Norovirus human infectivity and persistence in groundwater

Norovirus (NoV) gastroenteritis outbreaks are associated with contaminated groundwater, surface water, and recreational water and cause serious morbidity and economic losses. To better understand the mechanisms and risks of waterborne NoV transmission, we examined how long NoV remains infectious in water. A 10% solution of Norwalk virus (NV) inoculum (8FIIb) was added to groundwater and stored in the dark at room temperature. NV RNA was quantified by real-time reverse transcription-PCR in aliquots stored for 0, 7, 14, 21, 35, 70, 411, 440 and 620 days. However, levels of NoV RNA in water may not be correlated with risk of infection. Therefore, we seeded samples of groundwater that met EPA drinking water standards with high doses (1 x 10^7 genomic copies) of safety-tested NV inoculum (8FIIb). After admission into a clinical research unit, we challenged 13 genetically-susceptible, adult volunteers with this seeded water that was stored at room temperature in the dark for 0, 7, 14, 21, 27, or 61 days. Infection status was determined by the presence of NV RNA in stool or by a ≥4-fold increase in NV-specific serum IgG. NV RNA was detected in the seeded groundwater for over 620 days. Ten of 13 volunteers became infected with NV, including 2/2 volunteers who ingested seeded water at 61 days. Our data show that NoV RNA is detectable in groundwater for over 1.5 years. NoV remained infectious in groundwater for at least two months and can pose a serious risk in untreated, contaminated groundwater.