Second, the absolute number of blood T cells per mm3 determines the infection prophylaxis treatment in cases of HIV; for example, people with < 200 CD4+ T cells/mm3 need trimethoprim/sulfamethoxazole prophylaxis, whereas people with < 50 CD4+ T cells/mm3 require azithromycin.163 Understanding changes in absolute blood leukocyte counts, in addition to percentages, will help determine the clinical approach to any potential immunosuppressive effects of SCI. Here, CD4 is linked to infection.