title: Modeling the die-off of E. coli and Ascaris in wastewater-irrigated vegetables: implications for microbial health risk reduction associated with irrigation cessation.
abstract: This study assessed the die-off of Escherichia coli (E. coli) and Ascaris suum on lettuce (Great Lakes 118) and cabbage (Brassica oleracea var capitata) in wastewater-irrigated fields using comparative mathematical die-off models. The study revealed that none of the survival curves of E. coli and A. suum was best fitted with the log-linear model, indicating that the classical first-order kinetic approach is inadequate in many cases. The biphasic die-off model best described the die-off of E. coli on lettuce (kmax1 = 2.62 day(-1) and kmax2 = 0.22 day(-1)) and cabbage (kmax1 = 1.06 day(-1) and kmax2 = 0.53 day(-1)). The die-off of A. suum on lettuce was best described by the biphasic model (kmax1 = 0.48 day(-1) and kmax2 = 0.01 day(-1)) and best described by log linear + tail (kmax = 0.44) on cabbage. A comparative health risk assessment associated with the consumption of lettuce showed significant underestimation of the number of days of irrigation cessation required to achieve E. coli O157:H7 and Ascaris tolerable annual infection risk when using biphasic die-off rates compared with other die-off rates. The study stresses the need to test different die-off models as inputs for quantitative microbial risk assessment (QMRA) particularly for interventions associated with health risk reduction.
authors.affiliation: Water, Sanitation Engineering and Health Group, Department of Mathematical Sciences and Technology, Norwegian University of Life Sciences, Postboks 5003, N-1432, Ås, Norway E-mail: razaks@umb.no; razseidu@yahoo.co.uk.
authors.forename: Razak
authors.initials: R
authors.lastname: Seidu
authors.forename: Ingrid
authors.initials: I
authors.lastname: Sjølander
authors.forename: Amina
authors.initials: A
authors.lastname: Abubakari
authors.forename: Dennis
authors.initials: D
authors.lastname: Amoah
authors.forename: John A
authors.initials: JA
authors.lastname: Larbi
authors.forename: Thor Axel
authors.initials: TA
authors.lastname: Stenström
mesh_terms: D057914:Agricultural Irrigation; D000818:Animals; D001200:Ascaris / Q000302:isolation & purification*; D001937:Brassica / Q000382:microbiology / Q000469:parasitology; D004926:Escherichia coli / Q000302:isolation & purification*; D005506:Food Contamination; D005516:Food Microbiology; D018545:Lactuca / Q000382:microbiology / Q000469:parasitology; D014675:Vegetables / Q000382:microbiology* / Q000469:parasitology*