What are blood-borne viruses?
Blood-borne viruses (BBVs) are viruses that some people carry in their blood and can be spread from one person to another. Those infected with a BBV may show little or no symptoms of serious disease, but other infected people may be severely ill. You can become infected with a virus whether the person who infects you appears to be ill or not – indeed, they may be unaware they are ill as some persistent viral infections do not cause symptoms. An infected person can transmit (spread) blood-borne virsuses from one person to another by various routes and over a prolonged time period.
The most prevalent BBVs are:
- human immunodeficiency virus (HIV)- a virus which causes accuired immunodeficiency virus (AIDS), a disease affecting the body’s immune system;
- hepatitis B (HBV) and hepatitis C; BBVs causing hepatitis, a disease affecting the liver.
As well as through blood, these viruses can also be found and transmitted through other body fluids, for example:
- vaginal secretions;
- semen; and
- breast milk.
Unless contaminated with blood, minimal risk of BBV infection is carried by:
- vomit; and
The presence of blood in these bodily fluids and materials isn’t always obvious, so care should still always be taken to avoid infection.
Blood-borne viruses covered in this guidance
Pathogenesis of hepatitis B
Once inside the host, HBV is transported in the blood to the liver, where it infects liver cells. The incubation period of acute HBV infection is usually about 75 days, but can range from 45 to 200 days. The virus spreads in the liver and causes a spectrum of disease, ranging from acute hepatitis to chronic liver disease and liver tumours. A small proportion of patients with acute infection suffer liver failure, although most recover from the infection. Asymptomatic infection (infection without symptoms) and illness without jaundice does occur, particularly in children and the immunocompromised (those with an impaired immune system). The likelihood of a patient developing chronic infection is inversely related to age at the time of infection. Chronic infection occurs in at least 90% of infected neonates, 25% of children aged 1-5 years and 5% or less of adults. Chronically infected individuals are often referred to as HBV carriers.
HBV is an unusual virus as large quantities of viral proteins are produced, resulting in the production of a range of different particles, some of which are infectious and some of which are not. Viral proteins are secreted into the blood and their presence can be useful markers of infection. In individuals chronically infected with HBV, the persistence in the circulation of viral proteins indicates continuing high-potential infectivity for sexual partners and for babies born to carrier mothers. These chronically infected individuals, who may be totally without symptoms, also present a major risk to non-immune healthcare workersand others accidentally exposed to their blood and body fluids by, for instance, a needle-stick injury. In addition, the continued presence of viral proteins is associated with progressive liver damage (chronic active hepatitis and cirrhosis) and increased risk of primary liver cancer. Much of the damage to the liver in chronic cases is believed to be as a result of immune responses to the infection.
The severity of illness is clearly influenced by host immune responses to the virus. Antibody responses to HBV are induced by infection, and the specificity and type of these antibodies relative to levels of viral proteins is often indicative of the seriousness and nature of disease. The relationships between viral proteins, antibody generation and the progression of this disease are complex.
Pathogenesis of hepatitis C infection
Once inside the host, the HCV is transported in the blood to the liver, where it infects liver cells, although other types of cell, including blood cells, may also be infected. The incubation period for acute HCV infection is usually around 70 days, but can range from 2 to 26 weeks. The acute phase of HCV infection is often without symptoms, or mild. Diagnosis of infection is by detection of antibodies or virus RNA (ribonucleic acid) and/or antigen in serum. If the infection proceeds to a chronic phase, progression of liver damage is usually slow, and the most common complaint is fatigue. Liver enzyme abnormalities may fluctuate or persist, and the degree of liver damage is variable. The Department of Health estimates that between 60 to 80% of patients with acute HCV infection go on to develop chronic infection with a variable degree of hepatitis, with the risk of cirrhosis and, in a smaller number, primary liver cancer several decades later.
Transmission of hepatitis C
Routine screening of blood donors has been introduced to prevent transmission via transfusion and the use of blood products. The greatest risk of acquiring HCV in the UK is now through sharing of blood-contaminated needles and injecting equipment among drug users.
Routine screening of blood donors has been introduced to prevent transmission via transfusion and the use of blood products. The greatest risk of acquiring hepatitis C (HCV) in the UK is now through sharing of blood-contaminated needles and injecting equipment among drug users. Workplace exposure in the healthcare setting usually occurs as a result of a needle-stick or injury with other contaminated sharp instruments, and rates of occupational exposure and transmission are presented in HPA’s Eye of the Needle report. Exposure to other contaminated sharp injuries, for instance, via tattooing and skin piercing, may also result in infection. Mother-to-baby transmission o ccurs at a rate of about 3-5% (up to 15% in mothers who are also infected with human immunodeficiency viruses (HIV).
Prevalence of the hepatitis C virus (HCV) in the UK
HCV infection is a major worldwide public health problem, although the UK is thought to be a low prevalence area. Based on seroprevalent studies performed on residual specimens, the prevalence of HCV in England is predicted to be around 0.5-1%. As with HIV infection, the prevalence of HCV is often higher in major cities or other highly populated regions, compared to other parts of the UK, and is mostly associated with high-risk groups. This is demonstrated by the high incidence of hepatitis C among injecting drug users in Glasgow, London and the North West of England, (See – Shooting Up: Infections among injecting drug users in the UK, 2007 (updated 2008) ). Recent mathematical modelling data cited by the Health Protection Agency (HPA) indicates that, within England and Wales, 191 000 individuals had antibodies to hepatitis C virus. HPA also report 12 000 chronically infected individuals in Wales. In Scotland, (2006), around 50 000 people were estimated to be infected with hepatitis C; 38,000 with chronic infection. Estimates from Northern Ireland suggest that around 4000 individuals are likely to be chronically infected.
Most infections are due to injecting drug use. Since the discovery of HIV , there has been raised awareness of the transmission of blood-borne viruses through shared injecting equipment. However, a significant number of chronic infections may have been acquired in the 1970s and 1980s through contaminated blood products, before routine screening was introduced.
Approximately 80% of acute infections are without symptoms and 55-85% of all HCV infections become chronic. Therefore, it is likely that many infected individuals are unaware of their status. Some patients infected with HCV may also be infected with HIV or HBV (hepatitis B virus). Hepatitis C can now be treated. Around 50% of those who receive treatment clear the infection. As HCV infection is not always symptomatic, it is important that those at risk volunteer to be confidentially tested in order to benefit from such treatment. All blood donations are now tested for HCV. Again, the prevalence of HCV infection is likely to be higher in some areas and in some population groups, than in others.
Disposal of waste
BBV contaminated waste must be regarded as a hazardous substance, unless rendered safe before disposal. Most waste of this type, depending on its origin, will be classified as ‘clinical or infectious waste’ and is subject to stringent controls.
The principles of waste segregation and its secure storage are applicable in most occupational settings where any significant amount of waste is generated. This will include material generated in, for example, the care of patients in the community. Waste of this nature is most likely to fall into Category B infectious waste, requiring labelling as UN3291 and packaging in bags/wheelie bins as per packaging instruction P650. Detailed guidance on management and handling of infectious healthcare waste is provided by Department of Health (HTM) 07-01.