Transfer Efficiency of Bacteria and Viruses from Porous and Nonporous Fomites to Fingers under Different Relative Humidity Conditions

Abstract

Fomites can serve as routes of transmission for both enteric and respiratory pathogens. The present study examined the effect of low and high relative humidity on fomite-to-finger transfer efficiency of five model organisms from several common inanimate surfaces (fomites). Nine fomites representing porous and nonporous surfaces of different compositions were studied. Escherichia coli, Staphylococcus aureus, Bacillus thuringiensis, MS2 coliphage, and poliovirus 1 were placed on fomites in 10-l drops and allowed to dry for 30 min under low (15% to 32%) or high (40% to 65%) relative humidity. Fomite-to-finger transfers were performed using 1.0 kg/cm 2 of pressure for 10 s. Transfer efficiencies were greater under high relative humidity for both porous and nonporous surfaces. Most organisms on average had greater transfer efficiencies under high relative humidity than under low relative humidity. Nonporous surfaces had a greater transfer efficiency (up to 57%) than porous surfaces (<6.8%) under low relative humidity, as well as under high relative humidity (nonporous, up to 79.5%; porous, <13.4%). Transfer efficiency also varied with fomite material and organism type. The data generated can be used in quantitative microbial risk assessment models to assess the risk of infection from fomite-transmitted human pathogens and the relative levels of exposure to different types of fomites and microorganisms. I nanimate objects, or fomites, are a potential reservoir in the transmission of pathogens either directly, by surface-to-mouth contact, or indirectly, by contamination of fingers and subsequent hand-to-mouth, hand-to-eye, or hand-to-nose contact (1-5). Bodily fluids such as saliva, mucus, nasal secretions, blood, urine, and feces may all potentially contain pathogens that can be transmitted via fomites (6-9). A number of studies have shown that enteric and respiratory pathogens are capable of surviving from hours to months on fomites, depending on the numbers deposited, the type of microorganism, and the variable environmental conditions (10-12). Several studies have shown that inanimate surfaces found in day care centers (8,(13)(14)(15)(16)(17), schools (18), office buildings (19), homes (20-27), public areas (28), or hospitals (12, 29-33) can be reservoirs for secondary modes of transmission, with contaminated hands playing a critical role as a route of exposure.The efficiency of transfer of a pathogen to the hand from the fomite is important in modeling the potential for its transmission (11,(34)(35)(36). This information can be used to understand the spread of disease in indoor environments and the potential for designing surfaces that reduce transfer efficiency and/or are antimicrobial (5). The purpose of this work was to better elucidate the transfer efficiencies of several different types of organisms under control conditions to provide data that may be used in quantitative microbial risk assessment (QMRA) models. (ii) Gram-negative and Gram-positive bacterial inoculum preparation. Frozen aliquots of E. coli an...

Evaluation of a Disinfectant Wipe Intervention on Fomite-to-Finger Microbial Transfer

“…The information obtained in the present study can be used to model the probability of infection in disinfectant-wipe-treated and nontreated scenarios and assess microbial exposure via fomites. However, the lack of standard methods for quantifying microbial transfer makes it difficult to compare the results of different studies (43). In the present study, we used the same experimental parameters as in our previous study (43), such as the humidity level, fomite-to-finger contact pressure, drying time, sampling method, etc., which allowed us to compare the fomite-to-finger microbial transfer values from both studies.…”

“…However, the lack of standard methods for quantifying microbial transfer makes it difficult to compare the results of different studies (43). In the present study, we used the same experimental parameters as in our previous study (43), such as the humidity level, fomite-to-finger contact pressure, drying time, sampling method, etc., which allowed us to compare the fomite-to-finger microbial transfer values from both studies. In order to directly compare the transferred microbial numbers relative to the original microbial numbers on the fomite between treated and nontreated conditions, we used the "resulting transfer" defined by equation 1.…”

“…These microorganisms have been widely used as models of Gram-positive and -negative bacteria, spore-forming bacteria, and enteric viruses. Especially E. coli and S. aureus have been used in transfer studies (43,(54)(55)(56).…”

“…We conducted these experiments under clean-fomite conditions in order to minimize the variability of fomite surface conditions, which reflect the same experimental conditions as our previous study (43), but a previous study was conducted showing the efficacy of disinfectant wipes under dirty-and clean-surface conditions and reported a similar mean log 10 removal (30). However, an earlier study suggests that the presence of a higher organic material on surfaces can reduce the ability of the wipes to remove bacteria (29).…”

“…Recently, we reported fomite-to-finger transfer efficiencies of various types of microbial pathogens and fomites at different relative humidity levels (43). In the present study, we assessed the impact of a disinfectant wipe intervention on microbial transfer from contaminated fomites to fingers.…”