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Exposure at the simplest level is the dose of the pathogen that an individual ingests (eg. number of noroviruses), inhales (eg. numbers of bacteria cells of Legionella), or comes in contact with (eg. numbers of skin bacterial pathogens such as Staphylococcus). This number feeds into the dose-response models to predict the probability of infection. However exposure assessment is very complex and involves a combination of addressing the methods used to measure the microbes and the concentrations in the water or air for example, as well as the timing of the exposure. In most cases exposure can be viewed as a pathway from the source of the pathogen (eg shedding of pathogens by infected individuals, or concentrations in sewage) to the actual exposure (swimming at the beach). This also involves understanding the transport and survival of the microbe.
Exposure is often venue or media specific. Federal agencies such as EPA and FDA have developed long term programs to collect and accrue large amounts of data on populations exposures to drinking water and types of food often separated by age. EPA Exposure Factors Handbook
This section will begin to collect and present the parameters which are associated with exposures for water and fomites and will include pathogen specific parameters.
- Pathogen excretion from infected individuals or populations
- Pathogen occurrence and concentrations in various sources
- Pathogen inactivation over time on various surfaces, in water
- Amount of air inhaled, water ingested
Fomites are any nonliving surface that can harbor a pathogen. Fomites are experienced and encountered everyday and are typically more commonly encountered than other exposure routes, such as drinking water. When developing a QMRA for fomites, there are a number of key pieces of information and data that need to be addressed. First the pathogen survival on fomites must be addressed, this available data that has been used in past QMRAs by CAMRA and non CAMRA investigators. In the fomite page the following parameters are summarized and described:
- Survival of pathogens on fomites are as decay rates of the pathogens, this does not include chemical inactivation of the pathogens. This data is summarized for Category A agents at this moment.
- Transfer efficiency from fomite to hands, in terms of percent of pathogens transferred from a fomite to a finger.
- Transfer efficiency from hands to mouth, in terms of percent of microorganisms transferred from human fingers to the mouth.
- Contact rates for humans, where the number of hand-to-face behavior is quantified
Human Specific Parameters
a In this study, a high isolation rate of different enteropathogens, e.g. Shigella flexneri, Shigella boydii,Salmonella typhimurium, Enteroagrregative E. coli, Enteropathogenic E. coli, Aeromonus sp. and rotavirus was observed.
b Shigella, E. coli, Proteus, Pseudomonas aeruginosa were identified from the subjects.
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Pathogen Excretion Rate
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