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To determine inactivation profiles of three human norovirus (NoV) surrogate viruses and coliphage MS2 by ultraviolet (UV) irradiation and the protective effect of cell association on UV inactivation.The inactivation rate for cell-free virus or intracellular echovirus 12 was determined by exposure to 254-nm UV light at fluence up to 100 mJ cm−2. The infectivity of murine norovirus (MNV), feline calicivirus (FCV) and echovirus 12 was determined by cell culture infectivity in susceptible host cell lines, and MS2 infectivity was plaque assayed on Escherichia coli host cells. The UV fluencies to achieve 4-log10 inactivation were 25, 29, 30 and 70 (mJ cm−2) for cell-free FCV, MNV, echovirus 12 and MS2, respectively. However, a UV fluence of 85 mJ cm−2 was needed to inactivate intracellular echovirus 12 by 4 log10.Murine norovirus and echoviruses 12 are more conservative surrogates than FCV to predict the UV inactivation response of human NoV. Intracellular echovirus 12 was 2·8-fold more resistant to UV irradiation than cell-free one.Variation in UV susceptibilities among NoV surrogate viruses and a likely protective effect of cell association on virus susceptibility to UV irradiation should be considered for effective control of human NoV in water.