Volume 6: Human Health, 1989-96
8. Development of guidance on occupational risks from BSE and other TSEs
Early 1980s
Guidance on TSEs before the emergence of BSE
The categorisation of pathogens

Guidance on TSEs before the emergence of BSE

8.20 The potential risks of cross-infection for health workers caring for, or working with tissues from, patients with TSEs or other dementias were recognised in the late 1970s. In 1979 the CMOs (Chief Medical Officers) in England, Scotland and Wales set up the Advisory Group on the Management of Patients with Spongiform Encephalopathy (Creutzfeldt-Jakob Disease (CJD)). It had the following terms of reference:

To consider in the light of available evidence what measures need to be taken by persons caring for and carrying out clinical and laboratory procedures, including post-mortem examinations on patients with transmissible spongiform encephalopathy or other dementias, in order to avoid any potential hazard from cross-infection by these agents from patients or their tissues. ¹

8.21 In November 1981 the Advisory Group produced guidance on precautions to be observed when caring for patients suffering from CJD or handling their tissues. ² The Group decided to confine its recommendations to CJD, which at that time:

[was] the only known transmissible form of spongiform encephalopathy likely to be encountered in Europe. ³

8.22 The report noted the occurrence of iatrogenic patient-to-patient transmission of CJD in three cases following neurosurgery and in one following transplantation of a corneal graft donated by an affected patient. It also noted a further three patients 'who had all had neurosurgical procedures in one hospital in the same year, subsequently contracted CJD. It is possible that these cases arose as a result of cross infection.' ⁴

8.23 The report recommended a number of precautions to be taken when attending patients with known or presumed CJD. The objective was to reduce the risk of contamination from various procedures involving tissues, blood and other body fluids. The recommended precautions were directed at the following: transplant and tissue donations, ward procedures, theatre procedures, transmission of specimens, precautions in the laboratory, post-mortem examination and accidental contamination. An appendix to the guidance set out the recommended sterilisation procedures for surgical instruments. ⁵ The guidance in relation to these sterilisation procedures was updated in 1984. ⁶

The categorisation of pathogens

8.24 In 1984 ACDP, an advisory Committee to HSC, produced the first edition of 'Categorisation of Pathogens'. This categorised infectious agents into four numbered Hazard Groups (1-4) and set out four levels of containment for microbiology laboratory activities and work with infected animals. The publication was updated in 1990. ⁷

8.25 Hazard Group 1 organisms are those most unlikely to cause human disease, whereas Group 4 organisms are those that cause severe human disease, presenting a serious hazard to laboratory workers as well as a high risk of spread to the community, and for which there is no effective treatment. The following table shows ACDP's definition of the Hazard Groups and examples of recommended containment measures for each Group:

Table 8.1: Definition of Hazard Groups 

Hazard Group	Definition	Examples of recommended containment
1
Laboratory personnel must receive instruction in the procedures conducted in the laboratory	An organism that is most unlikely to cause human disease	The laboratory should: be easy to clean, maintain an inward air-flow and contain adequate hand washing facilities. Workers in the laboratory should: close doors when working, wear appropriate gowns, etc, not eat, chew, drink, smoke or apply cosmetics, not practise mouth pipetting, disinfect hands after handling viable materials, minimise the production of aerosols, clean bench tops, store laboratory glassware and other materials in a safe manner, render waste material as non-viable before disposal. Waste material: should be transported in robust containers without spillage.
2
Laboratory personnel must receive instruction and training in handling pathogens, and an appropriate standard of supervision of the work must be maintained	An organism that may cause human disease and which might be a hazard to laboratory workers but is unlikely to spread to the community. Laboratory exposure rarely produces infection and effective prophylaxis or effective treatment is usually available.	The laboratory should: be easy to clean, maintain an inward air-flow, contain adequate hand-washing facilities near the exit, have limited access (to laboratory personnel and other specified persons), provide adequate space for each person (24m3) and have effective disinfectants available for routine disinfection. Workers in the laboratory should: close doors when working, wear side or back fastening gowns, not eat, chew, drink, smoke or apply cosmetics, not practice mouth pipetting, disinfect hands after handling viable materials, generally work on the open bench and minimise the production of aerosols, use a microbiological safety cabinet when shaking vigorously, mixing or using ultrasonic disruption etc, disinfect bench tops, store laboratory glassware and other materials in a safe manner, render waste material safe before incineration. Waste material: should be transported in robust containers without spillage.
3
Laboratory personnel must have had training in handling pathogenic and potentially lethal organisms and in the use of safety equipment and controls. A high standard of supervision of the work must be maintained	An organism that may cause severe human disease and presents a serious hazard to laboratory workers. It may present a high risk of spread to the community but there is usually effective prophylaxis or treatment available	The laboratory should: be easy to clean, be sealable to permit fumigation, sited away from general circulation and provide adequate space for each person (24m3), have access limited to authorised personnel, have its door locked when unoccupied and have a door with a glass panel so that occupants can be seen, have a biohazard sign posted at entry, have a continuous airflow into the laboratory and contain its own equipment so that all Hazard 3 materials are held within the laboratory and nowhere else. Workers in the laboratory should: close doors when working, wear side- or back-fastening gowns, not eat, chew, drink, smoke or apply cosmetics, not practise mouth pipetting, wear gloves for all work with infective materials, wash hands before leaving the laboratory and make all waste materials safe before disposal or incineration. Waste material: should be transported in robust containers without spillage.
4
A specific code of practice must be prepared for the work in the laboratory and a safety officer must be appointed and be accountable to the person identified as responsible for the work. Personnel must be over the age of 18 and must have had specific training in the working of the laboratory, and the use of safety equipment and must receive specific training, instruction and information on the handling of the pathogen(s) concerned. The work must be supervised.	An organism that causes severe human disease and is a serious hazard to laboratory workers. It may present a high risk of spread to the community and there is usually no effective prophylaxis or treatment.	The laboratory should: be easy to clean, be sealable to permit fumigation, sited in an isolated part of the building and access be limited to authorised personnel, provide adequate space for each person (24m3), have entry through an airlock with the outer door labelled with a 'work in progress' sign, include an observation window, etc, so that occupants can be seen, provide a telephone or other means of outside communication, have effective disinfectants available for immediate use, have an efficient insect and rodent control programme and provide high-performance respiratory protective equipment for use in an emergency. Workers in the laboratory should: be accompanied by at least one other competent person to assist in case of an emergency, wear a complete change of clothing in the laboratory unit and shower before leaving, not eat, chew, drink, smoke or apply cosmetics, not practise mouth pipetting, conduct all laboratory procedures with infective materials in a Class III microbiological safety cabinet, store all infective material in the laboratory unit and nowhere else, make all material safe before removal (which must be conducted by a safety officer) from the laboratory. Waste material: should be transported in robust containers without spillage.