Fomites

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Introduction

Fomites are any nonliving surface that can harbor a pathogen. Fomites are experienced and encountered everyday and are typically more commonly encountered than other exposure routes, such as drinking water. When developing a QMRA for fomites, there are a number of key pieces of information and data that need to be addressed. First the pathogen survival on fomites must be addressed, this available data that has been used in past QMRAs by CAMRA and non CAMRA investigators. Survival of pathogens on fomites are summarized as decay rates of the pathogens, according to it's natural life cycle on the particular fomites. Decay rates are given as first order loss rates since they are defined simply as a loss of pathogen viability over time, this also works well for stochastic modeling (i.e. Markov chain models), as first order loss rates are used. Also the decay rate while simple in


Transfer Efficiency

Transfer efficiency can be defined differently based on the scenario being considered. In the case of testing the contamination level of a room, the transfer efficiency from fomite surface (i.e. table top) to the testing apparatus (i.e. swab), this gives a sampling transfer efficiency. Transfer efficiencies from fomites to hands or fingers are specifically for the development of a risk estimate based on the hosts touching those contaminated fomites. In either case transfer efficiencies are unitless parameters, as they describe the percentage of pathogens contaminating a fomite, that transfer to the fingers or hands.

Transfer efficiency experiments, test the relative ability of different fomite materials. The fomites are typically coated or otherwise inoculated with a known amount of pathogens and pathogen surrogates, then recovery is attempted, this can be performed through the use of swabs, human fingers or human finger surrogates. Table 1 shows the recovery efficiencies, reported as percent (%) of inoculated organisms recovered from the fomite. Table 2 is specific to a human finger contacting the fomites tested. Tests were performed by Gerardo Lopez PhD. Candidate working with CAMRA under the advisement of Dr. Charles P. Gerba with the University of Arizona.


Transfer Efficiency from Fomites to Hand

Table 1. Recovery Efficiencies from both porous and non-Porous Fomites
Porous and Non-Porous Fomites
Pathogen Relative Humidity Acrylic Ceramic Tile Cotton Glass Laminate Paper Money Polyester Stainless Steel
Bacillus thuringiensis
17% - 30%
  Min = 45.8
Max = 74.8
μ = 57.0
σ = 12
N = 6
Min = 0.09
Max = 0.31
μ = 0.15
σ = 0.08
N = 6
Min = 0.52
Max = 0.78
μ = 0.63
σ = 0.11
N = 6
Min = 0.32
Max = 0.91
μ = 0.54
σ = 0.25
N = 6
Min = 0.05
Max = 0.2
μ = 0.13
σ = 0.05
N = 6
Min = 0.02
Max = 0.17
μ = 0.06
σ = 0.06
N = 6
Min = 0.15
Max = 1.7
μ = 0.63
σ = 0.57
N = 6
Min = 0.39
Max = 1.0
μ = 0.52
σ = 0.24
N = 6
40% - 65%
  Min = 48.8
Max = 84.9
μ = 65.6
σ = 15.9
N = 6
Min = 1.3
Max = 76.4
μ = 21.2
σ = 28.2
N = 6
Min = 0.85
Max = 10
μ = 3.5
σ = 3.5
N = 6
Min = 4.3
Max = 65.9
μ = 33.8
σ = 24.0
N = 6
Min = 33.8
Max = 79.0
μ = 53.5
σ = 19.6
N = 6
Min = 0.01
Max = 0.07
μ = 0.04
σ = 0.02
N = 6
Min = 0.61
Max = 1.63
μ = 1.2
σ = 0.38
N = 5
Min = 47.5
Max = 71.4
μ = 57.0
σ = 9.7
N = 6
E. coli O15597
17% - 30%
  Min = 1.1
Max = 93.5
μ = 49.5
σ = 44.5
N = 6
Min = 0.1
Max = 5.2
μ = 12.5
σ = 2.19
N = 6
Min = 3.4
Max = 50
μ = 16.8
σ = 16.8
N = 6
Min = 0.7
Max = 15.1
μ = 5.4
σ = 5.6
N = 6
Min = 5.2
Max = 66.5
μ = 21.7
σ = 23.9
N = 6
Min = 0.017
Max = 0.12
μ = 0.046
σ = 0.04
N = 6
Min = 0.07
Max = 0.87
μ = 0.37
σ = 0.28
N = 6
Min = 1.5
Max = 100
μ = 19.6
σ = 39.5
N = 6
40% - 65%
  Min = 29
Max = 100
μ = 66.1
σ = 31.4
N = 6
Min = 3.28
Max = 100
μ = 71.9
σ = 37.5
N = 6
Min = 10
Max = 50
μ = 27.7
σ = 15.1
N = 6
Min = 0.25
Max = 100
μ = 58.5
σ = 38.2
N = 6
Min = 1.9
Max = 46.4
μ = 14.8
σ = 17.2
N = 6
Min = 0.065
Max = 0.65
μ = 0.14
σ = 0.25
N = 6
Min = 0.06
Max = 2.2
μ = 0.69
σ = 0.78
N = 6
Min = 48.9
Max = 98.9
μ = 68.6
σ = 21.4
N = 6
MS-2 bacteriophage
17% - 30%
  Min = 3.0
Max = 40.6
μ = 21.7
σ = 15
N = 6
Min = 3.78
Max = 15
μ = 7.10
σ = 4.03
N = 6
Min = 0.01
Max = 0.05
μ = 0.03
σ = 0.02
N = 6
Min = 2.90
Max = 40.5
μ = 19.3
σ = 13.2
N = 6
Min = 1
Max = 10
μ = 5.35
σ = 3.56
N = 6
Min = 0.13
Max = 0.95
μ = 0.42
σ = 0.38
N = 6
Min = 0.05
Max = 0.70
μ = 0.26
σ = 0.25
N = 5
Min = 4
Max = 40
μ = 13.7
σ = 13.5
N = 6
40% - 65%
  Min = 35.2
Max = 100
μ = 67.9
σ = 27.2
N = 6
Min = 16.8
Max = 74.7
μ = 33.4
σ = 22.5
N = 6
Min = 0.04
Max = 0.64
μ = 0.26
σ = 0.26
N = 6
Min = 37.4
Max = 96.9
μ = 67.3
σ = 25
N = 6
Min = 2.79
Max = 95.7
μ = 53.3
σ = 33.4
N = 6
Min = 0.09
Max = 1.45
μ = 0.66
σ = 0.53
N = 6
Min = 1.19
Max = 3.20
μ = 2.26
σ = 0.081
N = 5
Min = 19.5
Max = 62.4
μ = 37.4
σ = 16
N = 6
Staphylococcus aureus
17% - 30%
  Min = 0.36
Max = 3.1
μ = 1.5
σ = 1.1
N = 6
Min = 0.80
Max = 6.7
μ = 2.7
σ = 2.3
N = 6
Min = 0.44
Max = 1.9
μ = 0.96
σ = 0.60
N = 6
Min = 0.6
Max = 85.4
μ = 20.3
σ = 33.4
N = 6
Min = 1.3
Max = 7.4
μ = 4.2
σ = 2.4
N = 6
Min = 0.09
Max = 0.44
μ = 0.23
σ = 0.14
N = 6
Min = 0.04
Max = 0.13
μ = 0.37
σ = 0.48
N = 6
Min = 1.13
Max = 11.9
μ = 3.9
σ = 3.9
N = 6
40% - 65%
  Min = 24.4
Max = 67.3
μ = 47.2
σ = 17.9
N = 6
Min = 27.7
Max = 77.6
μ = 54.7
σ = 18.8
N = 6
Min = 0.07
Max = 1.32
μ = 0.50
σ = 0.46
N = 6
Min = 25.7
Max = 65.5
μ = 45.5
σ = 15.5
N = 6
Min = 30.9
Max = 89.9
μ = 61.9
σ = 24.7
N = 6
Min = 0.06
Max = 0.32
μ = 0.18
σ = 0.10
N = 6
Min = 0.07
Max = 15.46
μ = 5.04
σ = 6.86
N = 6
Min = 16.6
Max = 85.5
μ = 48.3
σ = 25.4
N = 6

Transfer Efficiencies from Hand-to-Mouth

Table 3. Transfer Efficiencies from Hand-to-Mouth for Humans, Summarized from Rusin et al. (2002)
Microorganisms
Number of Subjects Transfer Efficiency *
Micrococcus luteus
20
0.41
PRD-1 bacteriophage
0.34
Serratia rubidea
0.34
*: Defined as -- CFU on lip/sum(CFU on lip, CFU recovered from transfer finger)

Rusin, P. Maxwell, S., Gerba, C. (2002) Comparitive Surface-to-Hand and Fingertip-to-Mouth Transfer Efficiency of Gram-Positive Bacteria, Gram-Negative Bacteria, and Phage Journal of Applied Microbiology 93 585-592 [Full Text via Google Scholar

Contact rates

Table 4: The numbers of hand contacts with the eyes, lips and nostrils observed during a continuous 3-hour period for ten subjects
Subject Eyes Lips Nostrils Total
1 0 0 3 3
2 4 2 1 7
3 2 12 4 18
4 1 1 20 22
5 10 22 15 47
6 13 33 8 54
7 17 15 27 59
8 6 31 28 65
9 9 52 30 91
10 12 72 20 104
Mean 7.4 24 16 47
Mean Rate (hr-1) 2.47 8.0 5.33 15.7
Standard Deviation 5.7 24 11 35
Standard Deviation Rate (hr-1) 1.9 8.0 3.7 11.7

(Mark Nicas, University of California Berkeley)

Survival on the fomites

Survival is typically defined as a first order decay rate. Experimental design varies dependent on the time of the paper (different techniques available in 1911 as compared to 2011). However the basic experimental plan is to have live pathogens exposed to air and through monitoring and testing determine the time with which a set number (i.e. 50% for half life) inactivated in the matrix of interest (e.g air, water etc.). For decay rates on fomites, the chosen fomite(s) is(are) inoculated with a known amount of pathogens and then the survival of these pathogens are monitored again recording how the total number is degrading over time.

Survival of Pathogens on Fomites and Environmental Matrices

Table 4. Survival Rates of Pathogens in Aerosols (Air)
Aerosols
Pathogen Strain or Surrogate Temperature (oC) Relative Humidity (%) Decay Rate (log10/hr) Source
Bacillus anthracis Not Reported Not Reported Not Reported 4.64 (10-7) Stuart et al. (2005)
Francisella tularensis Schu S5 -40 Ambient 0.97 Erlich and Miller (1995)
-29 Ambient 0.25
-7 Ambient 0.37
24 85 0.55
29 85 0.90
35 85 2.08
Live Vaccine Strain 90 Not Reported 0.03 Cox (1971)
Cox and Goldberg (1972)
80 Not Reported 1.20
70 Not Reported 2.09
60 Not Reported 8.00
50 Not Reported 9.59
40 Not Reported 9.39
30 Not Reported 9.20
20 Not Reported 3.97
0 Not Reported 3.95
Live Vaccine Strain
freexe dried in peptone broth
90 Not Reported 6.15 Cox (1971)
Cox and Goldberg (1972)
80 Not Reported 9.20
70 Not Reported 7.83
60 Not Reported 6.71
50 Not Reported 6.09
40 Not Reported 4.18
30 Not Reported 4.00
20 Not Reported 1.31
0 Not Reported 1.20
Yersinia pestis A-1122 26 87 3.49 Won and Ross (1966)
50 2.10
20 2.66
Variola major Vaccinia virus 10.5 - 11.5 20 0.00 Harper (1961)
10.5 - 11.6 50 0.00
10.5 - 11.7 80 0.02
21.0 - 23.0 20 0.03
21.0 - 23.1 50 0.03
21.0 - 23.2 80 0.13
31.0 - 33.5 20 0.03
31.0 - 33.6 50 0.11
Vaccinia virus McLlvaine buffer
1% horse serum
22 20 0.01 Harper (1963)
10 50 0.05
10 80 0.09
Arenaviridae
(Hemorrhagic Fever)
Venezuelan equine
encephalitis virus
9.0 - 9.5 19 0.00 Harper (1961)
48 0.02
86 0.05
21 - 23 19 - 23 0.04
50 0.10
81 - 86 0.12
20.5 - 23.5 19 0.09
48 0.22
81 - 85 0.86
Arenaviridae
(Hemorrhagic Fever)
Lassa virus Josiah strain 24 30 1.12 Stephenson et al. (1984)
55 1.08
80 1.41
32 30 0.68
55 0.60
80 0.55
38 30 0.59
Flaviviridae
(Hemorrhagic Fever)
Japanese encephalitis
virus Peking strain
24 30 0.17 Larsen et al. (1980)
55 0.24
80 0.33
Flaviviridae
(Hemorrhagic Fever)
St. Louis encephalitis
Parton strain
Not Reported 80 0.13 Rabey et al. (1969)
80 0.16
60 0.08
61 0.20
46 0.07
46 0.09
35 0.03
23 0.001
Flaviviridae
(Hemorrhagic Fever)
Marburg virus Not Reported Not Reported 3.00 Belanov et al. (1966)
Table 4. Survival Rates of Pathogens on Fomites
Pathogen Strain Fomite Material Temperature (oC) Relative Humidity (%) Decay Rate (log10/hr) Source
Francisella tularensis Live Vaccine Strain Metal 100 0.13 Wilkinson (1966)
65 0.07
10 0.01
100 0.46
80 0.38
65 0.37
55 0.25
Yersinia pestis A1122 Metal 11 30 0.04 Wilkinson (1966)
100 30 0.20
52 30 16.90
52 22 0.69
Stainless Steel 18 - 22 55 0.98 Wilkinson (1966)
Polyurithane 0.21
Glass 1.13
Paper 0.07
Harbin Stainless Steel 18 - 22 55 1.24 Rose et al. (2003)
0.91
Polyurithane 0.85
0.25
Glass 0.06
0.06
Paper 0.07
0.04
Variola major Variola minor Scabs in Envelopes 15 - 30 35 - 98 2.79 (10-3) Wolf et al. (1968)
Vaccinia virus Glass Slides 25 96 6.43 (10-3) Mahl and Sadler (1975)
55 9.95 (10-3)
7 6.41 (10-3)
37 93 5.45 (10-3)
55 6.87(10-3
3 6.25 (10-3)

Exposure models

References

Busson B (1911) Ein Beitrag zur Kenntnis der Lebensdauer von Bacterium coli und Milzbrandsporen. 58.

Mitscherlich E, Marth EH (1984) Microbial survival in the environment: bacteria and rickettsiae important in human and animal health. Springer-Verlag. Berlin, Germany Book Details and Abstract

Graham-Smith GS (1930) The longevity of dry spores of B. anthracis. Journal of Hygiene 30 213-215. Full Text via NIH.gov

Novel R, Reh. T (1947) De la longevite des spores du Bacillus anthracis et de la conservation des pouvoirs pathogene et antigene. Pathobiology formerly Schweizerische Zeitschrift für allgemeine Pathologie und Bakteriologie 10 180-192.

Szekely AV (1903) Beitrag zur Lebensdauer der Milzbrandsporen. Hyg Infectionskrankh 44 359-363. Full Text via Google Scholar

Won WD, Ross H (1966) Effect of diluent and relative humidity on apparent viability of airborne pasteurella pestis. Applied and Environmental Microbiology 14 742-745. Full Text via NIH.gov

Rose LJ, Donlan R, Banerjee SN, Arduino MJ (2003) Survival of Yersinia pestis on environmental surfaces. Applied and Environmental Microbiology 69 2166-2171. Full Text via NIH.gov

Wilkinson Tr (1966) Survival of Bacteria on Metal Surfaces. Applied Microbiology 14 303-307. Full Text via NIH.gov

Cox CS, Goldberg LJ (1972) Aerosol Survival of Pasteurella tularensis and Influence OF Relative Humidity. Applied Microbiology 23 1-3. Full Text via NIH.gov

Cox CS (1971) Aerosol Survival of Pasteurella tularensis Disseminated From Wet and dry States Applied Microbiology 21 482-486. Full Text via NIH.gov

Ehrlich R, Miller S (1973) Survival of Airborne Pasteurella tularensis at Different Atmospheric Temperatures Applied Microbiology 25 369-372. Full Text via NIH.gov

Harper GJ (1961) Airborne Microorganisms - Survival Tests With 4 Viruses. Journal of Hygiene 59 479-486. Full Text via NIH.gov

Harper GJ (1963) The influence of environment on the survival of airborne virus particles in the laboratory. Arch Gesamte Virusforsch 13 64-71. Abstract

Mahl MC, Sadler C (1975) Virus Survival on Inanimate Surfaces Canadian Journal of Microbiology 21 819-823. Abstract

Stephenson EH, Larson EW, Dominik JW (1984) Effect of environmental factors on aerosol-induced lassa virus infection. Journal of Medical Virology 14 295-303. Abstract

Hardestam J, Simon M, Hedlund KO, Vaheri A, Klingstom J, et al. (2007) Ex vivo stability of the rodent-borne hantaan virus in comparison to that of arthropod-borne members of the Bunyaviridae family. Applied and Environmental Microbiology 73 2547-2551. Full Text via NIH.gov