Part I: Organisation and management
laboratory worker health monitoring

Transmission of tuberculosis - including multidrug-resistant tuberculosis - is a recognised risk for laboratory workers, while infection with HIV facilitates transmission of tuberculosis. Most people do not develop tuberculosis disease following infection, since specific cell-mediated immunity usually develops within a few weeks after the initial infection. In immuno-competent persons, this immunity arrests multiplication of bacilli and averts clinical disease. HIV, however, kills T-helper cells (T4 lymphocytes) which reduces an infected individual defence against M. tuberculosis. HIV infection therefore increases the risk of reactivation of dormant tuberculosis infection, as well as the risk of progressive disease following new infection.

For the establishment of a tuberculosis infection sufficient to produce disease, exposure must be close and prolonged, the environment laden with infectious droplet nuclei and the prospective host unprotected by his/her own immune mechanisms, as indicated in Figure 2. All of these may be present in tuberculosis laboratories: Poor laboratory hygiene and disregard of safety measures increase the ease of transmission of infection, while factor adversely affecting the immune status of individuals (eg. HIV, diabetes, cancer, alcohol abuse) increase the development of disease.

Figure: Probability of developing tuberculosis following infection: Influence of the number of infecting bacilli, the duration of exposure and the competence of an individual's simmune system.
(Acknowledgement: Crofton J., Horne N., Miller F. - Clinical Tuberculosis, Butterworths, Londorn, 1998).

Staff employed in tuberculosis laboratories should be selected carefully; they should be physically and mentally capable and should accept the responsibility for practising a healthy lifestyle. Training in laboratory procedures and strict adherence to safety measures should be accompanied by a simple surveillance programme whereby the health status of laboratory staff is monitored regularly.

Disease monitoring programme for laboratory workers
Each laboratory worker should have a confidential disease monitoring file in which screening procedures for tuberculosis as well as other health-related data are recorded. The elements of a disease monitoring programme include the following:

Pre-employment profiles and baseline screening of laboratory workers
A standardised health questionnaire should be completed for each employee. This questionnaire should relate past tuberculosis infection disease, BCG vaccination status, underlying medical conditions which may compromise the susceptibility to tuberculosis and previous contact with confirmed tuberculosis cases. A model structured health questionnaire is provided in Annex 6.

A baseline chest x-ray and a Mantoux tuberculin skin test (TST) should be performed. Strongly positive reactors with skin test diameters of >15mm and symptoms suggestive of tuberculosis should be evaluated clinically and microbiologically. Two sputum specimens, collected on successive days, should be investigated for tuberculosis by microscopy and culture.

Confidential HIV testing with pre-and post-test counselling should be offered to all laboratory workers. BCG re-vaccination as a means of preventing tuberculosis in laboratory workers is not recommended.

Quarterly monitoring of health status
Laboratory workers should declare information on their health status in the form of answers to specific questions relating to the early signs and symptoms of TB. These include cough for longer than three weeks, weight loss, anorexia, night sweats and the frequent occurrence of colds or other respiratory infection episodes in recent weeks.

The laboratory worker's weight should be recorded during each monitoring exercise and an unexplained loss of more than 10% during the previous quarter should be followed up with clinical and microbiological investigations for tuberculosis.

Quarterly information on health status can be obtained by using a single structured questionnaire, as illustrated in Annex 6.

Post-exposure monitoring
Following an accident in the laboratory the laboratory workers' health monitoring file should be reviewed. S/he should be carefully monitored clinically. Eight weeks after the exposure episode a chest x-ray examination should be performed, together with a TST in cases where the baseline reaction diameter was <10mm.