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Epidemiology is the study of the relationships of the various factors determining the frequency and distribution of disease. Given the prominence of socio-economic factors in the study of tuberculosis infection it is helpful to present the backdrop of general health statistics in South Africa before the specific disease figures. The sources of information are publications from the Department of National Health and Population Development up to 1993 (the main period of this research) together with the chapter written by Strebel and Seager in A Century of Tuberculosis - South African Perspectives (Coovadia and Benatar 1991). The official statistics provide a general overview but are limited by the information systems available. The health service is fragmented by the many independent health authorities and the significant contribution of the private sector. Nevertheless the efforts of the Department are laudable and provide a starting point for discussion.

General Health Trends

The two major contributing factors to the health status o f a population are the general developmental stage of the community and their general affluence. In 1988 South Africa ranked 28th in the world league table of total gross national product (GNP) and 52nd for GNP per capita (Chief Directorate 1990). South Africa is classified by the World Bank Atlas as a middle income developing country. Despite a steady growth in total gross domestic product (GDP) this economic marker per capita is deteriorating due to a high population growth. Such countries find it very difficult to provide housing, employment, education and health services adequate for the population. Poor income and land distribution together with food deprivation are frequent problems. South Africa is 54% urbanised compared with the African continent (29%) and Europe (69%). Figure 4.1 shows the population trends by ethnic origin demonstrating the exponential increase in the black inhabitants.

Figure 4.1 Population trends by South African ethnie group 30000 25000 20000 o o 15000 10000 5000 1920 1960 Year 1980 1940 2000

Black White Coloured Asian

Source ( t h i e f Directorate 1990)

The age structure o f the population has an important relation to health risks and socio­ economic factors, ifom schools for children to support systems for the elderly. In the region o f Africa the ratio o f total population to the 15-64 year age-group increased from 1.86 in 1960 to 1.94 in 1980, The estimate for the year 2000 is 1.92. This means that if the entire population is to enjoy the same share o f national production, every citizen o f working age must produce 1.93 times that share. This is the cost to be borne by populations with too many young or old persons. South Africa has similar statistics. This type o f situation naturally results in and maintains a vicious circle o f poverty, disease and ignorance.

The measure o f infant mortality rate (IMR) is the number o f infants under one year who die in a given year per 1000 live births in the same period. The trends in IMR for South Africa by ethnic group over the last 50 years show convergence at or below the WHO target o f 50/1000 by the year 2000 but there has been a worrying reversal o f the trend during the

1980's, particularly amongst the coloureds. Comparative IM R’s are 10/1000 for Europe, 55/1000 for Latin America, 78/1000 for Asia and 113/1000 for Africa.

Female life expectancy at birth is 77 years for Whites, 71 years for Asians, 65 years for C oloureds and 64 years for Blacks. In industrial market economies the female life

expectancy is on average six years longer than for men. This is four years in middle-income countries and one or two years in low-income countries. South African differences are five years for Blacks, seven years for Asians and Whites, and eight years for Coloureds.

The World Health Organisation’s Expanded Programme on Immunisation resolves to make immunisation against the six main vaccine-preventable diseases available to every child in the world by the year 2000; these six diseases are measles, tetanus, pertussis, diphtheria, poliomyelitis and tuberculosis. Table 4.1 shows the estimated average coverage of these immunisations by South Africa in 1988 compared with other areas.

Table 4.1 Percentage coverage of WHO-EPI programme (Chief Directorate 1990)

World Developed Countries

Developing Countries

Africa South Africa

DPT 3 55 63 55 36 67

Measles 58 71 56 36 69

Polio 3 50 79 46 40 63

BCG 59 59 60 55 85

The rising cost of health is a world-wide concern. In South Africa 11.7% o f total state expenditure was allocated to health in 1989 though this figure is not stratified by ethnic group. The private sector accounts for 45% of total health expenditure. 20% of the population are registered with a medical aid scheme. A further substantial number from the lower socio-economic strata use a private medical practitioner as the first contact point with the health service, although they are then referred to the public health system for secondary or tertiary care.

Tuberculosis

It was estimated in 1990 that six to ten million inhabitants of the country were infected with M. tuberculosis, with 65 000 notified cases and 6000 registered deaths each year (IBID). Epidemiologically it is helpful to consider asymptomatic infection, active disease, and outcomes (cure, death, disability, chronic disease).

Infection

There are marked differences in prevalence of infection between ethnic groups and geographical areas which are the result of large numbers of active cases of TB among adults in the black and coloured communities living in overcrowded conditions with subsequent transmission to children. Fourie has shown that the highest risk populations in South Africa are blacks living in coastal areas followed by coloureds, then blacks in inland areas (Fourie 1983a; Fourie 1983b). The Cape Coloured population experiences significant drug resistance and MDR-TB as well as increasing numbers of infections (Fourie and Knoetze 1986). Studies have shown household contacts, particularly those sharing the same sleeping area, have the highest risk of becoming infected whereas immediate neighbours of source cases have a risk which is only slightly higher than that of the general population (Nair, Ramnathrao et al. 1971; Kumar, Saran et al. 1984).

The annual risk of infection (ARI) is the probability of an individual becoming infected during a year. Styblo’s model has been used extensively to estimate this risk and trends in risk (Bleiker and Styblo 1978). The first tuberculosis prevalence survey of KwaZulu in 1974 estimated the ARI to be 1.4% (Arabin, Gartag et al. 1979). Fourie’s data estimated the range of ARI in 1982 to be 0.057% to 2.15% according to ethnic group and geographical location.

There seems to be little gender difference for risk of infection up to the age o f 10, but between 12.5 and 18.5 years 9% more males than females are infected (Packard in (Coovadia and Benatar 1991)).

hi Disease

With regard to active tuberculous disease this can be measured by prevalence (old and new cases, indicating the total disease burden at a point in time) and incidence (new cases over time, usually one year, giving the risk of becoming diseased).

Styblo suggests it is best to use population-based surveys, using culture and direct-smear microscopy of sputum as the basis for determining a case in order to estimate the prevalence of tuberculosis (Styblo 1976). Surveys to determine the prevalence o f active disease in the rural black population of South Africa were conducted by the Tuberculosis Research Institute

(TBRI) between 1974 and 1984. During this period 18 000 adults were examined and comparing the two periods the prevalence declined by 10% per year. Prevalence of tuberculosis was associated with a history of previous treatment (four to six times higher suggesting high relapse rates), age (consistent with age-specific notification rates), gender, and geographical area (between 1.8 and 3.7 times higher in coastal areas). The disadvantages of population-based surveys are that they require a large sample size, are costly and need to be repeated to obtain a guide to change in prevalence. The results are shown in Table 4.2.

Table 4.2 Bacteriological prevalence of tuberculous disease in the South African

rural black population, 1974-84

BACTERIOLOGICAL PREVALENCE (%)