Abstract
The bacteriological consequences of giving long-term low-dose co-trimoxazole to children to prevent reinfection of the urinary tract were studied. Only six "break-through" infections occurred during 2637 child-months of prophylaxis. The children complied well with treatment. During prophylaxis the number of rectal coliform bacilli recovered was greatly and rapidly reduced, but at least 70% of the surviving coliform organisms remained sensitive to the two components of co-trimoxazole. Changes in sensitivity pattern were evident within a month of starting treatment and the proportion of rectal organisms resistant to sulphonamide or trimethoprim did not increase with time. After stopping co-trimoxazole prophylaxis the number of rectal organisms recoverable returned rapidly to normal, as did their sensitivities to trimethoprim and sulphonamide. Further episodes of urinary tract infection developing after prophylaxis was stopped were caused by organisms sensitive to a wide range of antimicrobial agents, including trimethoprim.