Exposures associated with sporadic Cryptosporidium infection in industrialised countries: a systematic review

Transmission of Cryptosporidium can occur via contaminated food or water, contact with animals or other people. Exposures are often identified from outbreak investigations, but sources for sporadic disease and pathways to infection are still unclear. The aim of this review is to consolidate the literature to describe exposures associated with human cryptosporidiosis in industrialised countries. Methods followed the recommendations made in the Cochrane Handbook for Systematic Reviews of Interventions. Three steps were used to identify the literature including electronic database searching using PubMed, Scopus and Web Of Science; reference list trawling; and an exploration of the grey literature. Quality was assessed using the Newcastle-Ottawa Scale. Screening of results was undertaken by two reviewers and data extracted using a standardised form. A narrative summary presented. Papers were included if they reported on sporadic cases and were published between 2008 and 2018. Exposures were grouped into pathways. After full-text screening, eight articles (comprising 11 studies) were included, and seven (comprising 10 studies) were suitable for further synthesis. None of the identified grey literature was included. Four studies described case-control methods, two were case-case studies and one cross-sectional. Study year ranged from 1999 to 2017 and the studies were conducted in five, large countries in three continents: Europe (UK and the Netherlands), North America (USA, Canada), and Australia. Included papers investigated water and animal exposures most frequently. Recreational water was not a major source of sporadic illness in this review. The person-to-person pathway represented the most consistent finding, with all three studies reporting on contact with a symptomatic individual demonstrating correlations between exposure and disease. This applied particularly to the home environment, which is increasingly understood to be a significant setting for spread of Cryptosporidium infection. Further work on this would help support public health messaging on preventing spread of disease at home. Systematic review registration: PROSPERO number CRD42017056589.