Estimation of norovirus infection risks to consumers of wastewater-irrigated food crops eaten raw.
A quantitative microbial risk analysis-Monte Carlo method was used to estimate norovirus infection risks to consumers of wastewater-irrigated lettuce. Using the same assumptions as used in the 2006 WHO guidelines for the safe use of wastewater in agriculture, a norovirus reduction of 6 log units was required to achieve a norovirus infection risk of approximately 10(-3) per person per year (pppy), but for a lower consumption of lettuce (40-48 g per week vs. 350 g per week) the required reduction was 5 log units. If the tolerable additional disease burden is increased from a DALY (disability-adjusted life year) loss of 10(-6) pppy (the value used in the WHO guidelines) to 10(-5) pppy, the required pathogen reduction is one order of magnitude lower. Reductions of 4-6 log units can be achieved by very simple partial treatment (principally settling to achieve a 1-log unit reduction) supplemented by very reliable post-treatment health-protection control measures such as pathogen die-off (1-2 log units), produce washing in cold water (1 log unit) and produce disinfection (3 log units).
Mara
Duncan
D
Institute for Pathogen Control Engineering, School of Civil Engineering, University of Leeds, Leeds LS2 9JT, UK. d.d.mara@leeds.ac.uk
Sleigh
Andrew
A
D017250:Caliciviridae Infections / Q000821:virology*; D003296:Cooking; D005516:Food Microbiology; D006801:Humans; D018545:Lactuca / Q000821:virology*; D008954:Models, Biological; D009010:Monte Carlo Method; D029322:Norovirus; D012307:Risk Factors; D014865:Waste Disposal, Fluid