The Aurora was at the centre of an outbreak of the Norovirus in 2003
Hundreds of holidaymakers are being tested for Hepatitis E after an outbreak onboard P&O liner Aurora.
Seven passengers contracted the virus during an 11-week world cruise which ended in Southampton on 28 March.
All the passengers onboard were sent a letter from the Health Protection Agency requesting a blood sample.
The HPA advises that the virus, which affects the liver, can be fatal but only in rare cases. P&O said it was cooperating fully with the inquiry.
It is thought the passengers caught the virus through eating or drinking contaminated food.
The HPA said about 1,100 passengers volunteered to be screened but only a sample of 600 - who provided blood samples in the time frame - will be sent a questionnaire asking them what they ate and drank on board and ashore.
The questionnaire also requested a blood sample if they had been exposed to the virus.
In a statement it said: "Seven cases of Hepatitis E have been confirmed amongst passengers on the Aurora world cruise who travelled between 7 January and 28 March 2008.
"The agency has been coordinating a study of the incident, by inviting passengers from the cruise to answer a questionnaire and provide a small sample of blood to test.
"The cruise has visited many locations including countries in which Hepatitis E is endemic.
"The illness was most likely contracted by eating or drinking contaminated food or water during the cruise. Person-to-person transmission is very uncommon and unlikely.
"The ship has rigorous public health procedures and underwent a formal public health inspection recently in which it scored very highly."
A spokeswomen for P&O said: "We have been working closely with the Health Protection Agency and will continue to assist in the inquiry."
Symptoms of the illness, which is a severe form of liver inflammation, include yellowing of the skin and eyes (jaundice) and darkening of the urine.
It can take up to 60 days to appear in patients and takes up to four weeks to clear.
The £200m Aurora liner has a history of problems ever since the bottle of champagne failed to smash when Princess Anne named her in 2000.
In 2003, 600 passengers and crew caught the vomiting bug Norovirus and two years later the ship spent 11 days circling the Isle of Wight while an engine problem was repaired before the round the world cruise was abandoned.