It’s one of the enduring mysteries of cruise – how do sanatised ships still become contaminated by norovirus?

A new US study, published in Royal Society Open Science, underscored what we already know: not much can be done, once the disease takes hold.

But a computer-based model of a norovirus outbreak on a cruise ship designed to work out the likely suspects in this medial who-dunnit points the finger at the crew.

The scientists studied about 2,400 passengers and 999 crew members during a six-week period.

During the six-week period, weekly cruises took place, with new passengers at each cruise, but with crew members remaining the same.

According to research, the first two cruises recorded the largest number of acute gastroenteritis (AG) cases, caused by a single strain of norovirus.

The ship was sanitised between onboarding new passengers, however the AG cases continued on subsequent cruises, although at a decreased level and caused by several strains of norovirus instead of the original, single strain.

The researchers concluded that the initial AG outbreak may have been due to potential food contamination (since the strain was the same), but the secondary cases were likely due to person-to-person infection, with the crew potentially spreading the bug from cruise to cruise despite the hygiene measures undertaken between the embarkations.

The study found that environmental cleaning and isolating ill passengers appeared to have little impact, concluding that personal hygiene measures such as hand washing were the most effective in preventing the spread of illness.