British Liver Trust

Globally, the major mode of HBV infection is perinatal transmission although patterns of transmission are shifting due to the introduction of universal vaccination programmes in many countries.

In countries with low endemicity the spread is caused predominantly by sharing contaminated equipment during injecting drug use and through sexual contact.

In the UK, the most reported risk factor, for new cases among adults with a known likely source of infection, is injecting drug use followed by sexual contact. Many patients, perhaps up to one third, will not know how they acquired the infection.

Hepatitis B is not spread by casual contact such as touching hands and kissing, or sharing towels and eating-utensils. Faeces of chronic HBsAg carriers do not appear to harbour the virus.

Exposure to blood
The source of most HBV infection is probably exposure to blood and secretions from chronic carriers.

Highest amounts of HBV are present in blood. HBsAg carriers vary considerably in their infectivity from less than 10 to greater than 10⁸ virions/ml of plasma.

Patients with HBeAg (Hepatitis B e-antigen) in addition to HBsAg generally have more than 10⁶ virions/ml in serum, which explains why transmission of hepatitis B usually occurs from exposure to an HBeAg-positive person.

The introduction of HBsAg screening of blood donations in the UK and viral inactivation of blood products has all but eliminated these as a source of infection in this country.

Drug paraphernalia is often shared and is thus at risk of being HBVcontaminated.

This includes not only needles but also barrels, filters, spoons, citric or water. The virus is able to persist in dried blood on implements and surfaces for at least one week. Tattooing, body-piercing and acupuncture may also pose a risk if unsterilised equipment is used.

Patients should always avoid sharing needles and syringes, razors and shaving equipment, and toothbrushes.

Other body fluids
HBsAg can also be detected in other bodily secretions such as saliva, semen and vaginal fluid, even without blood contamination. However, the amount of virus is always 100 to 1000-fold less than in blood.

While HBsAg can occasionally be found in urine, breast milk, cerebrospinal fluid, sweat, tears and bile, the amounts are low and have not proved infectious.

Sexual transmission
The virus can be spread by sexual contact. Transmission usually occurs through exposure of mucous membranes to infected blood or body fluids during vaginal or anal intercourse.

Young adults engaging in high-risk sexual behaviours such as unprotected sex (penetrative or oral) and with multiple partners are at greatest risk of infection.

Perinatal transmission
Maternal to infant spread is an important means by which the virus is sustained in worldwide populations. This has been reduced by the universal infant vaccination programmes recommended by the WHO. In 1992 just 31 countries vaccinated infants against hepatitis B during national immunisation programmes. By 2007 this had increased dramatically to 171 countries.

In the UK, the Joint Committee on Vaccination and Immunisation (JCVI) recommends targeted rather than universal infant vaccination. Pregnant women are offered antenatal screening for hepatitis B infection and babies born to infected mothers are immunised at birth. Infants of mothers who are known to be very infectious from antenatal screening are offered both hepatitis B immunoglobulin and immunisation. The cost effectiveness of universal immunisation of infants or teenagers is currently being re-assessed as part of the continual review of immunisation policy in the UK.

Although breast milk of HBsAg positive mothers has been found to be positive for the virus, there have not been any reports of HBV transmission through breast-feeding, even before the availability of hepatitis B vaccine for infants. Any residual risk of transmission would be almost completely abolished by ensuring that the infant is vaccinated on time. Mothers who breast-feed are advised to take good care of their nipples to avoid cracking and bleeding which may increase the risk of other unrelated problems.

Clinicians should promote the importance of timely vaccination and discuss the risks and benefits of breast-feeding to reassure pregnant women.

The acute phase of the infection in children and newborns is typically mild and not associated with apparent illness. However, infection during the neonatal period almost always leads to chronic infection.

Interfamilial transmission
Non-sexual interfamilial spread is not commonplace but may occur. It becomes common when the first family member to be infected is an infant or child and is seen most clearly amongst adoptive parents of chronic HBsAg carrier children.

Travel
Travel to endemic regions accounts for around 12% of cases in the UK.

The risk to travellers to high or intermediate prevalence areas is increased with certain activities such as high risk sexual activity, injecting drug use, medical or dental procedures, undertaking relief aid work and/or participating in contact sports.

Around a half of travel-related cases in England, Wales and Northern Ireland reported heterosexual exposure as a risk factor.

Individuals likely to need medical or dental treatment should be vaccinated before they travel; these include those remaining for lengthy periods, children or others who may need medical care while visiting families or relatives, those with chronic medical conditions and those travelling for medical care. It is particularly important to ensure that individuals who may require dialysis are aware of the risks of blood-borne virus acquisition whilst overseas and are fully vaccinated and the response to vaccination documented.

Occupational risks
Hepatitis B is an important occupational hazard for healthcare workers via accidental needle sticks, injury from sharp objects, or direct exposure to blood and body fluids to breaks in the skin or to mucous membranes (eyes, inside of the mouth and nose). This risk can be virtually eliminated by preexposure vaccination of individuals at risk of needlestick accidents and by appropriate post-exposure risk assessment and management of those not fully protected.

Similarly an infected health care worker may present a risk to patients.

It is vital that healthcare workers are vaccinated and, if injured at work with sharp objects or needles, have appropriate tests and follow-up checks for hepatitis. Without this there is also the unnecessary risk of developing chronic infections, hepatitis B, C or HIV.

Other professions may also be at risk due to exposure to blood or body fluids, such as laboratory staff, staff in accommodation caring for those with learning difficulties, the prison service, police, social work, parks and funeral workers. Vaccination is recommended for anyone at occupational risk and it is a requirement for the employer to ensure that the risk to staff is assessed and all reasonable measures taken to reduce this risk, including providing vaccination.