Health and safety in the Microbiology Department
The importances of health and safety principles in relation to the tests are taken in the Microbiology department. The role legislation in maintaining health and safety principles. Those who work in Microbiology laboratories are exposed to danger of infection from clinical specimens and laboratory cultures as well as to non-infective dangers such as cuts and other skin injuries, electric shocks, fire and explosion of gases and solvents, burning by corrosive chemicals, and acute and chronic poisoning from exposure to toxic substances.
In well regulated laboratories such incidents are rare, but constant attention is required to minimize their frequency. The nature of the risks must be well understood and careful precautions taken on a pre-planned and well organized basis. This understanding and the maintenance of good organisation and procedures is an essential component of the professional expertise of the laboratory worker in effect, simply part of a good technique.
Consideration must extend also of those in the general community who may be endangered by the ‘escape’ of infection, e.g. by careless disposal without prior disinfection or by the occurrence of infection in a laboratory worker who may transmit it to contacts outside the laboratory.
Immunity from previous natural exposure to infectious in the general community or resulting from vaccination gives useful protection against the corresponding pathogens when encountered during laboratory work. This does not justify a casual approach, however, since the immunity may not be complete; unexpected and unusual or exotic pathogens may be encountered in day-to-day work and it is wise to regard all human excretions, secretions, blood serum, tissues and derivatives thereof as potentially infectious.
Occurrence of Infections
It is difficult to assess how often infections are acquired during laboratory work because of the lack of the systematic collection and publication of information.
This has long been recognised as presenting a serious hazard to laboratory workers. In the recent British surveys 33 cases were reported in the 5 years 1979-83, the incidence rate being 43.8/100 000 person-years. The highest incidence was found in mortuary and post-mortem workers, both medical and other, and in Microbiology technicians. This finding is compatible with the main cause being aerosols generated during the work.
Hepatitis has also been prominent in reports over the years. In Britain, the incidence in laboratory workers fell markedly after 1974 and during the five years 1979-83 the survey related 23 cases, the incidence rate being
30.6/100 000 person-years. Of these, six hepatitis-A infections and one of infectious mononucleosis were attributed to exposure in the general community.
In most of these cases no accident leading to infection had been recognised, but the highest incidence rates were found in haematology, biochemistry and mortuary post-mortem workers, the high rate of infection being compatible with exposure to blood and infection by overt or inapparent parenteral routes.
The 1979-83 survey revealed 21 infections, all involving microbiology MLSOs except for one medical virologist who blamed a chicken meal. Accidental exposure in the laboratory was recorded in seven cases and suspected in several others, emphasizing the need for immaculate technique by microbiology bench workers for their own protection as well as to protect their work from cross-contamination. Ingestion is the likeliest route of infection in this group.
Many other laboratory-acquired infections have been reported over the years. In 1979-83 survey in Britain they included 12 cases of uncharacterized diarrhoea of uncertain significance. Streptococcal sepsis occurred in persons engaged in morbid anatomy and post-mortem examinations. Malaria was acquired by accidental needle-stick injury during collection of a blood sample. Brucellosis followed work on the open bench with blood cultures from an unsuspected case. Work with Coxiella burneti, rickettsiae, Chlamydia psittaci and Francisella tularensis has long been recognized to entail a high risk of accidental infection, but no such cases were reported in the 1979-83 British survey.
All occupations have their special hazards but although there are risks of infection in laboratory work with microorganisms, they are well recognized and can be contained by good laboratory practice. That this is so is shown by the very small number of infections acquired in recent years in clinical laboratories in relation to the large number of staff employed.
Routes of Infection
Literally, inoculation means the introduction of material into an ‘eye’ as in horticultural practice of grafting, and by analogy it covers the deliberate or accidental introduction of infection into the body, particularly by a breach of its surface. Thus, it covers the introduction of infection into the eye by splashing or by rubbing with contaminated fingers, injection through the skin by needle-stick injury or the bite of an ectoparasite, incision with a sharp instrument or broken glass, and injunction by the rubbing of material on to the skin or a mucous membrane. There are a few pathogens that can penetrate the skin or mucosa spontaneously, but usually the epithelia have small breaches of continuity that allow a wider range of microbes to reach the tissues.
Infection by the oral route may take place by the licking, sucking or accidental swallowing of infective material. It is especially liable to occur in the mouth-pipetting of cultures or other infected fluids. The cotton-wool plug in the upper end of a pipette does not protect against the risk and the finger placed at the upper end to control the pipette also touches the lips and may itself to contaminated. Infection may also be ingested after touching the mouth with contaminated fingers or writing instruments, or by licking labels contaminated by the fingers, or during eating, drinking or smoking in the laboratory.
Infection may take place by the breathing-in of an infected aerosol or dust. An aerosol is a cloud of small droplets of liquid in air. It usually contains many droplets smaller than 0.1 mm in diameter and these droplets dry rapidly to become solid residues, called ‘droplet nuclei’ so small, e.g. 1-20 um diameter, that they may remain air-borne for up to several hours.
Clouds of infective dust or spores can be released by the opening of containers of freeze-dried cultures or the withdrawal of cotton-wool plugs that have dried after being wetted by culture fluid. Convectional and other air currents can disperse aerosols and dusts widely within a laboratory and also into adjacent rooms. Particles larger than 5 um in diameter are mainly deposited in the nose and throat, whilst smaller particles can reach the bronchi and lungs.