HIV infection is a major threat to the health of most nations in the world. Prevention of the spread of HIV requires major behavioural changes and the current evidence points to rather a gloomy picture. Prevention through vaccination is a hope for the future for developed countries but this hope has to be sustained with the knowledge that for the developing countries the expected large cost of vaccination would be a very major problem. Further, the travelling patterns of people mean that people from various countries will continue to be in contact. HIV infection is thus a challenging problem and efforts of a variety of people can contribute to the control of this threat.

The control of HIV infection and the care of HIV patients have to meet the challenges of complexity, uncertainty, variability, and limited resources. The modelling approach of Operational Research has grown from dealing with these challenges. This paper is mainly concerned with operational models for the care of HIV patients. The models can also provide some information for evaluating the effects of proposed preventive measures. The models can help two groups of users: Health Planners concerned with resource allocation and budgeting can use the models to obtain information about resource usage and costs over time; Clinical Staff interested in effective patient care and in the monitoring of resources used for patient care can obtain helpful quantitative information from the models.

Starting with an infected person, the natural history of HIV infection is characterised by uncertainty and variability. Clinical staff need quite detailed information about patients.