Difference between revisions of "Fomites"

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Fomites are any nonliving object such as books, desks, floors, clothing, paper, and phones that humans interact with and touch.  These fomites can be contaminated with pathogens, which survive and may accumulate on the surface and these pathogens can be spread microbes from person to fomite to person. Fomites are experienced and encountered everyday and are more frequently touched (eg per day) than other exposure routes, such as swimming, food (three meals) or drinking water (eg. 4 glasses of water). When developing a [[Quantitative Microbial Risk Assessment|QMRA]] around fomite exposures, there are a number of key pieces of information and data that need to be addressed. First how does the pathogen find its way to the fomite and what concentrations may be laid down on the fomite, second how well does the pathogen survival on fomites and finally how is the pathogen transferred from the fomite to the exposure individual.  [[CAMRA]] investigators have begun to address some of these data needs. Survival of pathogens on fomites are summarized as decay rates  ([[# Survival on the fomites|survival]]). 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|stochastic modeling]] (i.e. Markov chain models).   
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Fomites are any nonliving object such as books, desks, floors, clothing, paper, and phones that humans interact with and touch.  These fomites can be contaminated with pathogens, which survive and may accumulate on the surface and these pathogens can be spread microbes from person to fomite to person. Fomites are experienced and encountered everyday and are more frequently touched (eg per day) than other exposure routes, such as swimming, food (three meals) or drinking water (eg. 4 glasses of water). When developing a [[Quantitative Microbial Risk Assessment|QMRA]] around fomite exposures, there are a number of key pieces of information and data that need to be addressed. First how does the pathogen find its way to the fomite and what concentrations may be laid down on the fomite, second how well does the pathogen survival on fomites and finally how is the pathogen transferred from the fomite to the exposure individual.  [[CAMRA]] investigators have begun to address some of these data needs. Survival of pathogens on fomites are summarized as decay rates  ([[#Survival on the fomites|survival]]). 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|stochastic modeling]] (i.e. Markov chain models).   
 
   
 
   
 
Transfer efficiency is an area which is not well studied, and requires data on hand to fomite interactions and the % of microorganisms transferred to the hand or fingers and then the transfer of the microorganisms from the hand to the face, eye, mouth, and nose.     
 
Transfer efficiency is an area which is not well studied, and requires data on hand to fomite interactions and the % of microorganisms transferred to the hand or fingers and then the transfer of the microorganisms from the hand to the face, eye, mouth, and nose.     

Revision as of 15:07, 18 August 2011

Introduction

Fomites are any nonliving object such as books, desks, floors, clothing, paper, and phones that humans interact with and touch. These fomites can be contaminated with pathogens, which survive and may accumulate on the surface and these pathogens can be spread microbes from person to fomite to person. Fomites are experienced and encountered everyday and are more frequently touched (eg per day) than other exposure routes, such as swimming, food (three meals) or drinking water (eg. 4 glasses of water). When developing a QMRA around fomite exposures, there are a number of key pieces of information and data that need to be addressed. First how does the pathogen find its way to the fomite and what concentrations may be laid down on the fomite, second how well does the pathogen survival on fomites and finally how is the pathogen transferred from the fomite to the exposure individual. CAMRA investigators have begun to address some of these data needs. Survival of pathogens on fomites are summarized as decay rates (survival). 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).

Transfer efficiency is an area which is not well studied, and requires data on hand to fomite interactions and the % of microorganisms transferred to the hand or fingers and then the transfer of the microorganisms from the hand to the face, eye, mouth, and nose.


Transfer Efficiency

Transfer efficiency is made up of recovery, survival and percent that is transferred. The testing apparatus and method (i.e. swab or wipe with a broth) is used to evaluate the concentrations on the fomite and can be described as recovery. Transfer efficiencies from fomites to hands or fingers are specifically estimated based on the hosts touching 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, usually evaluate different fomite materials. The fomites are typically coated or otherwise inoculated with a known amount of pathogens and/or pathogen surrogates, then recovery can be addressed this can be performed through the use of swabs; transfer is evaluated via the touching of the contaminated fomite with human fingers or human finger surrogates. Table 1 shows the transfer efficiencies, reported as percent (%) of inoculated organisms recovered from the fomite via fingers.

Transfer Efficiency from Fomites to Hand

Table 1. Transfer 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 ratio of the numbers of remaining cultivatible cells (CFU, PFU, MPN units) which are viable divided by the starting concentration at any given time point with a rate of reduction over time obtained from the statistics of a best fit curve of several time points. First order decay rate is XXXX and is often described as a K value via log10 reduction/time (in hours or days).

The simple formula or concept is as follows for calculating k

M0 =microbe numbers at time zero, Mt = microbe numbers at time t, T is time t.

K.jpg


For example for a bacteria measured in CFU

K example.jpg


Experimental design for assessing survial varies greatly and are dependent on the date of publication (different techniques available in 1911 as compared to 2011). However the basic experimental plan is to have live pathogens exposed to air, in water, on surfaces and through monitoring and determine the remaining numbers at given time intervals. Thus addressing how much is 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. Recovery is presumed to be constant at time zero as well as over time, and therefore does not impact the calculated rates (this assumption may or may not be correct).


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)

Survival of Pathogens on Various Fomite Materials

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 25 100 0.13 Wilkinson (1966)
65 0.07
10 0.01
37 100 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)

Survival of Pathogens in Water, and Specific Types of Water (i.e. Stormwater)

Table 5: Survival Rate of Pathogens in Water
Pathogen Strain Media Notes Temperature (oC) Decay Rate (log10/hr) Source
Bacillus anthracis Not Reported Freeze Dried in Glass
Bottles
100 0.27 Dearmon et al. (1956, 1962)
90 0.07
80 0.01
Pasteur pH 7 Buffer 70 0.52 Mentville et al. (2005)
80 7.06
9- 69.80
Pasteur Milk 70 0.29
80 3.82
90 60.00
Pasteur pH 4.5 Buffer 70 6.52
80 31.60
90 70.60
Pasteur Orange Juice 70 6.45
80 20.00
90 88.20
Vollum pH 7 Buffer 70 0.26
80 2.01
90 12.20
Vollum Milk 70 0.30
80 2.47
90 8.96
Vollum pH 4.5 Buffer 70 0.60
80 7.50
90 37.50
Vollum Orange Juice 70 0.73
80 7.89
90 30.00
Francisella tularensis Not Reported Tap Water 8 3.9 (10-3) Forsman (2000)
Cell Culture Media 37 1.73 (10-2) Dearmon et al. (1962)
26 1.18 (10-2
15 1.03 (10-4
3 3.02 (10-4
0 4.79 (10-4
Freeze Dried in
Peptone Broth
37 6.16 (10-3
27 1.56 (10-3)
15 2.55 (10-3
3 3.82 (10-5
-18 1.77 (10-5
Vaccinia virus Not Reported Storm Water 4.5 1.40 (10-3) Essbaur et al. (2007)
19 - 23 1.39 (10-2)
Storm water with
Fetal Calf Serum
4.5 1.40 (10-3)
19 - 23 3.00 (10-3)
Storm Water and Soil 4.5 8.00 (10-3)
19 - 23 3.47 (10-2)
Tap Water 9 1.00 (10-3) - 2.80 (10-3) Mandell et al. (2005)
15 4.00 (10-4)
River Water 9 1.00 (10-3) - 3.40 (10-3)
15 1.00 (10-3) - 2.60(10-3)
Seawater 11.5 3.56 (10-3) Balawat et al. (1976)
Phosphate Buffer
Solution
3.13 (10-3)
Flaviviridae
(Hemorrhagic)
Yellow Fever
Virus
0.9% Saline 37 1.40 (102-) Adebayo et al. (1998)
Adenovirus
(Hemorrhagic)
Not Reported Seawater 6 2.82 (10-3) Balawat et al. (1976)
Phosphate Buffer
Solution
11.5 1.21 (10-2)
Bunyaviridae hantavirus
(Hemorrhagic)
Not Reported Cell Free Media 4 1.70 (10-3) Hardestam et al. (2007)
20 2.50 (10-2)
37 3.47 (10-2)
Not Reported 23 6.40 (10-3 Kallio et al. (2006)
4 1.20 (10-3)
23 6.50 (10-2)
4 2.60 (10-3)
Bunyaviridae hantavirus
(Hemorrhagic)
Not Reported Cell Free Media 4 1.00 (10-4) Hardestam et al. (2007)
20 2.60 (10-3)
37 1.19 (10-2)

References

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

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

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

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

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

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