U.S. EPA and DHS Center of Excellence. CAMRA is an interdisciplinary research center established to develop scientific knowledge on the fate and risk from high priority infectious agents.
CAMRA is an interdisciplinary research center established to develop scientific knowledge on the fate and risk from high priority infectious agents.
(Michigan State University, Drexel University, University of Michigan, Carnegie Mellon University, Northern Arizona University, University of Arizona and University of California Berkeley)
Joan B. Rose, Ph.D., Yin Huang, Ph.D.
Michigan State University
A method for assessing risks from microbial agents in a framework that defines the statistical probability of an infection from the environmental pollution of water, soil, food, surfaces and hands
The problem should be formulated to respond directly to the needs of decision makers, stakeholders, as well as the interested public, and to guide the risk assessment paradigm
- End point: infection, illness or death
- Dose: number of organisms ingested or inhaled
time, and route of exposure
Establish policies for protection of health using standards or performance based criteria
- protozoan parasite
- environmentally transmissible form:
- exposure route: fecal-oral
- Risk analysis scenario: swimming
in contaminated pool
Exponential model fit to data on oral exposure to oocysts and infectivity of Cryptosporidium in humans (Dupont 1995)
i. 0.016 liters consumed per swim (Dufour et al. 2006)
ii. assume 15 infective oocysts/liter
iii. Dose =0.016 liters/swim x 15 oocysts/liter = 0.24
- Risk = 1-exp(-0.00419 x dose )
- Risk = 1-exp(-0.00419 * 0.24)= 0.0010
Seasonal Risk of swimming [probability of infection with multiple exposures] assumes each exposure event is independent.
Seasonal swimming occurs for 8 events throughout the year.
Probability of Infection for one swim event = 0.0010
Multiple Exposure Risk =1-[1-SingleRisk]8
Seasonal Swim Risk =1-[1-0.0010]8= 0.0080
generate Ln [average concentration] from normal generator in excel
After a fecal accident risks are as high as 1% with 15 oocysts/liter. Higher levels of contamination are possible and would result in significantly higher risks.
In order to reduce the risk, pools should be closed, and the water filtered and disinfected (eg with UV disinfection) to reduce the risk.