Exposure assessment

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General Overview

Exposure assessment involves a combination of methods and parameters to determine the dose of pathogens that hosts are exposed to. Aspects include:

  • Shedding of pathogens by infected individuals
  • Inactivation of pathogens over time on various surfaces, in water, or in food
  • Transfer of pathogens between hands and objects
  • Amount of air inhaled, water ingested, or foods ingested
  • Settling of pathogens suspended in fluids

Water Exposure

Drinking Water Exposure

For a more complete description of the drinking water environment please refer to the Drinking Water page

Table 1: Per capita estimates of combined direct & indirect water ingestion from community water (mL/day)a
Age Sample Size Mean (mL/day)
Infant (<1 year) 1486 327
Children (1-16 years) 9162 397
Adult (>16 years) 12129 1088

a Detailed data is given on page 3-25 of Chapter 3 in the EPA Exposure Factors Handbook


Children's ingestion rate for 4-8 years of age is 1,363 +/- 333 ml per day (mean +/- standard deviation) as given on page 3-64 of Chapter 3 in the EPA Exposure Factors Handbook

Recreational Water

For a more complete description of the recreational water environment please refer to the Recreational Water page

Table 2: Pool water ingestion by swimmersb
Age Sample Size Mean (mL/45-minute)
Children (<16 years) 41 37
Males (<16 years) 20 45
Females (<16 years) 21 30
Adults (>18 years) 12 16
Men 4 22
Women 8 12

b Detailed data is given on page 3-81 of Chapter 3 in the EPA Exposure Factors Handbook

Wastewater

For a more complete description of the wastewater environment please refer to the Wastewater page

Pathogen Specific

  • Regrowth
  • Shedding
Healthy population fecal output
1. Healthy Nigerian children aged 6 months to 5 years: mean 109.3 mL of stool per day (SD: 54.07). (Akinbami et al. 1995).
2. Healthy Nigerian adult (medical students): mean wet weight of 143.3 g stool per day (SD: 48.5), and an average of 0.89 stools per day.
E. coli H 10407
Healthy adult volunteers following ingestion of 108 organisms given with NaHCO3: excreting approximately 107 - 109 E. coli H 10407 organisms per gram of stool till day 7 (Levine et al. 1980).
Enteropathogenic E. coli
Adult infected with EPEC: average stool weight 406.3 g per day (SD: 300.2). The peak excretion of the challenge strain was 108 CFU per gram of stool (Donnenberg et al. 1993).
Diarrhea general
1. 3-24 month children with diarrhea: During initial 24h and rehydration period, mean stool output was 126 (SD 33.6) grams of feces per kilogram body weight per hour (Dutta et al. 2000)
2. Adult Tunisian with acute diarrhea: mean stool weight 499 g per day (SD: 284) (Hamza et al. 1999)
  • Survival
When pseudo first-order die-off kinetics were assumed, the die-off rate of oocysts at 5°C was 0.010 log10/d and at 15°C, 0.006–0.024 log10/d in river water. In untreated river water, the die-off of E coli and enterococci was approximately 10x faster than die-off of oocysts but die-off rates of C perfringens were lower than those of oocysts (Medema et al. 1997).
  • Transport

Case Studies

Air Exposure

Indoor Air

Outdoor Air

Pathogen Specific

Case Studies

Tao Hong, Yin Huang, Patrick L. Gurian and Charles N. Haas have completed a manuscript with complete fate and transport model coupled with dose response for indoor air release and fomite interaction of office inhabitants

Fomites

Ingestion

Membranes

Cutaneous


Besides exposure assessment, the other major components of microbial risk assessment are hazard identification, dose response assessment, and risk characterization.


References

EPA Exposure Factors Handbook

Akinbami, F., Erinoso, O. and Akinwolere, O. (1995) Defaecation pattern and intestinal transit in nigerian children. African Journal of Medicine and Medical Sciences 24, 337-341. Abstract

Donnenberg, M., Tacket, C., James, S., Losonsky, G., Nataro, J., Wasserman, S., Kaper, J. and Levine, M. (1993) Role of the eaea gene in experimental enteropathogenic escherichia coli infection. Journal of Clinical Investigation 92, 1412-1417. Full text

Dutta, P., Dutta, S., Manna, B., Chatterjee, M. and De, A. (2000) Hypo-osmolar oral rehydration salts solution in dehydrating persistent diarrhoea in children: Double-blind, randomized, controlled clinical trial. Acta Paediatrica 89, 411-416. Full text

Hamza, H., Ben Khalifa, H., Baumer, P., Berard, H. and Lecomte, J.M. (1999) Racecadotril versus placebo in the treatment of acute diarrhoea in adults. Alimentary Pharmacology and Therapeutics 13, 15-19. Full text

Levine, M., Rennels, M., Cisneros, L., Hughes, T., Nalin, D. and Young, C. (1980) Lack of person-to-person transmission of enterotoxigenic escherichia coli despite close contact. American Journal of Epidemiology 111, 347-355. Full text

Medema, G.J., Bahar, M. and Schets, F.M. (1997) Survival of cryptosporidium parvum, escherichia coli, faecal enterococci and clostridium perfringens in river water: Influence of temperature and autochthonous microorganisms. Water Science and Technology 35, 249-252.

Sobsey, M., Stauber, C., Casanova, L., Brown, J. and Elliott, M. (2008) Point of use household drinking water filtration: A practical, effective solution for providing sustained access to safe drinking water in the developing world. Environmental Science & Technology 42, 4261-4267.