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Food- and Water-Borne Disease
Jonathan M. Links, PhD
Johns Hopkins University
Section A
Food-Borne Diseases
Food-Borne Diseases: Definitions
„
„
Food-borne diseases
− Those resulting from consumption of any solid food or
milk, water, or other beverage
Outbreak (CDC)
− Two or more persons experiencing a similar illness after
ingestion of a common food or beverage
− Epidemiologic analysis implicates the food/beverage as
the source of illness
Source: MMWR.
4
700
600
500
400
25000
300
200
10000
20000
15000
Cases
Cases
Outbreaks
Food-Borne Outbreaks: 1988–1997
5000
100
0
19
88
19
89
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
0
Outbreaks
Source: MMWR.
Cases
5
Total Burden of Food-Borne Illness
Illnesses
Hospitalizations
Deaths
76,000,000
323,000
5,200
Source: Mead, P. S. et al. (1999). Food-related illness and death in the United States. EID, 5, 607–625.
6
Causes of Food-Borne Outbreaks, 1988–1997
60
50
Percent
40
30
20
10
0
Unknown
Source: MMWR.
Bact.
Chem.
Viral
Parasitic
7
Number of Causative Organisms
„
Number of causative organisms involved in confirmed foodborne illnesses
Number of Causative Agents
40
30
20
10
0
1950
Source: MMWR.
1960
1970
1980
1990
2000
8
Extent of the Problem
OCCUR?
REPORTED
Food known, agent known, causes known
9
Food Safety Issues
Microbial
Contamination
Food
Additives
Natural
Toxins
Food
Pesticide
Residues
Environmental
Contaminants
10
Selected Infectious Agents and Their Main Habitats
Microorganism
Main habitat
Bacillus cereus,
Clostridium botulinum
Ubiquitous in soil and on vegetables
Campylobacter
Intestine of animals, fowl, and humans
E. coli, Salmonella
Lower intestine of humans, warmblooded animals, birds
Shigella
Intestine of humans and primates
Staphylococcus aureus
Common on human skin and oropharynx
Vibrio cholerae
Intestine of humans
11
Selected Infectious Agents and Their Main Habitats
Microorganism
Main habitat
Giardia lamblia
Intestine of humans, beavers, and
muskrats
Cryptosporidium
Intestine of humans and warm-blooded
animals
Trichinella spiralis
Striated muscle of carnivorous and
omnivorous animals
Hepatitis A virus
Intestine of humans
Norwalk virus
Intestine of humans
12
The Bacterial Growth Curve
9
8
c
Log10/ml
7
d
a: Lag
b: Exponential (logarithmic)
c: Stationary
d: Decline
6
5
b
4
3
2
a
0
4
8
12
16
20
24
28
32
Hours at 37oC
13
Minimal Infective Doses
„
Minimal infective doses for some pathogens and parasites
Organism
Minimal dose
Salmonella spp.
104–107
Shigella spp.
101–102
Escherichia coli
106–108
Escherichia coli O157:H7
~10
Vibrio cholerae
103
Giardia lamblia
101–102 cysts
Cryptosporidium
101 cysts
Hepatitis A virus
1–10 PFU
14
Multiplication of L. monocytogenes in Broth
Multiplication of L. monocytogenes in broth at low
temperature
8
4o C
7
6
Bacteria per ml
„
5
4
3
-20oC
2
1
0
0
1
6
3
Weeks of storage
12
15
Preferred Temperature Ranges for 4 Types of Bacteria
„
Relative growth rate of bacteria at different temperatures
Source: Doyle, M. P.
16
Extension of Shelf Life of Raw Foods by Cool Storage
Average useful storage life (days)
0oC (32oF)
22oC (72oF)
Meat
6–10
1
Fish
2–7
1
Poultry
5–18
1
Fruits
2–180
1–29
Leafy vegetables
3–20
1–7
90–300
7–50
Food
Root crops
17
Moisture Requirement
„
Water activity; aw
Water vapor pressure of food
Aw=
Water vapor pressure of pure water
„
„
„
Free water in food is necessary for microbial growth
Each microbial species has an optimum, maximum, and
minimum aw for growth
In general, a higher aw facilitates microbial growth
18
Water Activity of Various Foods
Food
Fresh fruit, vegetables, meat, fish
aw
>0.98
Cooked meat, bread
0.95–0.98
Cured meats, cheeses
0.91–0.95
Sausages, syrups
0.87–0.91
Rice, beans, peas
0.80–0.87
Jams, marmalades
0.75–0.80
Candies
0.65–0.75
Dried fruits
0.60–0.65
Dehydrated milk, spices
0.20–0.50
19
Lowest aw Values Permitting Growth of Microorganisms
Group of microorganisms
Minimal aw value
Many bacteria
0.91
Many yeasts
0.88
Many molds
0.80
Halophilic bacteria
0.75
Osmotic yeasts
0.60
20
Oxygen-Reduction (O-R) Potential
„
„
„
„
O2 tension or partial pressure of O2 about a food and the O-R
potential (the oxidizing and reducing power of the food)
influence the types of organisms that will grow in the food
Aerobes—Require free oxygen
− Most microorganisms
Anaerobes—Grow best in the absence of free oxygen
− Clostridium spp.
Facultative—Grow well either aerobically or anaerobically
− Enterobacteriaceae family
21
pH
22
Foods Associated with Foodborne Illness
Food vehicle
Microorganism
Beef and pork
Salmonella, S. aureus, E. coli, B. cereus, T. spiralis, L.
monocytogenes
Poultry
Salmonella, Campylobacter, S. aureus, L.
monocytogenes
Dairy products
Salmonella, Campylobacter, E. coli, L. monocytogenes,
Brucella
Eggs
Salmonella, S. aureus
Dried cereal
B. cereus and other Bacillus spp.
23
Foods Associated with Foodborne Illness
Food vehicle
Microorganism
Vegetables
C. botulinum, C. perfringence, Salmonella, Shigella, B.
cereus, Norwalk virus
Fish
C. botulinum, C. perfringence, ciguatera and scombroid
toxins
Shellfish
V. parahaemolyticus, V. cholerae, Hepatitis A, Norwalk
virus, neurotoxic and paralytic shellfish poisoning
Chinese food
B. cereus (in fried rice)
24
Some New Food Vehicles for Transmission
„
„
„
„
Internal content of eggs
− Salmonella enteritidis
Apple cider (low pH)
− E. coli O157:H7
Imported raspberries
− Cylospora
Oysters
− Norwalk-like virus
25
Changes in Host Susceptibility
„
„
„
Increase in diseases that cause immunosuppression
− AIDS 1988–1996: 22,000 to 223,000 cases
Increase in use of immunosuppressive agents
− Number of organ transplants
1988–1996: 12,000 to 22,000
Aging of the population
− Percentage of U.S. population >65 years old: 1950–1990:
8% to 15%
26
Host Factors and Susceptibility/Resistance to Infection
„
„
„
„
Personal hygiene
− Sanitary conditions; number of organisms ingested
Gastric acidity (pH ~ 3.4; acid barrier)
− 99.9% of ingested coliforms killed within 30 minutes
− Majority of pathogens never reach intestine
− Antacids increase susceptibility and severity of
gastrointestinal infections
Intestinal motility
− Fluid absorption processes
− Maintaining appropriate distribution of indigenous
enteric microflora
− Ridding host of pathogenic microorganisms
Specific immunity
27
Section B
Water-Borne Diseases
Global Total Water and Freshwater Reserves
Total water resources
Freshwater resources
Other
0.97%
Oceans
96.5%
Source: Pickering, K. T.
Freshwater
reserves 2.53%
Permafrost
0.97%
Rivers, lakes,
swamps
0.34%
Groundwater
29.9%
Glaciers and permanent
snow cover
68.7%
29
The Hydrologic Cycle
Source: Adapted by CTLT from Nadakavukaren, A.
30
Sources of Freshwater
„
„
„
„
Groundwater
− Available at point of need at little cost
− Until recently was not polluted
Surface water
− Usually requires extensive purification
Protected runoff
Ocean and brackish waters
− Costly to desalinate
31
Water System Facts
32
Freshwater Facts
„
„
Body composition
− Body, 65% water; blood, 83%; bones, 25%
− Water loss: 1% thirst; 5% hallucinations; 15% death
Basic requirements for safe water
− Drinking: 2–3 liters/day
− Minimum acceptable standard for living (WHO)
X 20–50 liters/capita/day for cooking and basic hygiene
33
600
600
500
500
400
400
300
300
200
200
100
100
1950
1960
Water consumption
Source: Gabler, R.
1970
1980
Daily withdrawal (billion gallons)
Total population (millions)
U.S. Water Consumption and Population Growth Rates
1990
Population
34
Distribution of U.S. Domestic Household Water Use
Use
Gallons/capita/day
Percent of total
Toilet flushing
23
40
Body washing
20
37
Drinking
3
5
Laundry
4
7
Dishwashing
4
7
Garden watering
3
5
Car washing
1
2
Total
58
100
All other*
1359
*Irrigation, livestock, commercial, industry, mining, etc.
Source: Tchobanoglous, G.
35
Current Water Issues
„
„
„
„
„
Vulnerability of surface water to:
− Drought (not replenished); i.e., lakes, reservoirs
− Diversion of rivers for agricultural and urban use
Declining groundwater levels
− Failure to replenish
− Compaction of aquifers
− Saltwater intrusion
Surface water pollution from nonpoint sources
Groundwater pollution
Increasing competition for water supplies
− World’s available freshwater is not distributed evenly
36
Sources of Groundwater Contamination
Source: Adapted by CTLT from Nadakavukaren, A.
37
Surface Water Contamination
„
Point and nonpoint sources of surface water contamination
Source: Adapted by CTLT from Bucholz, R. A.
38
Classes of Water Pollutants
Oxygen-demanding wastes
Plant and animal material
Infectious agents
Bacteria, viruses, protozoans
Plant nutrients
Fertilizers: nitrates, phosphates
Organic chemicals
Pesticides, detergents
Inorganic chemicals
Acids from coal mine drainage, inorganic
chemicals from steel plants
Sediment from land erosion
Clay silt on stream beds
Radioactive substances
Waste products from mining and
processing
Heat from industry
Cooling water used in steam generation of
electricity
Source: McKinney, M. L.
39
Major Causes of Stream and River Pollution
17% Municipal sources
Nonpoint
sources
65%
9% Industrial sources
6% Dredge and landfill
3% Unknown
Source: Wagner, T.
40
Water Purification
„
„
Goals
− Provides safe source of water that meets quality
objectives
− Reasonable cost
Sources
− Surface water
X Serves 52% of the U.S. population
− Groundwater
X Serves 48% of the U.S. population
Source: Patrick, R.
41
Typical Contaminants Found in Raw Water
„
Typical contaminants found in raw water that need to be
removed to meet specific water quality criteria
Class
Groundwater
Surface water
Bulky materials
None
Branches, leaves, algal mats,
soil particles
Colloidal materials
Microorganisms, trace
organic and inorganic
material
Clay, silt, organic materials,
pathogenic organisms, algae,
other microorganisms
Source: Tchobanoglous, G.
42
More Typical Contaminants Found in Raw Water
Class
Groundwater
Dissolved
materials
Fe, Mn, hardness ions, inorganic
salts, trace organic compounds
Dissolved gases
Carbon dioxide, hydrogen sulfide
Immiscible liquids
Source: Tchobanoglous, G.
Surface water
Organic compounds,
tannic acids, harness ions,
inorganic salts
Oils and greases
43
Simplified Flowchart of Drinking Water Treatment
DRINKING WATER SOURCE (RAW WATER)
COAGULATION, THEN FLOCCULATION
Chemical treatment to form floc,
which is allowed to settle from water
SEDIMENTATION
FILTRATION
To remove remaining solids
DISINFECTION
Chlorine to kill microorganisms
DISTRIBUTION SYSTEM
44
Water Disinfection Requirements
„
„
Must destroy bacteria, viruses, and amebic cysts in water
within a reasonable time despite all variations in water
temperature, composition, and concentration of
contaminants
Must not be toxic for humans and domestic animals,
unpalatable, or otherwise objectionable
45
Water Disinfection Requirements
„
„
„
Must be reasonable in cost and safe and easy to store,
transport, handle, and apply
Residual concentration in the treated water must be easily
and, preferably, automatically determinable
Must be sufficiently persistent so that the disappearance of
the residual would be a warning of contamination
46
Chlorine
Chlorine is the
favored disinfectant
for water supplies
Chlorine
kills microorganisms
Chlorine
reacts with
ammonia and
other
substances
Source: ReVelle, P.
Remaining
chlorine, termed
“free,” is available
to disinfect any
new input of
microorganisms
47
Inactivation Curves of Microorganisms
„
Inactivation curves of microorganisms following disinfection
100
Percent survival
A. Sensitive homogeneous population
B. More resistant homogeneous population
C. Heterogeneous population or one partially
protected by aggregation
A
B
C
0
Time
48
Microbial Inactivation by Chlorine
„
Microbial inactivation by chlorine (99.9% of organisms killed)
Chlorine concentration
(mg/L)
Inactivation time
(minutes)
Ct
(concentration x time)
0.5
1.0
0.5
1.0
0.5
0.5
2.0
0.25
0.5
The organism, temperature and pH are the same
49
Microbial Inactivation by Chlorine: Ct Values*
Chlorine
Conc., mg/L
Inactivation time
(minutes)
Ct
E. coli
0.1
0.4
0.04
Poliovirus
1.0
1.7
1.7
E. histolytica cysts
5.0
18
90
G. lamblia cysts
5.5
100
250
Microorganism
Cryptosporidium
>250
*99.9% kill; Temp. - 5oC; pH = 6.0
Source: Bitton, G.
50
The Shortcomings of Chlorine
„
Chlorine does not kill protozoan cysts and some resistant
viruses
Raw sewage
Treated sewage
Rivers
streams
Rivers
and&streams
Reservoirs
and&lakes
Reservoirs
lakes
Pristine surface water
Drinking water
0
Source: McFeters, G. A.
20
40
60
80
Percent of samples positive for oocysts
100
51
Chlorine Reaction Products
„
„
Chlorination has the potential of reacting with some organic
compounds present in the water supply to create
trihalomethanes (THM; chloroform)
Surface water supplies, high in dissolved natural organic
material (humics), are especially vulnerable to THM formation
52
Chlorine Reaction Products
„
„
When free chlorine is the disinfectant, THM levels are
generally higher in communities using rivers and streams as
their source of drinking water than in communities using
wells
THMs are potentially carcinogenic
53
Activities Permitted for Various Coliform Levels
„
Activities permitted for various levels of coliform bacteria in
water
Coliform level per
100 ml of water
Activity permitted
1 coliform or fewer
Water safe for drinking
4 coliforms or more
State must be notified and corrective
measures taken
2,300 coliforms or fewer
Swimming is allowed
10,000 coliforms or fewer
Boating is allowed
54
Section C
Wastewater
Wastewater Components of Concern
Wastewater components of concern
Pathogens
Nutrients
(N and P)
BOD*
Suspended
solids
Toxic
chemicals
*Biological oxygen demand (oxygen-demanding substances)
56
Some Primary Constituents of Municipal Sewage
Constituents
Potential sources
Effects in water
Oxygen-demanding
substances
Organic material
(human feces)
Consumes dissolved O2
Pathogens
Human waste
Cause disease
Nutrients
Detergents
Algal nutrients
Toxic chemicals
Industrial waste
Toxicity
Suspended solids
Silt
Interferes with
disinfection
57
Enteric Organisms in U.S. Surface Water and Sewage
„
Estimated levels of enteric organisms in U.S. sewage and
polluted surface water—concentration per 100 ml
Raw sewage
Polluted stream
water
Coliforms
109
105
Enteric viruses
102
1–10
Giardia
10
0.1–1
10–103
0.1–102
Organism
Cryptosporidium
Source: Pepper, I. L.
58
Biological Oxygen Demand (BOD5)
„
„
„
„
Organic decomposition requires oxygen
BOD is defined as the amount of oxygen used by organisms in
a body of water to carry out decomposition
The amount of oxygen utilized by microorganisms to oxidize
organic compounds in the dark at 20ºC in 5 days (BOD5)
CH2O + O2
H2O + CO2
bacteria
59
Biological Oxygen Demand (BOD5)
„
„
When bacteria act upon organic matter in sewage, large
amounts of dissolved oxygen are rapidly used up; this can
result in fish kills and drastic alterations of the aquatic
environment
BOD is an indication of how much putrecible organic material
is present in the water, with low BOD indicating good water
quality, and high BOD reflecting polluted conditions
60
BOD5 of Selected Waters
Water source
BOD5 (mg/L)
Domestic sewage
Raw
300
Treated
10
Textile dying
600
Dairy wastewater
900
Tannery wastewater
1,270
Slaughterhouse wastewater
2,000
Rubber factory
3,300
Distillery vinasse
Swine lagoon
30,000
800
Open feedlot runoff
1,000
Raw swine manure
50,000
61
Why Are Nitrates and Phosphates Pollutants?
„
„
„
Eutrophication
− Premature aging of an aquatic system
− Excessive nutrient level and subsequent excessive growth
of algae eventually fills up a lake and transforms it into a
marsh or a bog
Source
− Domestic sewage and animal sewage, fertilizer runoff,
detergent (P)
Effect on dinoflaggelates (Pfiesteria)
− Fishkills
62
Simplified Flowchart of Wastewater Treatment
Wastewater
Primary
Pretreatment
Physical methods to remove solid materials
Sedimentation
Suspended solids allowed to settle
Secondary
Grit
Primary
sludge
BIOLOGICAL TREATMENT
Uses microorganisms to digest soluble substances
SEDIMENTATION
Tertiary
Secondary
sludge
SPECIALIZED TREATMENT
Removes phosphorus and nitrogen
DISINFECTION
DISCHARGE OF EFFLUENTS TO RECEIVING STREAM
63
Municipal Sewage Treatment
„
The aim of sewage treatment is to improve the quality of
wastewater to the point that it can be discharged into a
waterway without seriously disrupting the aquatic
environment or causing human health problems in the form
of waterborne disease
64
Municipal Sewage Treatment
„
With few exceptions, water purification and wastewater
treatment processes are alike in concept and in kind
− They differ only in the amount of pollutants they must
remove and in the degree of purification they must
accomplish
65
Municipal Sewage Treatment: Primary Treatment
„
Primary treatment consists of simply holding sewage in a
large tank to permit the removal of solids by sedimentation
− Before entering the settling tank, the sewage is
commonly sent through a chamber or collector to
remove sand, grit, and small rocks that would otherwise
damage pumps or other equipment in the treatment
plant
66
Municipal Sewage Treatment: Secondary Treatment
„
Whereas primary treatment is based upon physical and
mechanical methods of removing suspended solids from
wastewater, secondary treatment depends on biological
processes—similar to naturally occurring decomposition, but
greatly accelerated—to digest organic waste
67
Municipal Sewage Treatment: Tertiary Treatment
„
Tertiary treatment, if done, removes nutrients such as
nitrogen and phosphorus
68
Municipal Sewage Treatment: Disinfection
„
Disinfection: Since most waterborne diseases are caused by
pathogenic bacteria, viruses, or protozoans present in human
excrement, one of the primary purposes of sewage treatment
is to kill such organisms before they can infect new victims
69
Municipal Sewage Treatment: Disinfection
„
Disinfection: Primary and secondary treatment leave a
substantial number of live organisms still remaining in the
wastewater
− Therefore, it has been standard procedure for many years
to disinfect treated effluent by adding chlorine prior to
discharge in order to eliminate any remaining diseasecausing organisms
70
Municipal Sewage Treatment: Chlorination
„
More recently, the policy of chlorinating all sewage treatment
plant discharges has met with increasing resistance and
today more than half of all states no longer require
chlorination of wastewater
71
Municipal Sewage Treatment: Chlorination
„
There are several reasons for this change in accepted practice
− Chlorine is effective in killing bacteria but less so in
relation to protozoans and viruses
− Chloramines are formed which may be toxic to aquatic
life
− Chlorine treatment is expensive
72
Viruses and
protozoans
Pathogenic
bacteria
Nitrogen
Phosphorus
Dissolved
organics
Sewage
solids
Removal of Contaminants by Sewage Treatment
Primary
treatment
Secondary
treatment
Tertiary
treatment
Disinfection
Source: ReVelle, P.
Still
detectable
73
Average annual number of
waterborne disease outbreaks
Waterborne Outbreaks (U.S.)
40
30
20
10
1938– 1941– 1946– 1951– 1956– 1961– 1966– 1971– 1976– 1980–
1940 1945 1950 1955 1960 1965 1970 1975 1980 1985
Source: Gabler, R.
74
Outbreaks by Public Water System Deficiencies
„
Percentage distribution of waterborne disease outbreaks
caused by deficiencies in public water systems
Distribution
network problems
21%
Miscellaneous
9%
Inadequate
or interrupted
treatment
27%
Contaminated
untreated surface water
8%
Contaminated
untreated groundwater
35%
Source: Bitton, G.
75
Agents Associated with Cases of Waterborne Diseases
„
Etiologic agents associated with cases of waterborne diseases
Bacterial
10%
Giardia
11%
Acute gastrointestinal illness of
unknown origin (AGI)
43%
Viral AGI
15%
Source: Pepper, I. L.
Cryptosporidium
20%
76
Classification of Water-Related Illnesses
„
Classification of water-related illnesses associated with
microorganisms
Class
Cause
Examples
Waterborne
(fecal-oral)
Pathogens that originate in fecal
material and are transmitted by
ingestion
Cholerae, giardiasis,
salmomellosis, poliomyelitis,
typhoid, E. coli
Watershed
Pathogens that originate in feces
and are transmitted through
contact because of inadequate
sanitation or hygiene
Infectious eye and skin diseases,
louse-borne typhus and
relapsing fever
Water-based
Organisms that originate in water
or spend part of their life cycle in
water and come in direct contact
with humans in water
Schistosomiasis, dracunculiasis
(helminths)
Water-related insect vector
Microorganisms with life cycles
associated with insects that live or
breed in water
Malaria, yellow fever, dengue
fever, filariasis
77
Key Points
„
„
„
„
The hydrological cycle controls the availability of freshwater,
which is diminishing
Groundwater and surface water are polluted by both point
and nonpoint sources
Water purification is used to provide potable water; chlorine
is the favored disinfectant
Wastewater treatment must address pathogens, suspended
solids, toxins, nitrogen and phosphorus, and BOD
78
Key Points
„
„
„
„
„
Microbial contamination represents the greatest food hazards
The extent and magnitude of foodborne disease outbreaks
are largely underestimated
Microbial growth in food depends on nutrient availability,
moisture content, redox potential, temperature, and pH
Host susceptibility factors are an important determinant in
foodborne diseases
Food preservation is used to prolong shelf life
79