Application of QMRA  and BST to Assess the Associated Human Health Risks from Multiple Fecal Sources During Recreation 

in the Leon River Watershed

Anna GitterM.S. WMHS CandidateGraduate Research Assistant-TWRITexas A&M University

Leon River Watershed

What is the human health risk for a GI illness when you have a mixture of fecal sources in a waterbody?

• LEO 2: • Walnut Creek• 163 cfu/ 100 mL E. coli

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Water Quality and Human Health

• 2012: GI illness redefined from HCGI to NGIo Acceptable NGI risk level: 0.036o Redefined to include viral illnesses

• Prior research has found different levels of risk depending on the fecal sourceo Human v. non-human sources

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U.S. EPA, 2012. Recreational Water Quality Criteria. Office of Water, Washington D.C., 820‐F‐12‐058.

Quantitative Microbial Risk Assessment

Hazard Identification

Dose Response

Exposure Assessment

Risk Characterization

Risk Management

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Reference Pathogens• Each source represented by a reference pathogen

o Health output: GI illnesso Pathogens selected represent majority of non-foodborne GI illnesseso No dose-response model for E. coli

Sources Reference Pathogen

Human Norovirus

Cattle/Domestic Animals Campylobacter

Wildlife Cryptosporidium

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Dose Ingested• Variables in the Dose Formula

o Volume of water ingestedo Density of E.coli and reference pathogen in waste (for

each source)o Infectious prevalence and potential of each reference

pathogeno E. coli data

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Risk ScenariosSimulations Descriptions

Scenario 1Each source contributes to 100%(each source contribution tested independently)

Scenario 2

Each source contributes according to BST results • 10% human (including unidentified)• 25% cattle/domestic animals• 65% wildlife

Scenario 2 Modified

Each source contributes according to modified BST results (separating cattle and domestic animals)

• 7% human • 20% cattle• 73% wildlife/domestic animals (including 

unidentified)

Scenario 3Each source contributes equally to the bacteria load (33.3%)

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Each Source Contributing 100% of the 

Bacteria Load

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Human Cattle/DomesticAnimals

Wildlife Human Cattle/DomesticAnimals

Wildife

Tot

al P

roba

bilit

y of

GI I

llnes

s

Pathogen Contributing Sources

LEO 2 (163 cfu/100 mL) Rec Standard (126 cfu/ 100 mL)

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Risk of GI Illness: BST Percentages

0.1

0.25

0.65

0.28

0.07

0.02

0.28

0.09

0.02

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Pathogen Contributing Sources Source Specific Risk for Site LEO 2 Source Specific Risk for the Rec Standard

Risk of a G

I IllnessPr

opor

tion

of E

ach

Sour

ce C

ontr

ibut

ing

to th

e W

ater

body

Wildlife (Cryptosporidium) Human (Norovirus) Cattle/Domestic Animals (Campylobacter)

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Risk of GI Illness: Modified BST Percentages (separated cattle from domestic animals)

0.07

0.2

0.73

0.27

0.06

0.02

0.27

0.08

0.02

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Pathogen Contributing Sources Source Specific Risk for Site LEO 2 Source Specific Risk for the RecStandard

Risk of a G

I IllnessPr

opor

tion

of E

ach

Sour

ce C

ontr

ibut

ing

to th

e R

isk

Cattle (Campylobacter) Human (Norovirus) Wildlife/Domestic Animals (Cryptosporidium)

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Risk of GI illness: Each Source Contributes 33.3%

0.333

0.333

0.333

0.3

0.07

0.01

0.29

0.1

0.01

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Pathogen Contributing Sources Source Specific Risk for Site LEO 2 Source Specific Risk for Rec Standard

Risk of a G

I IllnessPr

opor

tion

of E

ach

Sour

ce C

ontr

ibut

ing

to th

e W

ater

body

Cattle/Domestic Animals (Campylobacter) Wildlife (Cryptosporidium) Human (Norovirus)

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Comparison of Risks

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

LEO 2 Rec Standard LEO 2 Rec Standard LEO 2 Rec Standard

Scenario 2 Modified Scenario 2 Scenario 3

Tot

al P

roba

bilit

y of

GI I

llnes

s

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Assumptions Contributing Uncertainty

• Need research in:o Zoonotic pathogens: potential for human infection and prevalence of infection

• Campylobacter• Cryptosporidium spp.• Other Pathogens to consider: Giardia, Salmonella enterica, E. coli 0157:H7

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QMRA Results• Proportion of a source contributing not an indicator of the

human health risk o Risk was driven by human source

• Calculated human health risk exceeded recreational risk standardo Risk primarily driven by norovirus infection and illness

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Implications• Management efforts toward reducing human source

o WWTP compliance, septic system maintenance

• Value of using BST and QMRA to quantify the human health risko Developing site-specific standards

• Prioritize sites according to the human health risko Add to the water management “toolbox”

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Thank you!

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