Flow of persons and visits in the study with prevalence of malaria parasitemia. SCA indicates sickle cell anemia; AS and AA are the hemoglobin phenotypes. Clinic refers to events at outpatient clinic visits; admissions refer to events during hospitalization. Number of visits refers to all visits; n is number of persons. Malaria refers to malaria parasitemia. The number after malaria is the number of episodes of malaria parasitemia, figures in parentheses is the prevalence per visit (not per person). Note that persons without SCA (non-SCA) were not part of the prospective surveillance and were seen only once.