Importantly , the impact of hand hygiene also appears to be independent of surface contact frequency and prevalence rates , suggesting a strategy of hand disinfection promotion in community settings is universally applicable .
disinfecting hands after surface contact , median infection risks from fomite contact were reduced by 0.6-2.2 log10 . Under high compliance , representing 3 of every 4 people disinfecting , median risks decreased by 3.8-4.3 log10 . Importantly , the impact of hand hygiene also appears to be independent of surface contact frequency and prevalence rates , suggesting a strategy of hand disinfection promotion in community settings is universally applicable . Our findings re-affirm the existing strategies of promoting hand hygiene and making hand disinfect products widely available in shared community settings .”
The researchers conclude that , “ Although the risks of SARS-CoV-2 transmission via fomites are estimated to be low , they are possible and may contribute a small number of new cases during outbreaks . For both surfaces with quantified contamination and modeled surfaces within a community , infection risk estimates are very low when people interact with a single fomite . However , a person ’ s infection risk increases when accounting for the hundreds of objects contacted every hour , and the thousands of frequently contacted objects ( crosswalk buttons , public transportation buttons , ATMs , and railings ) within a city . Each interaction provides an opportunity for SARS-CoV-2 transmission . Risk of infection from multiple contacts with fomites – as compared to a single contact with a fomite – is substantially higher . Nevertheless , in our models the risk of infection from a fomite is orders of magnitude lower than the prevalence rates , suggesting the relative contribution of fomite-mediated transmission might be small compared to other transmission routes .”
And how does SARS-CoV-2 fomite contamination compare with other pathogens of importance ?
Kraay , et al . ( 2018 ) analyzed fomite-mediated transmission across multiple pathogens ( influenza , rhinovirus , and norovirus ) and venues . The researchers developed and analyzed a model that accounts for fomite transmission by including pathogen transfer between hands and surfaces in two sub-types of fomite-mediated transmission : direct fomite ( e . g ., shedding onto fomites ) and hand-fomite ( e . g ., shedding onto hands and then contacting fomites ).
As the researchers explain , “ Based on parameter estimates from the literature the reproductive number ( R0 ) for the fomite route for rhinovirus and norovirus is greater than 1 in nearly all venues considered , suggesting that this route can sustain transmission . For influenza , on the other hand , R0 for the fomite route is smaller suggesting many conditions in which the pathway may not sustain transmission . Additionally , the direct fomite route is more relevant than the hand-fomite route for influenza and rhinovirus , compared to norovirus . The relative importance of the hand-fomite vs . direct fomite route for norovirus is strongly dependent on the fraction of pathogens initially shed to hands . Sensitivity analysis stresses the need for accurate measurements of environmental inactivation rates ,
• transfer efficiencies , and pathogen shedding .” They add , “ Fomite-mediated transmission is an important pathway for the three pathogens examined . The effectiveness of environmental interventions differs significantly both by pathogen and venue . While fomite-based interventions may be able to lower R0 for fomites below 1 and interrupt transmission , rhinovirus and norovirus are so infectious ( R0 >> 1 ) that single environmental interventions are unlikely to interrupt fomite transmission for these pathogens .”
Kraay , et al . ( 2018 ) note that hand contamination is separate from infection status – a person who is infected may not have contaminated hands and a susceptible person may have contaminated hands , explaining that , “ Individuals with contaminated hands may become infected through self-inoculation .” The dynamics of inoculum are driven by numerous factors , including method of inoculation and its probability of infection ; fomite-touching rates ; excretion ( shedding ) by an infectious individual at a rate that contributes to contamination of surfaces and hands ; pathogen inactivation ( decay ); recovery of individuals ; and cleaning and decontamination interventions .
Also coming into play are pathogen transmission venues , which Kraay , et al . ( 2018 ) describe as “ complex environments characterized both by their physical properties ( types and quantity of fomites ) and by the nature of host behaviors within these spaces ( frequency of contact with fomites , the duration of time spent in a venue , or the density of hosts within the venue ). Furthermore , risk within a venue may also vary by age group based on not only differences in contact rates but also shedding rates .”
Finally , surface composition and control measures also impact transmission parameters , such as the cleaning rate and the proportion of pathogens killed by decontamination . As the researchers say , “ For all pathogens , the inactivation rates on fomites were highly variable by surface , with higher inactivation rates on hands ( which are a porous surface ). Influenza had much higher inactivation rates on porous surfaces . Notably , some pathogens exhibited biphasic inactivation , with faster initial inactivation followed by a period of slow inactivation or persistence without measurable decay … While inactivation rates on fomites were relatively insensitive to temperature , they were more sensitive to changes in humidity , with drier conditions generally promoting higher inactivation rates . The exception was influenza , which appeared to survive better at low humidity .”
The researchers did note differences pertaining to transfer efficiencies among the pathogens they studied : “ For influenza and norovirus , transfer efficacies appear to be asymmetrical . Influenza transfers more readily from fomites to hands than hands to fomites . The reverse appears to be true for norovirus . However , studies of rhinovirus do not appear to measure directional transfer . For influenza , transfer efficiency was also lower for porous than non-porous surfaces ”.