Irrigation water has been recognized as an important microbial risk factor for fruits and vegetables in many production areas, but there is still a lack of information about how the microbiological quality of different irrigation water sources and climatic conditions influence the safety of vegetables produced in Brazil. This study evaluated the distribution of generic E. coli and the prevalence of E. coli O157:H7 in two different water sources (ponds and streams bordering farmlands and urban areas) used for irrigation and on commercially produced lettuces in Southern Brazil. We also evaluated the effect of agricultural factors and meteorological conditions in the potential contamination of water and produce samples. A longitudinal study was conducted on four farms during a year (July 2014 to August 2015). The results showed generic E. coli prevalence of 84.8% and 38.3% in irrigation water samples and on lettuces, respectively, indicating irrigation water as an important source of contamination of lettuces. No significant differences were detected in the counts of E. coli between the two different surface water sources. The climatic conditions, particularly rainfall and environmental temperature, have influenced the high concentration of E. coli. The highest loads of E. coli in irrigation water and on lettuces were found during the warmest time of the year. E. coli O157:H7 was detected by qualitative polymerase chain reaction (qPCR) in 13 water samples but only 4 were confirmed by isolation in culture media.

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Reclaimed water obtained from urban wastewater is currently being used as irrigation water in water‐scarce regions in Spain. However, wastewater can contain enteric viruses that water reclamation treatment cannot remove or inactivate completely. In the present study, greenhouse‐grown baby lettuce (Lactuca sativa L.) was irrigated with secondary treatment effluent from a wastewater treatment plant untreated and treated using chlorine dioxide (ClO2). The effect of ClO2 treatment on the physicochemical characteristics and the presence of enteric viruses in irrigation water and lettuce was assessed. The presence of human noroviruses genogroups I and II (NoV GI and NoV GII), and human astroviruses (HAstV), was analyzed by real‐time polymerase chain reaction (RT‐qPCR). Additionally, to check for the loss of infectivity induced by the disinfection treatment, positive samples were re‐analyzed after pretreatment with the intercalating dye PMAxx before RNA extraction and RT‐qPCR. There were no significant differences in the proportion of positive samples and the concentration of enteric viruses between treated and untreated reclaimed water without PMAxx pretreatment (p > 0.05). A significantly lower concentration of NoV GI was detected in ClO2–treated water when samples were pretreated with PMAxx (p < 0.05), indicating that inactivation was due to the disinfection treatment. Laboratory‐scale validation tests indicated the suitability of PMAxx‐RT‐qPCR for discrimination between potentially infectious and ClO2–damaged viruses. Although the applied ClO2 treatment was not able to significantly reduce the enteric virus load of the secondary effluent from the wastewater treatment plant, none of the lettuce samples analyzed (n = 36) was positive for the presence of NoV or HAstV. Core Ideas Reclaimed water used for irrigation can contain enteric viruses. Current detection methods do not distinguish infectious from noninfectious viruses. PMAxx treatment can help to get information on the infectivity of viral particles. Treatment of reclaimed water with ClO2 did not improve irrigation water safety.

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