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The geometric mean and 95% range for the final estimated coliphage and E. coli doses are presented in Table 7. Exposure to the highest dose of fecal microbes was estimated to occur durning scenario A. The coliphage doses had a mean of 2.44 pfu log10, while E. coli doses had a mean of 5.47 cfu log10. Scenario D estimated exposure to the lowest dose of fecal microbes with a mean of 1.39 pfu log10 of coliphage ingested and 4.80 cfu log10 of E. coli ingested. Although the E. coli concentrations in drains that were rivers/lagoons were significantly lower than the concentrations in all other drains, practically the concentrations were similar and differed by less than 1 cfu log10. When these two concentrations were applied to the exposure model, the log-transformed doses only differed by 79.6% indicating no significant difference between the two doses.

Table 7

Estimated coliphage and E. coli doses for six drain entry exposure scenarios

 log10 (coliphage, pfu)
log10 (E. coli, cfu)
Exposure scenarioGeo mean95% rangeGeo mean95% range
Children under 5 years (A) Accidentala 2.44 –0.99, 5.50 5.47 2.31, 8.22 
(C) Incidentalb 1.54 –1.88, 4.65 4.94 1.69, 7.75 
(E) Deliberatec 2.40 0.05, 4.86 5.43 3.41, 7.57 
Children 5–12 years (B) Accidentala 2.29 –1.40, 5.52 5.32 1.87, 8.22 
(D) Incidentalb 1.39 –2.39, 4.63 4.80 1.33, 7.75 
(F) Deliberatec 2.39 0.04, 4.84 5.42 3.40, 7.54 
 log10 (coliphage, pfu)
log10 (E. coli, cfu)
Exposure scenarioGeo mean95% rangeGeo mean95% range
Children under 5 years (A) Accidentala 2.44 –0.99, 5.50 5.47 2.31, 8.22 
(C) Incidentalb 1.54 –1.88, 4.65 4.94 1.69, 7.75 
(E) Deliberatec 2.40 0.05, 4.86 5.43 3.41, 7.57 
Children 5–12 years (B) Accidentala 2.29 –1.40, 5.52 5.32 1.87, 8.22 
(D) Incidentalb 1.39 –2.39, 4.63 4.80 1.33, 7.75 
(F) Deliberatec 2.39 0.04, 4.84 5.42 3.40, 7.54 

pfu denotes plaque forming units; cfu denotes colony forming units.

(A)–(F) indicates exposure scenario.

aAccidental drain entry describes a scenario where a child fell into a drain, had hand contact with drain water and subsequent hand mouthing events occurred.

bIncidental drain entry describes a scenario where a child entered a drain to retrieve a fallen object, had contamination of their hands through the object and subsequent hand mouthing events occurred.

cDeliberate drain entry describes a scenario where a child purposefully entered a drain for a period of time in which their hands could contact drain water and subsequent hand mouthing events occurred. It was assumed at least a droplet of drain water was ingested per deliberate entry event.

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