Figure 1.
Compartments and transmission routes.
The upper part of the figure models the flow of individual compartments. The transfer rate from susceptible (S) to infected (I) is the product of the pathogen amount on hands of susceptible (EHS), the fraction of pathogens EHS transferred to mucus of susceptible via inoculation (ρinoc) and the probability that a susceptible individual becomes infectious per pathogen. The recover rate of infected is γ per unit time. The lower part of the figure models the flow of pathogens. α is the shedding rate per unit time per individual. φH proportion of virus goes directly to the hands of an infected individual. The proportion of virus that is excreted to hands and then is associated with a type of fomite is ξ. λ is the fraction of pathogens going to surfaces reach one type of fomite. ρF is the individual pick up rate of pathogens on a fomite per unit time and δ is the deposit rate of pathogens from hands to fomites per unit time. µH and µF are virus inactivation rate on hands and fomites respectively.
Table 1.
Parameter Values Used in Comparison of R0s.
Table 2.
Fomites Classification Parameters and Derived Parameter Values.
Figure 2.
Total transmission potential and the percentage of transmission through hand-contaminated-fomite route.
A) total transmission potential (Reproduction number); B) the percentage of transmission through hand-contaminated-fomite route (R0_hF/R0F) as functions of the proportion of virus that settle on fomites (λ) and the personal touching rate (ρptr). Stars in the figures are the cases when the parameters take on values in Tables 1 and 2. Changes in ρptr have more impact on the fomite transmission when ρptr is low than when ρptr is high.
Figure 3.
Transmission potentials (Reproduction number).
A) Reproduction number for the hand-contaminated route (R0_hF) as functions of the fraction of virus shed on hands; B) reproduction number for the droplet-contaminated fomites route (R0_dF) as functions of the fraction of virus shed on hands. Note that scale for graph A) is one order of magnitude smaller than graph B). Values are shown for all fomites combined and individual fomite types. The upper limit of x-axis (0.5) is based on the assumption that the fraction shed to hands is less than that shed into air. The parameters for each of the four fomite classes graphed are presented in Tables 1 and 2. Stars in A and B are R0s of the two fomite routes when φH = 0.145.
Figure 4.
The total fomite transmission potentials.
Total fomite transmission potential (Reproduction number) as a function of A) shedding amount α/γ, B) dose response of virus on mucosa πF, C) fraction of virus shed on hands φH, D) inoculation rate ρinoc, E) virus inactivation rate on hands µH, F) virus inactivation rate on fomites µF, G) population size N, H) fraction of pathogen transferred from surface to hands ρtfsh, and I) fraction of pathogen transferred from hands to surface ρtfhs, stratefied by fomite types. Stars on the lines are values of R0_F when the parameters take on values in Tables 1 and 2. Across all variation considered, the highly touched large surface fomite type has the highest transmission potential. The slope of each line, which can be interpreted as strength of each hypothetical control, is largest for the highly touched large surface fomite type.
Figure 5.
The proportion of all transmission mediated through the hand-contaminated-fomite route.
The proportion of all transmission mediated through the hand-contaminated-fomite route as a function of A) fraction of virus shed on hands φH, B) virus inactivation rate on hands µH, C) fraction of pathogen transferred from hands to surface ρtfhs and D) inoculation rate ρinoc, stratified by fomite type. Stars on the lines are values of R0_F when the parameters take on values in Tables 1 and 2. The percentage of hand-contaminated-fomite route does not exceed 50% except when the fraction shed to hand is larger than 42% or when the virus inactivation rate on hands is less than 0.2/min or when the virus transfer fraction from hand to surface is larger than 48%.