Cryptosporidiosis in humans: review of recent epidemiologic studies

Since 1976, when Cryptosporidium was first recognized as a human pathogen, understanding of the epidemiology of this protozoan parasite has increased substantially. This review discusses 14 recently published studies of the occurrence of cryptosporidiosis in developed and developing countries and compares their findings with those of previous epidemiologic reports. These studies show that cryptosporidiosis is an important public health problem worldwide. Although cryptosporidiosis was first recognized as a problem in immunosuppressed patients, persons with normal immunologic function are also affected. This appears to be especially true for children in developing countries; of 1035 children with diarrhea reported in several surveys, 79 (7.6%) had Cryptosporidium. Findings from studies that included both asymptomatic as well as symptomatic persons have demonstrated that Cryptosporidium infections are rare in persons without symptoms, suggesting that Cryptosporidium should not be thought of as an opportunistic parasite. Early studies documented the potential for animal-to-human transmission of Cryptosporidium, but it is now clear that many, perhaps most, Cryptosporidium infections in humans are not acquired directly from infected animals. Although alternate modes of transmission are just beginning to be explored, evidence indicates that person-to-person spread is important.