Fate%20and%20Transport%20of%20Pathogens%20in%20the%20Environment

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Fate and Transport of Pathogens in the Environment
Charles P. Gerba Department of Soil, Water and
Environmental Science The University of
Arizona Tucson, Arizona
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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)

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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

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Routes of Exposure

• Ingestion
• Water
• Food
• Hand to mouth (fomites)
• Inhalation (aerosols)
• Dermal

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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

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Percentage of Estimated Foodborne Illness
Attributable by Agent
Bacteria 30
Viral 67
Protozoan 3
Mead et al., 1999
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Sources of Foodborne Organisms

• Infected animal
• Cross contamination
• Cutting board to produce (vegetables)
• Irrigation water
• Handling and processing
• Hand to produce
• Wash water
• Ice

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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
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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. (lt 10,000 persons)
• 60 million persons depend upon septic tanks for
  treatment of household wastes

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Viruses
Air/Water Interface
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Life in the 21st 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)

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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

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Occurrence of fecal bacteria on the hand (United
States)

• Preparing a meal Greatest
• Children after playing
• Doing the laundry Least
• Person exiting a toilet

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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

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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

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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

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Sites by Coliform Densities
Bath Sink
Cutting Board
Kitchen Sink
Sponge
Bath Floor
Kitchen Floor
Bath Counter
Toilet Seat
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Classrooms (Grades 4-6)

• Areas most contaminated with bacteria
• Pencil sharpener
• Student desk top
• Computer
• Sink in classroom
• Viruses isolated
• Influenza
• Norovirus
• Parainfluenza

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Time Coliform Bacteria Detected (public
restrooms)

• Top of the toilet seat 20
• Flush handle 6
• Wall behind toilet 9
• Floor in front of toilet 64
• Sink 61
• Tap 15

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Time Coliform Bacteria Detected (public
restrooms)

• Urinal inside 30
• Urinal flush handle 0
• Sanitary napkin disposal outside 57
• Door knob 4

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MRSA Occurrence not Related to Total Bacterial
Numbers in Cars
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Staph. aureus in Autos
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The Forgotten Fomites Critical Control Points?

• Phone (cell phone)
• TV remote
• Computer keyboard
• Computer mouse
• Sink taps/handles
• Sponges/cleaning clothes
• Laundry

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Bio aerosols
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Types of Bioaerosols

• Sneezing
• Showers
• Cooling towers
• Waste handling
• Sewage treatment
• Land application of biosolids and sewage
• Compost facilities

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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

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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