Risk-based water quality thresholds for coliphages in surface waters: effect of temperature and contamination aging

Abstract This study assessed the risks posed by noroviruses (NoVs) in surface water used for drinking, domestic, and recreational purposes in South Africa (SA), using a quantitative microbial risk assessment (QMRA) methodology that took a probabilistic approach coupling an exposure assessment with four dose-response models to account for uncertainty. Water samples from three rivers were found to be contaminated with NoV GI (80–1,900 gc/L) and GII (420–9,760 gc/L) leading to risk estimates that were lower for GI than GII. The volume of water consumed and the probabilities of infection were lower for domestic (2.91 × 10−8 to 5.19 × 10−1) than drinking water exposures (1.04 × 10−5 to 7.24 × 10−1). The annual probabilities of illness varied depending on the type of recreational water exposure with boating (3.91 × 10−6 to 5.43 × 10−1) and swimming (6.20 × 10−6 to 6.42 × 10−1) being slightly greater than playing next to/in the river (5.30 × 10−7 to 5.48 × 10−1). The QMRA was sensitive to the choice of dose-response model. The risk of NoV infection or illness from contaminated surface water is extremely high in SA, especially for lower socioeconomic individuals, but is similar to reported risks from limited international studies.

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Quantitative Microbial Risk Assessment for Escherichia coli O157 on Lettuce, Based on Survival Data from Controlled Studies in a Climate Chamber

Journal of Food Protection ◽

10.4315/0362-028x.jfp-10-563 ◽

2011 ◽

Vol 74 (12) ◽

pp. 2000-2007 ◽

Cited By ~ 31

Author(s):

JAKOB R. OTTOSON ◽

KARIN NYBERG ◽

ROLAND LINDQVIST ◽

ANN ALBIHN

Keyword(s):

Escherichia Coli ◽

Water Quality ◽

Risk Assessment ◽

Light Intensity ◽

Risk Reduction ◽

Escherichia Coli O157 ◽

Quantitative Microbial Risk Assessment ◽

Climate Chamber ◽

Microbial Risk Assessment ◽

Microbial Risk

The aims of the study were to determine the survival of Escherichia coli O157 on lettuce as a function of temperature and light intensity, and to use that information in a screening-level quantitative microbial risk assessment (QMRA) in order to evaluate risk-reducing strategies including irrigation water quality guidelines, rinsing, and holding time between last irrigation and harvest. Iceberg lettuce was grown in a climate chamber and inoculated with E. coli O157. Bacterial numbers were determined with the standard plate count method after inoculation and 1, 2, 4, and 7 day(s) postinoculation. The experiments were carried out at 11, 18, and 25°C in light intensities of 0, 400, and 600 mmol (m2)−1 s−1. There was a significant effect of temperature and light intensity on survival, with less bacteria isolated from lettuce incubated at 25 and 18°C compared with 11°C (P < 0.0001), and in light intensities of 400 and 600 mmol (m2)−1 s−1 compared with 0 mmol (m2)−1 s−1 (P < 0.001). The average log reductions after 1, 2, 4, and 7 day(s) were 1.14, 1.71, 2.04, and 3.0, respectively. The QMRA compared the relative risk with lettuce consumption from 20 scenarios. A stricter water quality guideline gave a mean fivefold risk reduction. Holding times of 1, 2, 4, and 7 day(s) reduced the risk 3, 8, 8, and 18 times, respectively, compared with harvest the same day as the last irrigation. Finally, rinsing lettuce for 15 s in cold tap water prior to consumption gave a sixfold risk reduction compared with eating unrinsed lettuce. Sensitivity analyses indicated that variation in bacterial inactivation had the most significant effect on the risk outcome. A QMRA determining the relative risks between scenarios reduces uncertainty and can provide risk managers with decision support.

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