More than 500 patients were invited to attend special blood-screening clinics at Royal Sussex County Hospital because they might have been exposed to the hepatitis C virus.

A worker at the hospital was discovered to be carrying the virus after undergoing a routine blood test.

The actual risk of a patient being infected is minimal - less than one per cent - but the tests were made available to those patients who were worried.

Hepatitis means inflammation of the liver. The most common cause is infection with a virus but it can also be due to drinking too much alcohol or be a side effect of some drugs.

There are several different viruses that affect the liver, primarily hepatitis A, B, C, D and E. The main difference between them is the way they are spread, the damage they cause to the liver and the effects they can have on general health.

Hepatitis C is passed on through several methods. The first is by contact with blood. A tiny amount of blood - too small to be visible to the naked eye - from someone who has the virus, will transmit the infection if it gets into someone else's bloodstream through, for example, an open wound, cut or scratch.

All newly-qualified NHS workers are screened for hepatitis C but it is not done routinely as the risk of infection is so small.

However, regular checks for the B strain are carried out as this is more infectious.

Sexual transmission of hepatitis C is thought to be unusual but does occur occasionally.

Doctors are unsure whether infections between partners is because of sexual exposure or because of other reasons, for example, sharing a personal item such as a toothbrush or razor.

People with more than one sexual partner are advised to use condoms as there is some evidence those with many sexual partners have an increased risk of being infected.

Condoms may reduce the risk of infection.

Infection is not acquired through normal social contact, for example, from a cup or by touching an infected person.

Recent research has found between 50 and 80 per cent of past and present drug users may be infected with hepatitis C. They become so by sharing contaminated equipment.

An increasing number who injected years ago are only now being diagnosed as having hepatitis C.

Other ways of contracting the infection are through acupuncture, tattoos and body piercing. Such cases are rare and usually caused by the use of unsterile needles.

People planning to get their ears or other parts of the body pierced should ensure disposable needles are used and that they come straight out of a sterile packet.

Hepatitis C has only been recognised since 1989 and it is only recently that tests to diagnose the virus have become available.

Doctors believe transmission rates in the general population for hepatitis C are low and the incubation period is between two weeks and six months.

Many people who are infected do not realise they have the infection and suffer no symptoms at all, while others have a mild infection or nausea and suffer some abdominal pain and jaundice.

Thousands of people have been diagnosed in the UK but the true figure is believed to be much higher.

One in five people with hepatitis C recovers completely.

Some of those infected can become carriers and have an increased lifetime risk of liver disease.

Heather Phillips, an public health expert from Chichester, said: "There is a lot of work that needs to be done to get people with the disease diagnosed and treated.

"The risk of infection is small when it comes to such incidents as the worker at the Brighton hospital but there are other ways it can be caught so it is important people are aware of the potential risk."

Hepatitis B, sometimes called Hep B or HBV, is more prevalent but can be prevented by vaccination. It is common in south-east Asia, the Middle and Far East, southern Europe and Africa.

More details about all the strains of hepatitis are available from the British Liver Trust web site