Case Study Presentation by
Dr. T. G. Rupa
Ms. Kamayani Barshilia
Mr. Harshit Mishra
QMRA Summer School-2014
Mentors:
Prof. Marquez
Prof. Arun Kumar
Objective:
To assess microbial risks to
residents of village “DD”
using the water for drinking,
swimming and irrigation
activities.
Village BB
Waste water
discharge
Animal droppings
Village DD
5 km downstream
Stream AA
Drinking water
Stream “AA” is
discharging polluted
water (sewage & surface
runoff) into the Yamuna
river.
Field irrigation
Recreational bathing
Yamuna river
QMRA Summer School-2014
Steps for Microbial Risk
Assessment
Hazard Identification
Dose Response
Assessment
Exposure Assessment
Risk Characterization
Risk Management
QMRA Summer School-2014
(Source: Adopted from Penningroth, 2010)
Assumptions
1. The river has capability of natural treatment of
waste water.
2. The ratio of indicator organism to pathogen
organism remains constant.
3. Only three pathogens present in wastewater are:
•Salmonella sp.
•Shigella sp
•Vibrio cholerae
4. Survival of ingested pathogens is cent percent.
5. Only Oral pathway has been considered.
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Data Requirement
QMRA Steps
Parameter to be considered
Hazard Identification
Selection of pathogens, Ratio of indicator
organism to pathogen organism, Microbial
concentration
Exposure Assessment
Exposure pathway, Type of population
(Adults, Children), Water intake, Exposure
frequency, Exposure duration
Dose Response
Assessment
Dose response model
Risk Characterization
Calculation of risk (Point estimation, MonteCarlo Simulation), Sensitivity Analysis
QMRA Summer School-2014
Salmonella sp
 Rod-shaped, gram-negative, non-spore forming, predominantly






motile enterobacteria
Lives in animal and human intestines and are shed through
feces.
Infection occurs through through contaminated water or food.
Some common species - Salmonella Anatum and Salmonella
Meleagridis.
Causes gastroenteritis. Possible signs and symptoms include
nausea, vomiting, abdominal cramps, diarrhea, fever, chills,
headache, blood in the stool
Incubation period is 12 to 72 hours.
Vulnerable groups - The elderly, infants and those with impaired
immune systems
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Vibrio cholerae
 Comma shaped, gram-negative bacillus
 Occurs in both marine and freshwater habitats associated with







algal blooms (plankton) and aquatic animals
It is endemic or epidemic in areas with poor sanitation.
Infection through fecal-oral transmission by food or water
supply; multiply within the intestines
Incubation period is 24 to 48 hours
Symptoms - diarrhoea, dehydration, hypovolemic shock/death,
abdominal cramping, nausea, vomiting, fever and chills
Vulnerable groups – Children and pregnant women
Mortality <1% if treated with rehydration therapy. The disease
typically lasts from 4–6 days.
Not communicable
QMRA Summer School-2014
Shigella sp.
 Rod-shaped, gram-negative bacteria
 Transmission route is fecal-oral; bacteria is present in the stools of infected
persons while they are sick and for up to a week or two afterwards
 Infection spreads through poor hand hygiene, ingestion of contaminated
food or water, inadequate sanitation and toileting, overcrowding, contact
with a contaminated inanimate object, vectors like the housefly. 80% of all
infection is the result of person-to-person transmission.
 Common symptoms – diarrhea, fever, nausea, vomiting, stomach cramps,
and flatulence, large and painful bowel movements. The stool may contain
blood, mucus or pus.
 Incubation period varies from 12 hours to 7 days but is typically 2-4 days.
 Mortality rate <1% in developed countries; 20-25% in the east and middle
east.
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Concentration Of Pathogens
 fecal coliforms=1.5*107±8*102 MPN/100 mL (given)
Concentration MPN/100ml
Source: Pant, Anju & Mittal, Atul K. (2007). Monitoring of Pathogenicity of
Effluents from the UASB based Sewage Treatment Plant
QMRA Summer School-2014
Salmonella:
3.21E+02±1.71E-02
Shigella:
8.24E+01±0.004395604
Vibrio:
5.12E+02±2.73E-02
Exposure Assessment
SCENARIOS:
I. Drinking water (without treatment)
II. Bathing recreational activities 2 times/week (May-Aug)
III. Irrigation for spinach and cucumber crops
Exposure pathways
Drinking
Drinking
Swimming
Swimming
Routes of
exposure
Exposed sub
groups
Daily intake
Oral
Oral
Oral
Adults
Children
Adults
3L/day
1L/day
210ml
350
350
32
Children
(70ml/hr*3 hrs)
360ml
32
350
Oral
Exposure frequency
(days/year)
Consumption
Oral
Consumers
(120ml/hr*3hrs)
80ga
of cucumber
Consumption
Oral
Consumers
80g
3
of spinach
Farmers working
Oral
Farmers
50mg/day
365/2b
in the fields
Children playing
Oral
Children
100mg/day
365/2
in the fields
Source: Modified from Exposure factors handbook: 2011 edition, U.S. Environmental Protection Agency Washington, DC.
a. Gerba.C.P., Risk Assessment. b. Mara, D.D. Quantifying health risks in wastewater irrigation
QMRA Summer School-2014
Response Model Parameters for
selected pathogens
Agent strain
Best fit
model
Optimized
parameters
Salmonella
anatum
βPoisson
Salmonella
meleagridis
Salmonella
Typhi
Shigella
flexneri
Vibrio
cholerae
LD50/ID50
Route
Dose
units
α=3.18E-01,
N50=3.71E+04
3.71E+04 human oral, with
eggnog
inferred
MPN/ml
βPoisson
βPoisson
βPoisson
α=3.89E-01 ,
N50=1.68E+04
α=1.75E-01,
N50=1.11E+06
α= 2.65E-01,
N50=1.48E+03
1.68E+04 human oral, with
eggnog
1.11E+06
oral
1.48E+03 human oral(in
milk)
inferred
MPN/ml
inferred
MPN/ml
inferred
MPN/ml
βPoisson
α= 2.50E-01,
N50=2.43E+02
2.43E+02 human oral (with
NaHCO3)
inferred
MPN/ml
QMRA Summer School-2014
Host
endpoint
positive
stool
culture
infection
disease
positive
stool
isolation
infection
Risk
Calculation
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Daily and Annual risk of infection from Salmonella
pathogen (maximum Concentration)
CHILDREN
ADULT
Salmonella Shigella
Daily
infection
risk
Vibrio
Salmonella
Shigella
Vibrio
0.407
0.56
0.819
0.22
0.42
0.76
1
1
1
1
1
1
Tolreable Risk
1/10000
1/10000
1/10000
1/10000
1/10000
1/1000
0
Risk
reduction (%)
99.97
99.98
99.98
99.95
99.97
99.98
96.87
99.99
-
-
-
Annual
infection
risk
Reduction
117
99.99
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Risk of
Infection
Salmonella Shigella
(Drinking
Water)-Adults
P(Max)
0.407
0.56
P(Mean)
0.407
0.56
P(Min)
0.407
0.56
Risk of Infection
(Drinking
Salmonella Shigella
Water)-Children
P(Max)
0.227
0.424
P(Mean)
0.227
0.424
P(Min)
0.227
0.424
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Vibrio
0.819
0.819
0.819
Vibrio
0.763
0.763
0.763
Risk of Infection
(Recreational
Salmonella Shigella Vibrio
Activities)-Adults
P(Max)
P(Mean)
P(Min)
0.3313
0.3313
0.3312
0.5081 0.7985
0.5081 0.7985
0.5081 0.7985
Risk of Infection
(Recreational
Salmonella Shigella
Activities)-Children
P(Max)
0.222
0.4193
P(Mean)
0.222
0.4193
P(Min)
0.222
0.4193
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Vibrio
0.7605
0.7605
0.7605
Risk of
Infection (For Salmonella
spinach)-Adults
P(Max)
0.331
P(Mean)
0.331
P(Min)
0.331
Shigella
Vibrio
0.508
0.508
0.508
0.798
0.798
0.798
Risk of Infection
(For spinach)- Salmonella Shigella
Children
P(Max)
0.222
0.419
P(Mean)
0.222
0.419
P(Min)
0.222
0.419
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Vibrio
0.76
0.76
0.76
Risk of
Infection (For
Salmonella Shigella
Cucumber)Adults
P(Max)
0.939
0.913
P(Mean)
0.939
0.913
P(Min)
0.939
0.913
Risk of Infection
(For Cucumber)- Salmonella Shigella
Children
P(Max)
0.707
0.743
P(Mean)
0.707
0.743
P(Min)
0.707
0.743
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Vibrio
0.961
0.961
0.961
Vibrio
0.892
0.892
0.892
Monte-Carlo
Simulation for
Salmonella infection
QMRA Summer School-2014
Drinking water
QMRA Summer School-2014
Bathing recreational
activities
Risk Management
 Maximum allowable annual
risk
-4
of microbial infection : 10 per
year (USEPA)
 Risk communication and
reduction at two levels:
Village BB
 Mobilizing people to adopt waste
reduction techniques: Training
local leaders to disseminate
information and monitor the
progress
 Waste control/reduction at village
BB through 2-pit latrines, sulabh
shauchalayas, biogas plants
 Installing water treatment plant
Yamuna
Village DD
 Mobilize people to adopt healthful practices – e.g., boil drinking
water, wash hands properly, wash spinach and cucumber well
before consumption
 Protective gears for farmers
 Chlorination of water
 Training health workers from local population to disseminate
information on healthful practices, distribution of chlorine
tablets, detect any disease (water related) and recommend severe
cases to hospital
 Follow up
 Cost-effect analysis of using different strategies for risk
reduction and using the most suitable method
REFERENCES
Gerba, C.P. (1999). Risk Assessment. 212-219. Retrieved from
web.iitd.ac.in/~arunku/files/CEL899.../Gerba%20Risk%20Assessment.pdf.
Singh, D. and Kumar, A. Virus Pollution of Indian Surface Water: Health Risk Estimation and
Issues Identification. Retrieved from
https://piazza.com/drexel/summer2014/iheraii_delhiindia/resources.
Mara, D.D. (2008). Quantifying health risks in wastewater irrigation. In: UNESCO Encyclopedia
of Life Support Systems. EOLSS Publishers , Oxford.
Morris, Robert D. and Levin, R. 1995. Estimating the incidence of waterborne infectious
disease related to drinking water in the United States in Assessing and Managing Health Risks from
Drinking Water Contamination: Approaches and Applications (Proceedings of the Rome
Symposium, September 1994). IAHS Publ. no. 233, 1995. 75.
NCEA (2011). Exposure Factors Handbook. (2011 Ed.). EPA/600/R-09/052F. U.S.
Environmental Protection Agency Washington, DC.
Pant, Anju & Mittal, Atul K. (2007). Monitoring of Pathogenicity of Effluents from the UASB
based Sewage Treatment Plant in Environment Monitoring Assessment, 133:43–51.
Thank
You 
QMRA Summer School-2014