• all-cause morbidity such as pneumonia or malaria (presumptive and definitive diagnosis) [ Time Frame: 3 years ] [ Designated as safety issue: Yes ]
  

• sub-clinical laboratory abnormalities (such as neutropenia) and serious adverse events (such as death) [ Time Frame: 3 years ] [ Designated as safety issue: Yes ]
  

Randomized double-blind placebo controlled equivalence trial to be conducted among consenting clinically healthy patients on HAART with 2 or more CD4 counts of 200 cells/ul or more for at least 3 months. The study will enable comparison of effects of randomized cessation of cotrimoxazole prophylaxis at 2 CD4-guided thresholds (200 Vs 350 cells/ul).

Rationale for inclusion of the placebo-controlled design

• The double-blind placebo controlled approach is feasible and ethically justified in this equipoise situation to allow for concealment of allocated intervention among investigators and patients and avoids accidental unblinding of investigators to the allocated interventions by trial patients.
• Maintenance of continued cotrimoxazole prophylaxis among patients randomized to this intervention will be easier if there is no awareness that those patients randomized to cessation of prophylaxis have a relative advantage of reduced pill burden.
• It would be very difficult to maintain cessation of cotrimoxazole prophylaxis among patients randomized to do so in our setting where cotrimoxazole is readily and cheaply available in drug shops, drug stores and pharmacies.

First randomisation

Patients who have been on HAART for at least 3 months and who have a confirmed CD4 count between 200 and 349 cells/ul will be randomized to continue prophylaxis with active cotrimoxazole or to cease prophylaxis with active cotrimoxazole but continue with ingestion of the placebo cotrimoxazole daily.

Second randomization

Patients who achieve a confirmed CD4 count of 350 cells/ul or more while on HAART will be randomized to continue prophylaxis with active cotrimoxazole or to cease prophylaxis with active cotrimoxazole but continue with ingestion of placebo cotrimoxazole daily. Some patients will have participated already in 1st randomization but others will be entering the trial at this stage for the first time.

Rationale for 4 trial arms

In order to assess the separate effects of cessation of cotrimoxazole prophylaxis in trial patients at the 2 randomization stages above, those continuing with prophylaxis will be compared with those ceasing prophylaxis, necessitating 2 arms at each stage.