Quantitative microbial risk assessments (QMRAs) often lack data on water quality leading to great uncertainty in the QMRA because of the many assumptions. The quantity of waste water contamination was estimated and included in a QMRA on an extreme rain event leading to combined sewer overflow (CSO) to bathing water where an ironman competition later took place. Two dynamic models, (1) a drainage model and (2) a 3D hydrodynamic model, estimated the dilution of waste water from source to recipient. The drainage model estimated that 2.6% of waste water was left in the system before CSO and the hydrodynamic model estimated that 4.8% of the recipient bathing water came from the CSO, so on average there was 0.13% of waste water in the bathing water during the ironman competition. The total estimated incidence rate from a conservative estimate of the pathogenic load of five reference pathogens was 42%, comparable to 55% in an epidemiological study of the case. The combination of applying dynamic models and exposure data led to an improved QMRA that included an estimate of the dilution factor. This approach has not been described previously.
Journal of Water and Health, 2013, Vol 11, Issue 4, p. 636-646
ENVIRONMENTAL; MICROBIOLOGY; ESCHERICHIA-COLI O157; WASTE-WATER; CRYPTOSPORIDIUM OOCYSTS; ENTERIC VIRUSES; DOSE-RESPONSE; GIARDIA CYSTS; GASTROINTESTINAL ILLNESS; RECREATIONAL WATERS; TREATMENT-PLANT; SURFACE-WATER; combined sewer overflow; dilution factor; extreme rain event; hydrodynamic modelling of bathing water quality; hydrodynamic modelling of sewers; quantitative microbial risk assessment; Copenhagen Denmark, Europe Palearctic region; contaminated bathing water; ironman competition; rain event; total estimated incidence rate; waste water contamination; Eubacteria Bacteria Microorganisms (Bacteria, Eubacteria, Microorganisms) - Aerobic Helical or Vibrioid Gram-Negatives  Campylobacter jejuni species pathogen; Facultatively Anaerobic Gram-Negative Rods Eubacteria Bacteria Microorganisms (Bacteria, Eubacteria, Microorganisms) - Enterobacteriaceae  Escherichia coli species pathogen; Positive Sense ssRNA Viruses Viruses Microorganisms (Microorganisms, Positive Sense Single-Stranded RNA Viruses, Viruses) - Caliciviridae  Norovirus genus pathogen; Primates Mammalia Vertebrata Chordata Animalia (Animals, Chordates, Humans, Mammals, Primates, Vertebrates) - Hominidae  human common adult female, male; Protozoa Invertebrata Animalia (Animals, Invertebrates, Microorganisms, Protozoans) - Flagellata  Giardia genus; Protozoa Invertebrata Animalia (Animals, Invertebrates, Microorganisms, Protozoans) - Sporozoa  Cryptosporidium genus; 04500, Mathematical biology and statistical methods; 10515, Biophysics - Biocybernetics; 31000, Physiology and biochemistry of bacteria; 33502, Virology - General and methods; 36006, Medical and clinical microbiology - Virology; 37014, Public health - Sewage disposal and sanitary measures; 64002, Invertebrata: comparative, experimental morphology, physiology and pathology - Protozoa; Computational Biology; Sanitation; drainage model mathematical and computer techniques; three-dimensional hydrodynamic model mathematical and computer techniques; Infection; Models and Simulations; Waste Management; Bathing Beaches; Denmark; Environmental Monitoring; Gastrointestinal Diseases; Humans; Rain; Risk Assessment; Sewage; Sports; Time Factors; Water Microbiology; Water Pollution