Introduction

Blood-borne viruses (BBVs) include HBV, HCV and HIV, though this is not an exclusive list of organisms found in blood that are transferable by direct inoculation, nor is blood the only potentially hazardous material.  Good laboratory practice surrounding the handling of body fluids potentially infected with BBVs is, however, generically protective.

Risks

•  ALL body fluids can be infected with BBVs and should be handled with the same precautions as blood.

• In the context of a laboratory, sharps injuries carry the greatest risk but splash contamination to mucous membranes is also hazardous.

• Patients with BBVs are often not diagnosed until some time after admission to hospital, eg diagnosis of HIV takes, on average, 10 days.

• As a rough guide, approximately 1% of specimens received in the laboratories are likely to contain one of the BBVs.  On an average day, this would be 25 to 30 specimens.

•  In the majority of samples the risk is likely to be unknown. 

'It’s the train you don’t see that kills you, not the one you do see'.

Laboratories must rely on good laboratory practice in the handling of all specimens if risks are to be minimised.

The risks associated with the individual viruses carry different levels of risk, not only because of relative infectivity, but also the availability of immunisation or prophylactic treatment.

HIV
Currently there are approximately 50,000 known HIV positive people in the UK; the true level is conservatively twice this number.  In parts of the world (Central Africa) seroprevalence exceeds 20%.  Almost all patients that are HIV antibody positive are potentially infectious.  From direct inoculation by needle stick injury from a know positive, seroconversion occurs in 3:1,000.  Splash injury to mucous membranes carries an estimated risk of 1:1,000.  Chemoprophylaxis is available following high-risk injury. 

HCV
The UK prevalence of HCV is of the order of 0.1-0.4% of the population.  High-risk groups, eg IVDA, may have carriage rates of the order of 70-90%.  Approximately 80% of antibody patients can be deemed infectious.  The major long-term risks of HCV are chronic liver diseases.

Treatment is available but is unpleasant and only “cures” about 50% of infected individuals. 

HBV
Seroprevalence of HBsAg in the UK is approximately 0.2% but prevalence rates of 10-20% are well recognised in tropical and subtropical areas.  Only about 5% of those patients developing HBV will become carriers.  Transmissibility is heavily dependent upon the profile of HBV markers.

Immunisation is the most reliable way of preventing disease.  Treatment is available, but cure rates are relatively low.

General Measures

In accepting a system of universal precautions, it is necessary to carry out a risk assessment.  This involves establishing the step-by-step process of a specimen from patient to disposal, evaluating the risks at each step and taking measures to minimise risks.  Examples might include venepuncture and the safe disposal of sharps, protocol for safe handling of leaking specimens, centrifuge accidents, etc.

Irrespective of the risk assessment, there are a number of mandatory precautions that must be practised:

• Hand washing must be performed whenever contamination may have taken place and when leaving the laboratory areas. 

• Gloves and other protective clothing must be worn when handling blood, blood products or other clinical material. 

• All samples requiring centrifugation should be centrifuged in sealed capped buckets.

• Wounds and any skin lesions must be covered with waterproof dressings. 

• Disposal of specimens must be in accordance with departmental protocols.

• Safe handling and disposal of sharps must be undertaken.

• All staff should undergo Occupational Health Department screening and be appropriately immunised.

• Any accidents must be reported.  In the event of exposure to BBVs, the Occupational Health Department should be consulted.

This is not an exhaustive list – it is intended to illustrate a code of good practice.

Dr. R.J. Sage -December 2003