More than 4,000 people in England may need a liver transplant by 2020 because of hepatitis C, experts have warned.
Data from the Health Protection Agency (HPA) suggests around 4,200 people could need a transplant owing to serious damage to their liver, with many unaware they have the condition at present.
Experts estimate around 216,000 people in the UK are living with chronic hepatitis C, many of whom are currently undiagnosed. People can catch the disease through contact with the blood - and less commonly the bodily fluids - of an infected person.
Those who share needles and use unsterile drugs equipment are particularly at risk, although people who had a blood transfusion before 1991 or received blood products before 1986 have a higher chance, as well as those having treatments abroad. Sharing toothbrushes, razors and scissors also heightens the risk, as does having tattoos.
Dr Helen Harris, hepatitis expert at the HPA, said: "Many people are unaware that they are infected with the virus because they have no symptoms at all. If people think they have been exposed to the virus, it is vital that they contact their GP for a test. The earlier they are diagnosed the better, as they will have a greater chance of successfully treating their infection."
The report said 15,000 people in England could be living with cirrhosis of the liver or liver cancer caused by hepatitis C in 2020 unless they are diagnosed and treated.
Drug treatments can successfully clear the virus in more than half of those infected. In 2010, 7,834 new diagnoses of hepatitis C were reported to the HPA in England.
A Department of Health spokesman said: "More people are being tested for hepatitis C, leading to more people getting the right treatment. Treatment successfully clears the virus in more than half of all cases, and there are newer, more effective treatments being developed.
"But there are many people who don't know they have hepatitis C as it doesn't usually cause symptoms for many years - it could be someone who injected drugs once 30 years ago, or someone who got a piercing with an unsterilised needle.
"World Hepatitis Day is a timely reminder that if in doubt, get checked out. Anyone who wants more information about hepatitis C should talk to their GP or visit NHS Choices."