We conducted this study in Kisumu, Kenya where HIV prevalence is high and malaria is highly endemic. HIV infected and uninfected adults were assigned to receive daily CTX if CD4 cell count was <350, or daily multivitamin if CD4 cell count was >= 350 or if the client was HIV negative. All clients were then followed for a total of 6 months. At specified scheduled and sick visits, clients received a physical exam, blood smears, nasopharyngeal swabs and stool samples or rectal swabs. Samples collected at baseline and during follow-up were used to measure the change in CTX resistance among P. falciparum parasites, pneumococcus isolates, and commensal E. coli.