TB infection: an exploratory study of BCG protective properties and the possible role of environmental mycobacteria.
OBJECTIVE
To evaluate the presence of environmental mycobacterial strains and explore the implications for BCG vaccination against TB.


METHODS
Multimethod approach which included structured interviews and medical records examination. Soil and water samples were analysed using standard microbiology methods.


METHODS
Beatrice Infectious Diseases Hospital, Public Health laboratories, University of Zimbabwe Medical School and several residential areas in Harare.


METHODS
129 tuberculosis inpatients at Beatrice Infectious Diseases Hospital, 26 Public Health Laboratory technicians handling TB specimens and 51 fourth year medical students.


METHODS
Vaccination status of TB inpatients, medical students and laboratory technicians, protective efficacy of BCG in all subjects, presence of environmental mycobacterium in the environment.


RESULTS
The type of tuberculosis did not differ significantly between vaccinated and non-vaccinated TB patients x2(df = 1) = 0.171 p > 0.05. There was no apparent difference between the revaccinated and non-vaccinated laboratory technicians. One respondent out of each of the revaccinated and non-vaccinated laboratory technicians had developed pulmonary tuberculosis. Among the fourth year medical students, four had positive tuberculin test results, even though they had not been vaccinated at the University clinic. Environmental mycobacteria presumptively identified as Mycobacterium scrofulaceum and Mycobacterium intracellulare were isolated from both the water and soil samples taken from a few selected areas in Harare. Of the 129 TB in-patients, 88 (68.2%) had previously been vaccinated against TB. Similarly among the 51 medical students 44(86.3%) had been vaccinated. Laboratory technicians re-vaccinated on the job were nine out of 26.


CONCLUSIONS
The results obtained seemed to indicate that BCG protective efficacy did wane with time and revaccination appeared not to be useful. Environmental mycobacterium that could influence the BCG efficacy do exist in our environment.
Chihota
V N
VN
Department of Medical Microbiology, University of Zimbabwe Medical School, Harare, Zimbabwe.
Nyazema
N Z
NZ
Mashingaidze
S
S
Mutandiro
B
B
D001500:BCG Vaccine / Q000276:immunology*; D004784:Environmental Monitoring; D006801:Humans; D015269:Mycobacterium avium Complex / Q000302:isolation & purification*; D015359:Mycobacterium scrofulaceum / Q000302:isolation & purification*; D012189:Retrospective Studies; D012988:Soil Microbiology; D011795:Surveys and Questionnaires; D013997:Time Factors; D014376:Tuberculosis / Q000382:microbiology* / Q000517:prevention & control*; D014504:Urban Health; D014871:Water Microbiology; D015030:Zimbabwe
D001500:BCG Vaccine