Transcript Document 7308056

Fate and Transport of Pathogens in
the Environment
Charles P. Gerba
Department of Soil, Water and
Environmental Science
The University of Arizona
Tucson, Arizona
How Important is the Environment
in Disease Transmission?
• 80% of all infections are acquired through
the environment
• Most other infections are acquired from
insect bites and direct personal contact (e.g.
sex, hand shaking, kissing)
Import Things to Remember about
Microbial Transport and Fate
• Microbes are colloids – not solutes
– Log-normal or Possion distributions
• Microbial transport is influenced by
electrostatic and hydrophobic interactions
• Microbes are individuals
Routes of Exposure
• Ingestion
– Water
– Food
– Hand to mouth (fomites)
• Inhalation (aerosols)
• Dermal
Factors Important in Assessing
Exposure
• Route of Exposure
• Duration of exposure
– Seconds, hours, minutes
• Number of exposures
– How many times in a day, month, year
• Degree of exposure
– Liters of water ingested
– Liters of air inhaled
– Grams of food ingested
Percentage of Estimated Foodborne
Illness Attributable by Agent*
Bacteria
30%
Viral
67%
*Mead et al., 1999
Protozoan 3%
Sources of Foodborne
Organisms
• Infected animal
• Cross contamination
– Cutting board to produce (vegetables)
• Irrigation water
• Handling and processing
– Hand to produce
– Wash water
– Ice
Transport and fate of enteric viruses in the marine environment
Aerosolization
by breaking waves
Sewage outfall
Virus association with suspended
solids (acts to prolong virus survival)
Resuspension by rain,
wave action, tides,
dredging, etc.
Accumulation in sediments
(viruses occur in higher concentrations
in sediment than the overlaying water)
Uptake by crustacea
and bottom feeding fish
FACTS
• 42 million people in the United States
depend on private wells for their source of
drinking water
• There are 100,000 small water treatment
systems in the U.S. (< 10,000 persons)
• 60 million persons depend upon septic tanks
for treatment of household wastes
Air/Water Interface
Viruses
Life in the
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•
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•
st
21
Century
Most of our time is spend indoors
More people work in offices than ever before
We travel more than ever before
We spend less time cleaning than the last
generation
• We are less clean (e.g. laundry practices)
• We spend more time in public places
• We are more mobile and have more electronic
equipment (e.g. cell phones)
Most Diseases Spread
Through Hand Contact
• Every three minutes, a child brings his/
her hand to nose or mouth
• Every 60 seconds, a working adult
touches as many as 30 objects
Occurrence of fecal bacteria on
the hand (United States)
Preparing a meal
Greatest
Children after playing
Doing the laundry
Person exiting a toilet
Least
Disease Spread by Fomites
• Route of exposure
– Children under 12 months to their face 60 times per
hour
– Cross contamination of foods
• Which fomites are important
– How often does hand contact occur on which fomites?
• Frequency of pathogens on fomites in a given
environment
• Concentration of pathogen on a fomite
Transmission by Fomites
• Hard surfaces
– Phones, tap handles, desk tops, door knobs,
cutting boards, table tops
• Cleaning clothes
– Sponges, dish clothes
• Clothing
– Laundry, towels, bed sheets
Transmission by Fomites
• Bathroom (Bano)
– Sinks, taps, bottom of the toilet seat
– Norovirus, Graidia, Cryptosporidium, Shigella
• Kitchen
– Sponge, sink, cutting board
– Salmonella, Campylobacter
• Schools
– Norovirus, rhinovirus, Salmonella
Geometric mean per cm 2 or per mL
Sites by Coliform Densities
7
6
5
4
3
2
1
0
-1
-2
Sponge Kitchen
Sink
Bath
Sink
Cutting
Board
Kitchen
Floor
Bath
Floor
Bath
Counter
Toilet
Seat
Classrooms (Grades 4-6)
• Areas most contaminated with bacteria
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Pencil sharpener
Student desk top
Computer
Sink in classroom
• Viruses isolated
– Influenza
– Norovirus
– Parainfluenza
% Time Coliform Bacteria
Detected (public restrooms)
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Top of the toilet seat
Flush handle
Wall behind toilet
Floor in front of toilet
Sink
Tap
20
6
9
64
61
15
% Time Coliform Bacteria
Detected (public restrooms)
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•
•
•
Urinal – inside
Urinal flush handle
Sanitary napkin disposal –outside
Door knob
30
0
57
4
MRSA Occurrence not Related to
Total Bacterial Numbers in Cars
Figure 3
Bacteria Numbers According to Site
HPC CFU/mL
Average
100000
10000
1000
100
Window
Opener
Seat
belt
Radio
Knob
Seat
Steering Change
Wheel holder
Car
Seat
Cup
Holder
Food
spills
Door
handle
Dash
board
Staph. aureus in Autos
Percent
Frequency of S. aureus Isolation According to Site
10
9
8
7
6
5
4
3
2
1
0
Seat
Change
holder
Door
handle
Food
spills
Radio
Knob
Car Seat Window
Opener
Dash
board
Cup
Holder
Seat belt Steering
Wheel
The Forgotten Fomites – Critical
Control Points?
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Phone (cell phone)
TV remote
Computer keyboard
Computer mouse
Sink taps/handles
Sponges/cleaning clothes
Laundry
Bio aerosols
Types of Bioaerosols
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•
•
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Sneezing
Showers
Cooling towers
Waste handling
– Sewage treatment
– Land application of biosolids and sewage
– Compost facilities
Factors Affecting the Survival of
Microorganisms in Aerosols
• Relative humidity ( Depends upon the
microorganism – optimal may be at either
high, low, or medium relative humidity)
• Sunlight (UV light) Longer survival at night
• Suspending media (lower survival in the
presence of organic matter
• Temperature – greater survival at lower
temperatures
Summary
• Temperature and sunlight (UV light) are the
major factors determining the survival of enteric
pathogens in the environment
• Viruses can travel long distances in groundwater
• Shellfish concentrate enteric bacteria and viruses
from water
• Enteric pathogens survive less in seawater than
freshwater