Purpose: Determine norovirus contamination on environmental surfaces on a cruise ship
Methods: During a 5-day voyage of cruise ship A, several suspected cases of norovirus illness were reported. Within 2 hours after disembarkation of the passengers, environmental swab samples were collected from hard surfaces of several cabins from ill passengers as well as from surfaces in public places. Samples were shipped overnight on dry-ice and stored frozen until processing. Virus was eluted from the swabs and extracted using a newly developed norovirus extraction protocol. Extracts were tested for GI/GII norovirus by multiplex real time RT-PCR assay with coliphage MS2 included as a process control.
Results: A total of 92 swab samples were collected of which 17 (18%) tested positive for GII norovirus. Samples of 3 of the 6 cabins of symptomatic passengers tested positive including 50% of the restrooms. The norovirus load in the samples ranged from 16 - 31,217 RNA copy numbers. Overall, the viral load in the samples from the cabins (range 80 to 31,217) was higher than in the samples collected from the public spaces (range 16 to 113 RNA copy numbers). Four (23.5%) of positive swab samples could be sequenced and had identical sequences which could be genotyped as GII.1.
Significance: The viral load of the positive swab samples correlated with the location of known symptomatic norovirus passengers on the ship. Focusing environmental sampling on restrooms as index locations may provide a sensitive monitoring tool to identify norovirus contamination in high-risk settings to help guiding strategies to control norovirus.