4.
Problem Statement: To
assess the risk due to
the microorganisms that
the rag pickers are
exposed to.
Motivation: To
determine if it is
possible to formally
legalize the rag picking
business without
Legend:
Dumping sites 1, 2, 3, 4 are near to the residential district
Dumping sites 5, 6 and 7 are located further away
Dumping site 8 is a control site (construction waste)
Assume 1 million population in this city, with 1% of
4
population being rag pickers
5.
Goals of this QMRA
ā¢
ā¢
ā¢
ā¢
What is the magnitude of health risks faced by
rag pickers?
Which pathogen(s) pose the greatest risks to
rag pickers?
How does risk vary across dumping sites?
What interventions would be most
appropriate for:
1.
Mitigating health risks faced by rag pickers?
2.
5
Minimizing secondary transmission?
12.
Data Provided
ā¢
Dump Sites:
ā
ā
Bacteria and fungi (CFU/g)
ā
ā¢
Approximate location
Probability of transmission to rag pickers
Rag Pickers:
ā
Microorganism observation frequency by site
ā
Microorganism observation frequency by sample
type (stool/urine/nasal swab/sputum)
ā
Blood/Immune/Liver function
12
13.
Data ļ Exposure
Bacteria & Fungi isolated from different dump sites and control sites, CFU/g
1
2
3
4
5
6
7

1.2 x 106

1.1 x 106


0.1
1.2 x 106
1.2 x 106
1.4 x 106
1.1 x 106
1.4 x 106
1.2 x 106
1.1 x 106



1.1 x 106


0.2 x 106


1.9 x 106
1.3 x 106
1.1 x 106
1.2 x 106

1.4 x 106
1.1 x 106
1.2 x 106
1.2 x 106

BACTERIA/FUNGI
Candida sp.
Escherichia coli
Klebisiella sp.
Salmonella sp.
Staphylococcus aureus
2.1 x 106
1.4 x 106
1.4 x 106
1.2 x 106
8
Exposure factors from USEPA
Activities (adult male, 2131 yrs)
Soil and dust ingestion
Hand to eyelipnostril contact
50
15.7
Units
mg/day
times/h
Dermal exposure  adherence of soil to face
0.024
mg/cm2/d
Dermal exposure  adherence of soil to arms
0.0379
mg/cm2/d
Dermal exposure  adherence of soil to hands 0.1595
mg/cm2/d
Dermal exposure  adherence of soil to legs
0.0189
mg/cm2/d
Dermal exposure  adherence of soil to feet
Working week
Working hours
0.1393
6
6
mg/cm2/d
d/wk
h/d
BACTERIA
/FUNGI
Candida sp.
Escherichia coli
Klebsiella sp.
Salmonella sp.
P (transmission to rag picker
from dump site)
0.002
0.004
0.002
0.001
Staphylococcus aureus
13
0.001
14.
Data ļ Exposure
1. Ingestion dosage
Ingestion through mouth
contact
Klebsiella sp. conc in
MSW
Hands to mouth
1.1 x 106
15.7
P(transmission)
K. pneumoniae
Total per dose
0.002
0.1
4330.18
Accidental ingestion of
soil
CFU/g
times/h
Klebsiella sp. conc in
MSW
Soil and dust ingestion
Fraction
CFU
P(transmission)
K. pneumoniae
Total per dose
1.1 x 106
50
CFU/g
mg/day
0.002
0.1
11
Fraction
CFU
2. Subcutaneous dosage
Subcutaneous exposure
Klebsiella sp. conc in
MSW
Exposure
1100
0.3796
P(transmission)
K. pneumoniae
0.002
0.1
Subcutaneous dose
CFU/mg
mg/cm2
Fraction
0.83512
CFU/ cm2
14
Sum
4341.176 CFU/d
16.
Analysis Steps
1.
Evaluate data availability
2.
Identify availability of dose response curves
3.
Select āplannedā model
ā
Exponential or Ī²Poisson
4.
Estimate dermal and ingestion exposure
5.
Estimate k for Klebsiella sp. and Candida sp.
6.
Model using āplannedā model
7.
16
Evaluate modeling results/appropriateness
17.
Data Availability & Background
Exposure Route
Ingestion
Ingestion
Ingestion
Ingestion
Dermal
Pathogen
Escherichia coli
Salmonella sp.
Proteus sp.
Bacillus sp.
Staphylococcus aureus
Klebsiella sp.
Dermal/Ingestion (Klebsiella pneumoniae)
Candida sp.
Ingestion
(Candida albicans)
Pseudomonas
Dermal
aeruginosa
Dermal
Streptococcus sp.
Airborne
Aspergillus sp.
Observed in
study sites?
Y
Y
Y
Y
Y
Observed Have Dose
in rag
Response Have Best Fit
pickers? Relationship?
Model?
Y
Y
Y
Y
Y
Y
N
N/A
N/A
N
N/A
N/A
Y
Y
Y
Y
Y
Y
N
Y
Y
Y
N
N
No Data
Y
Y
Y
N
Y
N
N
Y
N
N
Frequency of microorganism occurrence:
Dump Site: S. aureus = E. coli > Salmonella spp.
Rag Pickers: S. aureus > E. coli > Salmonella spp.
17
18.
Modeling Approach
Pathogen
Status
Escherichia coli
enterotoxigenic
enteroinvasive
enteropathogenic
Salmonella Typhi
Staphylococcus aureus
Klebsiella pneumoniae
Candida albicans
# of Available
DR Models
Modeled
Modeled
Modeled
Modeled
Modeled
Modeled
(w/derived DR)
Modeled
(w/derived DR)
14
7
4
3
3
1
N/A
N/A
Planned Model
Ī²Poisson
Ī²Poisson
Ī²Poisson
Ī²Poisson
Exponential
Developed Exponential
Dose Response
Developed Exponential
Dose Response
Final Model
Reference
Exponential
Exponential
Exponential
Exponential
Exponential
QMRAwiki
Haas et al. 1999
Du Pont et al. 1971
Powell 2000
Hornick 1970
Rose et al. 1999
Exponential
See next slide
Exponential
See next slide
ā¢
Evaluated available dose response models
ā¢
Built Excel model
ā
ā¢
1000 iterations
18
19.
Approximation to exponential
model
1. Gather LD50 available in published literature
2. Substitute known values to determine k
LD50
Strain KP1O
Response k
7.20E+00 Death
Ave
Read off the
LD50 dose,
Proceed same
way as before
Stdev
9.63E02
6.50E+00 values 1.07E01 1.01E01 0.007331
3. Use determined kDeath for Monte Carlo
19
21.
Risk Characterization: Risk across
different sites
S. Typhi
C. albicans
K. pneumoniae (ingestion)
K. pneumoniae (subcutaneous)
E. coli (EIEC)
S. aureus
ā¢
Population at risk
1.00E+04
8.00E+03
6.00E+03
ā¢
4.00E+03
2.00E+03
0.00E+00
1
2
3
4
5
Dumping sites
6
7
8
ā¢
Sites 4 and 6 face risk
from >2 pathogens (i.e.,
S. Typhi, E. coli, C.
albicans & S. Typhi, E.
coli, and K.
pneumoniae)
Sites 1, 2, 3, 5 and 7
face risk from 2 types of
pathogen
Site 8 (control site) has
no known pathogenic
21
22.
Risk Characterization: Risk across
different pathogens
Dumping sites/ pathogens
1
E. coli (EIEC)
6.56E03
S. Typhi
6.07E01
S. aureus
1.36E05
Risk per year
(Maximum allowable risk = 104 or 1 in 10,000 population)
2
3
4
5
6
7
6.56E03
8
7.63E03 6.02E03 7.63E03 6.56E03 6.02E03
5.47E01 4.23E01 3.76E01 4.15E01
1.36E05
1.16E05 1.36E05 1.07E05 1.16E05 1.16E05
K. pneumoniae (ingestion)
6.37E01
1.72E01
K. pneumoniae (subcutaneous)
9.22E01
3.88E01
C. albicans
ā¢
1.00E+00
1.00E+00
6.95E06
Authorities should be more concerned of the
pathogens in descending priorities of:
C. albicans = K. pneumoniae = S. typhi > E. coli (EIEC) > S. aureus
22
23.
Sensitivity Analysis
ā¢
Sensitivity Analysis
ā
3 strains of pathogenic of E. coli
ā
3 different ratios of Pathogenic EC:EC
ā
3 different concentrations of E. coli in MSW
23
25.
Ratio of Pathogenic E. coli to E. coli
Strain
Path EC:EC
Dose
(CFU/d)
K
(estimated)
Annual
Risk
enteroinvasive
0.001
96.73
2.2*107
5.4*103
enteroinvasive
0.01
967.26
2.2*108
6.5*102
enteroinvasive
0.1
9672.60
2.2*108
1.0
f(x) = NaNx
RĀ² = NaN
12
Risk (P(I)/d)
10
8
Linear ()
6
4
Linear ()
2
0
Linear ()
1
10
Dose (mg/d)
25
26.
Study Limitations
ā¢
Quality of input microorganism data questionable
ā
ā¢
Detection methods ā described methods not sufficient for listed microorganisms
Dose response relationships
ā
Some extrapolated from animal models
ā
Doseresponse models for three of the pathogens are not available in QMRA Wiki
(Candida, Staphylococcus aureus, Klebsiella spp.)
ā¢
ā
ā¢
Estimated from LD50
Switch from Ī²Poisson to exponential model
Need to assume strains present (based on available doseresponse curves)
ā
ā
Salmonella spp. reported
ā
ā¢
Indicator E. coli reported
Most other MO reported as genus (generic) rather than specific species
Precise dumping site locations unknown
26
28.
Intervention measures
ā¢
Microbial risks:
Sites 4 and 6 > Sites 1, 2, 3, 5
and 7
ā¢
Proximity to residential
district
Sites 1, 2, 3, 4 nearer than Sites
5, 6, 7 (human flux to residential
district is impeded by the
presence of a forest reserve)
ā¢
Legend:
Dumping sites 1, 2, 3, 4 are near to the residential district
Dumping sites 5, 6 and 7 are located further away
Dumping site 8 is a control site (construction waste)
Approach 1: Encourage rag
picking activities in Sites 5
28
and 7, with a localized
29.
Intervention measures
ā¢
ā¢
C. albicans = K. pneumoniae = S. Typhi > E. coli (EIEC) > S.
aureus
Treatment removal efficiency of following should be achieved:
K. pneumoniae
S. Typhi
C. albicans
1.30E+02
6.50E+04
2log removal
4.60E01
1.52E+05
5.70E03
7.67E+04
6log removal
7log removal
0.00E+00 5.00E+04 1.00E+05 1.50E+05 2.00E+05
29
30.
Other Management Strategies
Sites
Strategies suggested
1
ā
Usage of PPE (gloves,
ā shoes, mask)
Periodic immunization,
ā medical screening
Risk communication/
ā” education at basic level
Installation of a collection
į“„ center
2
3
4
ā ā ā āā” ā ā
v
v
v
5
ā
6
āā”į“„
7
ā
# 2, 3, and 4 has high annual risk due
to Candida albicans and K.
pneumoniae.
Usage of PPE at all the sites would
reduce the dermal exposure
significantly
Risk communication strategies could
minimize secondary transmission
across subpopulations
30
31.
Future Work
ā¢
Conduct additional sampling
ā
ā
ā¢
ā¢
Concentrations on rag pickers
Proportion of pathogenic strains and identity
Check modeling assumptions
Better characterization of input variable
uncertainty
ā¢
More rigorous sensitivity analysis
ā¢
Evaluate additional dose response models
31
32.
References
ā¢
QMRA Wiki (CAMRA)
ā¢
USEPA Handbook of Exposure
ā¢
ā¢
Wachukwu C.K., Mbata C.A., Nyenke C.U.
(2010) The Health Profile and Impact
Assessment of Waste Scavengers (Rag Pickers)
in Port Harcourt, Nigeria. Journal of Applied
Sciences 10: 91681972.
Chandramohan A., Ravichandran C. (2010)
Solid waste, its health impairments32 role of
and
33.
References
ā¢
ā¢
ā¢
WennerĆ„s C, Erling V (2004) Prevalence of
enterotoxigenic Escherichia coliassociated
diarrhoea and carrier state in the developing
world. J Health Popul Nutr 22: 370382
Wingard J.R., Dick J.D., Merz W.G., Sandford
G.R., Saral R., Burns W.H. (1982) Differences in
virulence of clinical isolates of Candida
tropicalis and Candida albicans in
mice. Infection and Immunity 37: 833836.
33
Cryz Jr S.J., Furer F., Germanier R (1984)
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