iClinic - September 26, 2000
Peter Doyle, Metropolitan

So says Peter Doyle, currently group managing director of Metropolitan. Doyle was responsible, when still involved in actuarial research, for the development of the Metropolitan Doyle model, regarded both locally and internationally as the definitive predictor of the progression of the HIV/AIDS pandemic.

"Does HIV cause AIDS? This is the question that has been asked time and again over the past few months. Getting the 'right' answer to it has become a national obsession that is, in my opinion, distracting our attention from the real problem: how should we in South Africa be fighting the pandemic?

"It is my suggestion that we go back to basics. Asking the right questions, in the right order, is to my mind the best way of clearing up the current confusion."

Firstly, what is immuno deficiency? Everyone is agreed that it is a condition(s) that results in greater susceptibility to infection, and therefore an increase in acute and/or chronic disease.

What causes immuno deficiency? Most people concur that it has many causes, amongst others stress, deficient diet, malnutrition, inadequate hygiene, poor healthcare and repeated exposure to disease-causing agents.

People living in poverty are therefore much more likely to suffer from immuno deficiency - a social problem of overwhelming magnitude, and one that should be addressed as such.

What are immuno deficiency diseases? They are diseases that directly impair components of the immune system, rendering it less effective. Most of them are regarded as genetic, and relatively few as acquired.

What is AIDS (acquired immuno deficiency syndrome)? As defined, AIDS is an acquired immuno deficiency, with the fact that it is "acquired" being the one thing that differentiates it from other diseases of this nature.

But not only is it an acquired immuno deficiency, it is also a syndrome. The word syndrome highlights the fact that it is not a single, easily diagnosable disease, but a characteristic combination of diseases.

However, the key aspect of AIDS remains the fact that it is "acquired". And it is this fact - the very essence of AIDS - that is frequently overlooked. AIDS is only one of the many causes of immuno deficiency, and only one of a number of immuno deficiency diseases, but because it is a disease that is acquired, it has a specific origin. And that origin is HIV.

What then is HIV? HIV is the human immuno deficiency virus. From the outset, the pattern followed by AIDS suggested the spread of a viral infection. Soon after the first cases were documented, the search started for the virus that was responsible. HIV is the name that was given to the particular class of retroviruses isolated and identified during this investigation.

And so the debate returns to the original question. Does HIV cause AIDS? All the existing evidence points to the fact that it does, although it is not understood exactly how this happens.

How does HIV cause AIDS? As has already been pointed out, the exact nature of the causal relationship between the two has not been established. However, as soon as the HI virus had been identified, a test showing the presence of HIV antibodies in the blood was included in the conditions that must be present before a definitive AIDS diagnosis can be obtained.

How is the HI virus spread? There is an overwhelming body of scientific and statistical evidence proving that HIV of epidemic proportions is caused primarily by sexually transmitted infection. This is not to say that HIV cannot be transmitted by other means, such as blood transfusions, but it is imperative that we recognise that an HIV epidemic undoubtedly results from sexual transmission of the disease.

Will everyone who is infected with the HI virus eventually become AIDS-sick? Although AIDS sickness is the most likely outcome of HIV infection, it has not been proved that all HIV infected people will eventually become AIDS-sick.

In short then, the HI virus is the most likely cause of the specific acquired immuno deficiency syndrome known as AIDS. But it is equally true that HIV/AIDS is only one of many possible causes of immuno deficiency, particularly in a country beset by poverty, malnutrition and other diseases.

In themselves these social problems are conducive to the spread of HIV, and they are also likely to be exacerbated by HIV. Although other diseases may result in symptoms similar to those of AIDS, if HIV is not present in the blood, these conditions cannot, by definition, be classed as AIDS.

And it is here, perhaps more than anywhere, that an impasse has been reached.

As a nation we have allowed ourselves to be distracted by semantics and definitions. The reality is that in South Africa today an epidemic of HIV infection is at hand that will ultimately result in an epidemic of AIDS sickness.

In fact, in many areas the latter is already well underway. When the government entered into the debate, they were doing much more than simply asking whether HIV causes AIDS. They were in fact posing a far broader range of questions such as the following:

1. Are expensive combination drug therapies, developed primarily in America and Europe, the only appropriate treatment for all AIDS patients in the national healthcare system of an African country?

2. Or is there a more effective way of coping with AIDS in South Africa where we are contending with a massive epidemic of HIV infection while at the same time trying desperately to contain the impact of widespread poverty?

Expensive drug therapy may not be the most effective solution to the problem in all instances, but it cannot be overlooked in the problem-solving equation.

The eradication of poverty may not be the whole solution either, but it remains central to the wider resolve. Further debate and research on issues as crucial as these is clearly required, so let's continue to debate them, and all the other equally important HIV/AIDS-related questions.

In conclusion then, yes, scientific studies do show that HIV is the likely cause of AIDS. And yes, poverty and other social ills are definitely exacerbating the problem, both compounding and being compounded by HIV.

However, in the final analysis our goal is to find the most effective ways of fighting the HIV/AIDS pandemic. To do this we obviously need to ask, and answer, the right questions - being the questions that inspire commitment . . . result in action . . . lead to solutions.

The Doyle model

The Met-Doyle model was first published in October 1990, with a view to producing reliable estimates of the progression of HIV/AIDS in South Africa.

he model and its projections have been extensively used in Southern Africa by many sectors for the past eight years, and have performed well when used in practical applications at the sub-group and general population level.

The model is continually reviewed in the light of new demographic and population statistics, as well as interventions which may influence the course of the epidemic and result in changing incidence of infection, morbidity and mortality.

The model is able to consider various interventions into the epidemic. These include behavioural changes (increased condom usage, reduced numbers of partners etc) and medical interventions (improved treatment of STDs, vaccinations, treatment/cure of HIV-positive and AIDS-sick individuals).

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