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S R Petterson

Publications and source records attributed to S R Petterson.

5 recordsLinked to original sources
PubMed2001

Modeling virus inactivation on salad crops using microbial count data.

Microbial counts of the persistent Bacteroides fragilis bacteriophage B40-8 from a virus decay experiment conducted under glasshouse conditions were used to model the decay of viruses on wastewater-irrigated lettuce and carrot crops. The modeling approach applied gave specific consideration to the discrete nature of microbial count data. The experimental counts were best fit by a negative binomial distribution indicating highly dispersed distribution of viruses on lettuce and carrot crops following irrigation with wastewater. In addition, there was evidence for biphasic inactivation of viruses, signifying the presence of a persistent subpopulation of viruses that decayed slowly, resulting in virus accumulation on the crop surface over subsequent irrigations. Maximum likelihood estimates of initial and persistent subpopulation inactivation rates were 2.48 day(-1) and 0.51 day(-1) for lettuces and 0.84 day(-1) and 0.046 day(-1) for carrots. Maximum likelihood estimates of the persistent virus subpopulation size were 0.12% and 2% for lettuce and carrots, respectively.

Agriculture↗
PubMed2001

Viral risks associated with wastewater reuse: modeling virus persistence on wastewater irrigated salad crops.

A model for virus decay on lettuce and carrot crops has been derived as part of a comprehensive wastewater irrigation microbial risk assessment model under development. Results from the decay modeling indicated the presence of a very persistent sub-population of viruses evidenced by an initial rapid phase of decay followed by a very slow phase. In addition, virus counts fitted a negative binomial rather than Poisson distribution indicating over-dispersion. Hence the data indicated that viruses were not uniformly distributed over the surfaces of both crops. The aim of this paper was to investigate the implications of over-dispersion and the presence of a very persistent sub-population of viruses for assessing viral illness from the consumption of lettuces and carrots irrigated with secondary treated effluent. When over-dispersion or clumping of viruses was accounted for, a significant increase in the heterogeneity in the risk estimates arose. In addition, predicted infection rates were significantly underestimated if the presence of a persistent sub-population of viruses was not considered in the decay kinetics of the risk model. Hence, both viral clumping and persistence sub-populations should be accounted for in future risk assessments of enteric viruses associated with wastewater reuse.

Agriculture↗
PubMedDate not supplied

Microbial risks from wastewater irrigation of salad crops: a screening-level risk assessment.

The potential health risk from viruses, associated with the consumption of lettuce crops spray irrigated with secondary-treated municipal effluent, has been evaluated in the first level investigation of a tiered microbial risk assessment. The study assessed the impact of two factors on the estimated risk of infection: a suitable probability density function for the occurrence of human enteroviruses in irrigation water and appropriate die-off rates for viruses on lettuce crops. A Monte Carlo simulation using a log-normal and a nonparametric, kernel estimated probability density function indicated that slight changes in the upper tail of the probability density function had a relatively low effect on the estimated infection rates. Predicted infection rates were much more sensitive to the decay rate of viruses than occasional high virus numbers. The median and 99th percentile risks of infection from the overall model were 0.10 and 0.51/10000 lettuce consumers, respectively, indicating possible human health concern, and the justification of a more detailed microbial risk assessment.

Agriculture↗