Passengers travelling on the NorthLink ferry Hjaltland are being warned of a sickness and diarrhoea bug onboard the vessel.
Eighteen members of crew became ill over the festive period – though not at the same time – prompting the ferry operator to offer passengers the chance to cancel their bookings or transfer to another service.
Another crew member has since begun to suffer from the same symptoms.
NorthLink says no passenger has so far declined to travel, and hundreds have sailed since the illness came to light.
Crew members affected have been confined to their cabins for the duration of their illness, which has usually passed within 24 hours.
No sailings have been cancelled as a result of the illness, however the vessel has been subject to a complete “deep clean regime”, following advice from environmental health.
NorthLink say letters warning of the illness would continue to be issued until the bug had completely gone away.