A similar rate of either any parasitic infection or cryptosporidiosis in patients with a CD4 T cell count < 200 cells/μl compared to those with a CD4 count ≥ 200 cells/μl, but with some type of diarrhea highlights the importance of providing a screening service for all patients with a CD4 count < 200 cells/μl regardless of their diarrheal status. This evidence concerns the gene CD4 and parasitic infectious disease.