Purpose: We aimed to determine the norovirus bioburden on highly touched surfaces, on six cruise ships, during norovirus outbreaks and to assess the disinfection efficiency of several disinfection procedures.
Methods: Swab samples were collected from highly touched surfaces (n=95) in 19 AGE case cabins, as well as from surfaces (n=110) in public areas on the disembarkation day of six cruise ship voyages. After cleaning and room disinfection, the same surfaces in 16 case cabins were again sampled to determine norovirus reduction. Norovirus RNA was extracted using lysis buffer and concentrated using spin columns. RNA preparation was followed by realtime RT-PCR assays for detection and quantification of norovirus titers.
Results: Norovirus was detected in 43 (45.3%) of the 95 swab samples from case cabins and from 30 (27.3%) of the 110 samples from public areas. Viral titers ranged from 1.2 to 7.4 log RNA copies for the case cabin samples and from 1.6 to 2.7 log RNA copies for the public areas. Toilet seats in cabins showed the highest norovirus contamination rates 67% (12 of 19) with a titer range of 4.3 to 6.8 log RNA copies. Average norovirus reduction titers, on cabin surfaces after disinfection, was 0.4 log. Different disinfection measured on the ships resulted in a modest reduction of norovirus RNA levels (≤1.6 log). There were no illnesses reported in those cabins on the subsequent voyage.
Significance: This is the first study to characterize the level of environmental contamination on cruise ships during norovirus outbreaks. Overall, our data help to explore a framework for evidence-based norovirus outbreak management on cruise ships.