Defining Susceptibility for Microbial Risk Assessment: Results of a Workshop

Abstract

An interdisciplinary workshop was convened by the George Washington University in June 2001 to discuss how to incorporate new knowledge about susceptibility to microbial pathogens into risk assessment and management strategies. Experts from government, academic, and private sector organizations discussed definitions, methods, data needs, and issues related to susceptibility in microbial risk assessment. The participants agreed that modeling approaches need to account for the highly specific nature of host-pathogen relationships, and the wide variability of infectivity, immunity, disease transmission, and outcome rates within microbial species and strains. Concerns were raised about distinguishing between exposure and dose more clearly, interpreting experimental and outbreak data correctly, and using thresholds and possibly linearity at low doses. Recommendations were made to advance microbial risk assessment by defining specific terms and concepts more precisely, designing explicit conceptual frameworks to guide development of more complex models and data collection, addressing susceptibility in all steps of the model, measuring components of immunity to characterize susceptibility, reexamining underlying assumptions, applying default methods appropriately, obtaining more mechanistic data to improve default methods, and developing more biologically relevant and continuous risk estimators. The interrelated impacts of selecting specific subpopulations and health outcomes, and of increasing model complexity and data demands, were considered in the contexts of public policy goals and resources required. The participants stated that zero risk is unattainable, so targeted and effective risk reduction and communication strategies are essential not only to raise pubic awareness about water quality but also to protect the most susceptible members of the population.

Escherichia coli in the Environment: Implications for Water Quality and Human Health

“…Moreover, linking MST studies and potential human health hazards is a challenging but important topic. The construction of microbial risk models is necessary to assess potential human health hazards 6) . For accurate modeling, however, future studies are needed to clarify the distribution of these pathogens in animals and the environment, and the evolutionary and ecological forces leading to their establishment in humans, animals and environmental niches.…”

Do we all face the same risk when bathing in the estuary?

“…Risk in recreational waters was addressed using such a model in Soller et al (2003). However, children should be taken into separate consideration in QMRA (Nwachuku and Gerba, 2004) as they may display attack rates higher than adults when swallowing water and submerging their head (Balbus et al, 2004). Age has also been investigated as the primary determining factor related to the type and severity of health outcomes from enterovirus exposures in recreational waters ; however, limited data on this subject are currently available in the peer review literature.…”

Valuing Water, Valuing Livelihoods: Guidance on Social Cost-benefit Analysis of Drinking-water Interventions, with Special Reference to Small Community Water Supplies

“…There are many possible definitions of vulnerability and susceptibility (Balbus et al, 2004). For the purposes of this discussion, a vulnerable group is considered to be composed of people who may be at increased risk of suffering an illness or may have more severe outcomes should they be affected.…”