We recorded 243 malaria episodes ( 291 per person-years ) in the 45 HIV-exposed children assigned to continue co-trimoxazole until age 4 years compared with 503 episodes ( 560 per person-years ) in the 46 children assigned to stop co-trimoxazole at age 2 years ( incidence rate ratio 053 , 95 % CI 039-071 ; p < 00001 ) .