If the individuals at risk for poor adherence could be identified early in their management, health care providers should, in theory, be able to intervene by tailoring the provision of treatment to enable such patients to continue their therapy. Unfortunately, the available evidence indicates that health care providers are unable to predict accurately which patients are likely to be nonadherent (21 - 23).

The literature describes over 200 variables associated with patients who default on treatment. Many of the cited determinants of adherence are unalterable, and the demonstration of a consistent association between characteristics such as gender, age group or literacy and adherence does not lead to a logical approaching to remedy the situation. Furthermore, demographic, social and other patient characteristics often relate poorly to the patient's intention or motivation and do not explain why some TB patients adhere to treatment despite having several unfavourable characteristics. Patients with TB apparently fluctuate in the intensity of their motivation to complete their treatment and admit to considering defaulting many times during their long course of therapy (24).

Many epidemiological studies have explored correlates of adherence, often examining the issue from a biomedical perspective. Within this framework the TB patient has sometimes been seen as a recipient of a treatment regimen, who should obey the instructions of the health care worker. Nonadherent patients who do not conform to these expectations have sometimes been regarded as "deviant". This approach ignores the fact that treatment behaviour is complex and is influenced by a host of factors including the patients' sociocultural setting, health beliefs and subjective experience of the illness.

Numerous psychosocial constructs have been proposed that have attempted to provide a conceptual model for thinking about health behaviour (24 - 28). The information - motivation - behavioural (IMB) skills model (29) which integrates information, motivation and behavioural skills in explaining behaviour has, however, attracted some attention as a potentially useful guide to developing interventions for enhancing adherence to TB treatment. The IMB model demonstrates that information is a prerequisite for good adherence, but is not sufficient in itself to change behaviour. Motivation and the development of behavioural skills are also critical determinants of behavioural change.