The epidemiology of tuberculosis in an urban community in the Western Cape Province with a high incidence of tuberculosis

Against the above background we have, for more than a decade, studied the tuberculosis situation in a small area of the Western Cape Province, i.e. the Cape Town suburbs of Ravensmead and Uitsig (Beyers et al 1996). These suburbs, 2.34 km2 in area, had a population of 34294 during the 1991 national census. The tools involved in this evaluation include:

(1) Access to routine tuberculosis notifications.

(2) A long-standing personal relationship with clinic personnel at the suburbs' two local health authority clinics.

(3) The creation of a computerized geographical information system (GIS) map showing all of the suburbs' erven.

(4) The collection of all positive cultures which are evaluated for drug sensitivity and DNA fingerprinting (IS6110).

(5) An in-depth evaluation of sociological and anthropological aspects of the community.

This area, virtually uninhabited in 1960, grew within a decade to become a densely populated residential area. This change is testimony of the pace of urbanization in South Africa and the forced movement of people from other areas of Cape Town under the infamous Group Areas Act. The combined population of these suburbs during the 1991 census was 34294, of whom 10 775 (31%) were less than age 15 years, and 14 764 (43%) less than 20 years. About 34% of the adult population have an annual income of less than R3000 ($650) and 40% have no income.

In 1985—1994 there were 4044 notified cases of tuberculosis amongst residents of Ravensmead and Uitsig. The distribution of these cases is illustrated in Fig. 2, which is based on the GIS map. Published and unpublished data indicate that approximately 80% of cases are 'sputum' smear positive, 15% are culture positive only and just over 50% of adult patients have cavitation on chest radiography (Beyers et al 1997). During the period under review, 3539 cases of tuberculosis occurred in 1575 single-dwelling units (34%), whereas 505 cases occurred in 260 out of 663 (39%) multiple-dwelling units (flats or apartments).

The 1991 national census subdivided the suburbs into 39 enumerator subdistricts each with a population of approximately 900. Although the overall tuberculosis incidence was 1505 per 100 000 in 1991 it varied from a low of 78 per 100 000 to as high as 3150 per 100 000 in different enumerator subdistricts. The

200 400 600 BOO 1000

□ Non-residential arees

FIG. 2. Distribution of notified cases of tuberculosis in the Cape Town suburbs of Ravensmead and Uitsig 1985-1994.

200 400 600 BOO 1000

□ Non-residential arees

FIG. 2. Distribution of notified cases of tuberculosis in the Cape Town suburbs of Ravensmead and Uitsig 1985-1994.

tuberculosis incidence was also evaluated with regard to various socioeconomic factors, and a significant relationship (£<0.00004) was found for mean household income, crowding and maternal education. In Fig. 3 the tuberculosis incidence is illustrated in enumerator subdistricts grouped according to income.

Despite the intensity of the tuberculosis epidemic in this community it was surprising that IS6110-based DNA fingerprinting of 334 Mycobacterium tuberculosis isolates found a low rate of clustering (30%) suggesting relatively infrequent recent transmission (Warren et al 1996). Reactivation of latent infection may play a greater role in high incidence areas than was previously suspected.

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