Norovirus Outbreak Caused by a New Septic System in a Dolomite Aquifer

Abstract

Septic systems that are built in compliance with regulations are generally not expected to be the cause of groundwater borne disease outbreaks, especially in areas with thick vadose zones. However, this case study demonstrates that a disease outbreak can occur in such a setting and outlines the combination of epidemiological, microbiological, and hydrogeological methods used to confirm the source of the outbreak. In early June 2007, 229 patrons and employees of a new restaurant in northeastern Wisconsin were affected by acute gastroenteritis; 6 people were hospitalized. Epidemiological case‐control analysis indicated that drinking the restaurant's well water was associated with illness (odds ratio = 3.2, 95% confidence interval = 0.9 to 11.4, P = 0.06). Microbiological analysis (quantitative reverse transcription‐polymerase chain reaction) measured 50 genomic copies per liter of norovirus genogroup I in the well water. Nucleotide sequencing determined the genotype as GI.2 and further showed the identical virus was present in patrons' stool specimens and in the septic tank. Tracer tests using dyes injected at two points in the septic system showed that effluent was traveling from the tanks (through a leaking fitting) and infiltration field to the well in 6 and 15 d, respectively. The restaurant septic system and well (85‐m deep, in a fractured dolomite aquifer) both conformed to state building codes. The early arrival of dye in the well, which was 188 m from the septic field and located beneath a 35‐m thick vadose zone, demonstrates that in highly vulnerable hydrogeological settings, compliance with regulations may not provide adequate protection from fecal pathogens.

Domestic wells have high probability of pumping septic tank leachate

“…Moreover, regulations are typically developed based on very simple perceptions of groundwater flow; site-specific flow conditions are not accounted for (US EPA, 2002b). As Borchardt et al (2011) demonstrated in a case study, poor understanding of groundwater flow can lead to drinking water contamination, even if newly established septic systems are strictly built according to regulations. Few quantitative tools are available that would allow regulators, planners, or homeowners to assess the possibility of domestic wells pumping septic leachate-impacted groundwater (Wilcox et al, 2010).…”

“…Many studies demonstrated significant correlations of septic system density to contaminant concentrations and disease outbreaks (Schmidt, 1972;Pitt, 1974Pitt, , 1975Konikow et al, 1978;Katz et al, 1980;Duda and Cromartie, 1982;Bicki et al, 1985;Yates, 1985Yates, , 1991Hantzsche and Finnemore, 1992;Nizeyimana et al, 1996;Canter, 1997;Whitehead and Geary, 2000;Borchardt et al, 2011;Standley et al, 2008). In US EPA (1977), the agency specified a septic system density exceeding 40 systems per square mile (1 system per 16 acres) as at risk of groundwater contamination and considered septic system density to be the most important control of contamination risk from septic systems.…”

Environmental Transmission of Human Noroviruses in Shellfish Waters

“…Studies on contaminated groundwater suggest that NoV (GI) can remain detectable for over 3 years and infectious for at least 61 days (78). Therefore, poorly maintained septic tanks or leaking sewerage infrastructures could contaminate groundwater with fecal matter which could in turn contaminate surface waters through seepage (42). Surveillance of 23 groundwater wells in Korea showed that 18% of the samples were contaminated with NoV, with 71% of these being identified as GI and 29% as GII (79).…”

“…Significant quantities of NoV can be introduced into the marine environment from the discharges of municipal and private wastewater treatment works (39,40), from smaller-scale septic tanks (41,42), and from the overflows from such systems (43). Discharges may be directly introduced into shellfish waters or into watercourses higher in the catchment.…”

Leaching of Cryptosporidium parvum Oocysts, Escherichia coli, and a Salmonella enterica Serovar Typhimurium Bacteriophage through Intact Soil Cores following Surface Application and Injection of Slurry

“…Fertilization of agricultural land with livestock waste can lead to fecal contamination of waterways through surface water runoff, drainage systems, and groundwater if microorganisms are transported through the soil to groundwater reservoirs (23,53). Groundwater contamination by microorganisms of fecal origin has been reported over many years (1,77), and waterborne disease outbreaks have been associated with zoonotic pathogens like Cryptosporidium (29), Escherichia coli O157:H7, and Campylobacter (52,76), as well as norovirus (12). However, little documentation is available to what extent such contamination was caused by actual transport of pathogens through soil or fecal contamination through boreholes, intruding surface water, etc.…”