Risk factors for sporadic cryptosporidiosis: A systematic review and meta-analysis

Cryptosporidium spp. is an important cause of gastrointestinal disease worldwide, responsible for 69 million cases of illness in 2016. Information on the sources and transmission pathways of human cryptosporidiosis results mainly from outbreak investigations. A systematic review and a meta-analysis of case-control and cohort studies were performed to determine the main risk factors associated with sporadic cryptosporidiosis. Suitable scientific articles were identified through a systematic literature search and subjected to a methodological quality assessment. From each study, odds ratio (OR) measures were extracted or calculated, as well as study characteristics such as population type, design, type of model and risk factor hierarchy. Mixed-effects meta-analysis models were adjusted by population type to appropriate data partitions. From 1985 identified references, the quality assessment stage was passed by 57 cohort and case-control studies focusing on sporadic cryptosporidiosis. The eligible studies were conducted between 1983 and 2016 and provided 568 OR categorized for meta-analysis. This meta-analysis identified travel, immunocompromising conditions, contact with infected humans, waterborne transmission (contact with recreational waters, wastewater, and consumption of untreated drinking water), contact with animals and food consumption as the relevant risk factors for sporadic cryptosporidiosis. With regards to food exposures, consumption of meat, dairy products (raw milk) and dishes consumed outside home were found significantly associated with cryptosporidiosis. The consumption of poorly washed fruits and vegetables significantly increases ORs. This meta-analysis reveals that some potential sources of Cryptosporidium such as shellfish or vegetables are under-investigated. Future case-control studies for sporadic cryptosporidiosis should include population at risk, and investigate other potential sources in relation to the genotype and the subtype of Cryptosporidium spp.