of the concentration of virus in the saliva , the volume of saliva expelled per cough , the distance between the mouth and the hand , and the right circular cone angle of the ejected particles . Transfer from surfaceto-hand and from hand-to-mucous membranes was assumed proportional to the concentration of virus on the surface and the transfer efficiency of virus at both interfaces .”
The concentration on the contaminated surface and on the hand was reduced according to the log10 reduction values for the scenarios of surface and hand disinfection . Alcohol-based hand sanitizer was selected as hand disinfection strategy , and although handwashing was not considered , based on the log reductions of enveloped viruses achieved by handwashing , the researchers assumed that effectiveness of handwashing is similar to hand sanitizer for the reduction of SARS-CoV-2 on hands . The models were simulated 50,000 times , with the risks were calculated across time for seven days .
Studies have demonstrated that the average risk of infection from interaction with a contaminated fomite is linearly related to surface contamination , ranging from 2 × 10−8 for a surface with 0.01 RNA genome copies ( gc ) cm-2 to approximately 1 for a surface with ≥106 RNA gc cm-2 . Previous studies of surface contamination on public spaces have detected 0.1 to 102 SARS-CoV-2 gc cm-2 . In the two studies , only 3 of 1281 ( 0.2 percent ) surfaces sampled were associated with risks of infection greater than 1 in 10,000 . The average risk of infection for the sampled surfaces was of 8.5 × 10−7 , assuming negligible risks for samples with SARS-CoV-2 RNA below the LOD ( 1203 out of 1281 surfaces ). Two contact frequencies and three prevalence levels ( percentage of the population sick at any given time ) were modeled : high contact frequency [ 1-20 min ] and low contact frequency [ 60-240 min ] and low [ 0.2 percent ], medium [ 1 percent ], and high [ 5 percent ] prevalence . The risk of infection of 10-6 is equivalent to one person sick as a result of hand-to-mouth contact every million people touching the surface .
The researchers found that hand hygiene was consistently the most effective intervention : “ Even with low compliance , representative of only 1 in 4 people