Many factors have been associated with adherence to TB treatment including patient characteristics, the relationship between health care provider and patient, the treatment regimen and the health care setting (10). One author has defined nonadherence as "an unavoidable by-product of collisions between the clinical world and the other competing worlds of work, play, friendships and family life" (11). Factors that are barriers to adherence to TB drugs can be classified as shown below.

A. Economic and structural factors

TB usually affects people who are hard to reach such as the homeless, the unemployed and the poor. Lack of effective social support networks and unstable living circumstances are additional factors that create an unfavourable environment for ensuring adherence to treatment (12).

B. Patient-related factors

Ethnicity, gender and age have been linked to adherence in various settings (13 - 15). Knowledge about TB and a belief in the efficacy of the medication will influence whether or not a patient chooses to complete the treatment (16). In addition, cultural belief systems may support the use of traditional healers in conflict with allopathic medicine (10,17). In some TB patients, altered mental states caused by substance abuse, depression and psychological stress may also play a role in their adherence behaviour.

C. Regimen complexity

The number of tablets that need to be taken, as well as their toxicity and other side-effects associated with their use may act as a deterrent to continuing treatment (18). The standard WHO regimen for the treatment of TB involves using four drugs for an initial "intensive phase" (2 - 3 months), and two or three drugs for a further "continuation" phase (6 - 8 months). Drugs may be taken daily or "intermittently" three times a week.

D. Supportive relationships between the health provider and the patient

Patient satisfaction with the "significant" provider of health care is considered to be an important determinant of adherence (19), but empathic relationships are difficult to forge in situations where health providers are untrained, overworked, inadequately supervised or unsupported in their tasks, as commonly occurs in countries with a high TB burden (20).

E. Pattern of health care delivery

The organization of clinical services, including availability of expertise, links with patient support systems and flexibility in the hours of operation, also affects adherence to treatment. Many of the ambulatory health care settings responsible for the control of TB are organized to provide care for patients with acute illnesses, and staff may therefore lack the skills required to develop long-term management plans with patients. Consequently, the patient's role in self-management is not facilitated and follow-up is sporadic.