application of qmra in waterborne...

FIRST INTERNATIONAL SYMPOSIUM ON FOOD SAFETY

“Application of QMRA in waterborne pathogens”

Aiko Adell NakashimaSchool of Veterinary Medicine

Faculty of Ecology and Natural ResourcesUniversidad Andres Bello

E-mail: [email protected]

Quantitative Microbial Risk Assessment (QMRA)

Methodology used to:

- Estimate risk and consequences from an exposure of individuals or population to

infectious organisms.

Allowing resources and efforts to be focused in prioritized ways to reduce risks

- Identify situations that contribute to an increased risk of illness

QMRA OBJECTIVES

Aim of QMRA:

Management and comunication.

Help directors, managers, shareholders, public services, individuals, etc. to understand the risk and opportunities.

Evaluate the available options to control those risks

QMRA: 4 STEPS

1) Hazard Identification 2) Dose-Response Assessment

3) Exposure Assessment: 4) Risk Characterization

Step 1

Step 2

Step 3=

QMRA– TOOLS

1. SPREADSHEETS (EXCEL).

@RISK (Palisade)

Crystal Ball (Oracle)

ModelRisk (Vose)

FONDECYT INICIACION PROJECT:

The impact of land use on the fecal sources of contamination of rivers and on human and

animal health risks

(Project ID: 11160116)

1. Hazard Identification


• WHO 2015: 31 foodborne hazards have caused 600 million illness and 420,000 deaths. Diarrhea disease agents: 230,000 deaths.

• Chile

WHO 2015, http://apps.who.int/iris/bitstream/10665/199350/1/9789241565165_eng.pdf?ua=1Prado, VJ, et al. 2002. Rev. med. Chile. 130 (5): 495 -501Olea , A et al. 2012. Rev Chilena Infectol. 29(5):504-10Thomas MK, et al. 2011. Epidemiol. Infect. (2011): 139, 560–571

Year N° of Outbreaks Incidence rate Reference

1999 190 7.5 Prado et al., 2002

2000 260 8.2 Prado et al., 2002

2005-2010 5,689 Olea et al, 2012

0.98–2.3 episode per person-year

Thomas et al., 2011


• Gastrointestinal Illness (GI) caused by parasites in Chile:

• Giardia duodenalis: prevalence + 20-30% - principal cause of diarrhea in children (Tassara, 1999).

• 2008-2012: 1,392 children diarrhea = 183 (13,1%) positive samples = Blastocystus hominis , Giardia duodenalis and Cryptosporidium spp (ISP 2012).

• Water related Outbreaks:

US: >50 cryptosporidiosis outbreaksin humans

• No treatment for Cryptosporidium• Tassara R. 1999. Pediatria. 1999; 70 (5): 441 -445 / ISP. 2012. URL: http://www.ispch.cl/sites/default/files/boletin_diarreas.pdf

Infection/illness: small doses (10 oocysts)

Adapter for waterborne transmission:

Excreted in large quantities

Resistant to environmental conditions

Chloride resistant

Oocysts (Cry) and cysts are immediately infective after being excreted

Protozoa: Cryptosporidium, Giardia Public Health Importance

2. Exposure Assessment:

Cryptosporidium/ Giardia

Viable (oo/cysts) Not Viable (oo/cysts)

Exposure: Water Ingestion

Water Source: River

Dilution Factor

Human

Fecal Coliforms + E. coli

Bacteroidales

Estimate contamination

MST

Other studies

Estimation of oocysts / cysts ingested by humans:

2. Exposure Assessment:

Conversion from 10 L to 1 mL

Dilution Factor:• 1:1• 1:30

Bacteroidales (%)

Protozoa viability• 100%• 0.1%

Water ingestion (ml)

Protozoa Concentration in 10L*

Own data

Own data

*Adjusted for recovery % and detection limit

2) Dose-Response Assessment

Exposition routes: Ingestion, inhalation, contact

Final result: Infection or Illness

Dose response Studies:

Mild-virulent agents: healthy adult humans

Cryposporium parvum: Okhuysen et al. 1999; Okhuysen et al. 2002, Chappell et al, 2006; etc

Giardia: Rendtorff (1954), and Rendtorff and Holt (1954)

Animal models


Independent action theory:

One organism is capable of initiating illness

But, as the probability of evading the host defenses and causing infection is low,

More than one microorganism is required to cause infection

QMRA supports this theory: to determine the probability that one microorganism cause disease:

Models: Beta Exponencial Log probit

http://qmrawiki.canr.msu.edu/index.php?title=Table_of_Recommended_Best-Fit_Parameters

d = oocysts and cysts dose given to an individual (it is not a median dose)

r = probability that only one protozoa is able to cause infection

The distribution of microorganism that survive (and cause infection) is binomial when each one of the ingested dose (d) has a probability of surviving (r) equal or identical (Haas, 2002)*

*Haas, C.N., 2002, Conditional dose-response relationships for microorganisms: Development and application. Risk Anal 22, 455-463.


Binomial Model

1. Cryptosporidium (Teunis, 2009)

Okhuysen et al. 1999; Okhuysen et al. 2002, Chappell et al, 2006

ID50 = 35 oocysts


II. Giardia (Rose and Gerba, 1991)

Rendtorff (1954) and Rendtorff and Holt (1954)

r = 0.01982

Dose response curve for humans:

4. Risk Characterization

¿What is acceptable?

EPA criteria for humans:

32 illness/1,000 individuals or 3.2%

Percent of infections resulting in illness: 50% for Cryptosporidium and 45% for Giardia (Soller et al. (2010)

Results:

Humans: Probability of illness

Soller, J.A., Schoen, M.E., Bartrand, T., Ravenscroft, J.E., Ashbolt, N.J., 2010. Water Res. 44, 4674e4691

Pathogens are randomly distributed in water

Oocysts and cysts do not multiply in the environment

Viability is not the same as infectivity

A single pathogen can survive the host's defenses and reach the site where the infection develops

The survival of a pathogen is independent of the presence of another pathogen

Humans are healthy and immunocompetent individuals

Human will be exposed once to the contaminated water

Secondary infection won´t occur


Assumptions

Statistical Methods

@ Risk

Stochastic models using MonteCarlos simulation

Sensitivity Analysis: what variables in the model have a higher impact on the result


6. Results

Sensitivity Analysis

More Important Less Important

Protozoa ConcentrationBacteroidales (%)

Water IngestedSwimming durationSea otter body weight

Search for a risk range when the exposition is known orassumed: X pathogen has been detected during thesampling of a specific finished food. What level of riskwould the consumers have?

Evaluation of HACCP systems

Evaluate mitigation measures in the processing of a food: temperature, etc.

Estimate the risk of a population that consumes a specific food containing X amount of the microorganismY

Some applications of QMRA in Food Safety

Many thanks to:

María Cristina MartínezISP

Woutrina SmithUniversity of California, Davis

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