Infectivity of Norovirus GI and GII from Bottled Mineral Water during a Waterborne Outbreak, Spain

During a waterborne outbreak of norovirus in Spain, we estimated 50% illness doses for a group of exposed (secretor) persons to be 556 (95% CI 319-957) genome copies/day for norovirus GI and 2,934 (95% CI 1,683-5,044) genome copies/day for norovirus GII. Use of a propidium monoazide viability assay reduced these values. Human noroviruses are a major agent of acute gastroenteritis, are distributed worldwide, and affect all age groups (1). One of the largest outbreaks of infection with norovirus, caused by consumption of contaminated bottled spring water, occurred in Spain during 2016 and affected >4,100 persons (2). Multiple genotypes (GI.2, GII.2, GII.4, and GII.17) were identified among patients, and high levels of norovirus genomes were quantified in contaminated water coolers.