Sporadic Cryptosporidiosis Case-Control Study with Genotyping

We report a case-control study of sporadic cryptosporidiosis with genotyping of isolates from casepatients.A postal questionnaire was completed by 427 patients and 427 controls.We obtained genotyping data on isolates from 191 patients; 115 were Cryptosporidium hominis, and 76 were C. parvum.When all cryptosporidiosis cases were analyzed, three variables were strongly associated with illness: travel outside the United Kingdom, contact with another person with diarrhea, and touching cattle.Eating ice cream and eating raw vegetables were both strongly negatively associated with illness.Helping a child <5 years of age to use the toilet and the number of glasses of tap water drunk at home each day were also independently positively associated with risk.Eating tomatoes was negatively associated.For C. hominis infections, the strongly significant risk factors were travel abroad and changing diapers of children <5 years of age.For C. parvum, eating raw vegetables and eating tomatoes were strongly negatively associated with illness; touching farm animals was associated with illness. C ryptosporidiosis is due to infection by one or morespecies of the genus Cryptosporidium.Approximately 12 species are now recognized; two, C. hominis (previously known as C. parvum, genotype 1) and C. parvum (previously known as C. parvum, genotype 2), are the most important pathogens for humans (1).C. hominis is reported as being largely restricted to humans, and C. parvum is found in a wide range of animals (particularly cattle and sheep) as well as humans.Most of what we know about the risk factors for Cryptosporidium infection was learned from outbreak investigations.Outbreaks have been associated with drinking water from public and private supplies, swimming in swimming pools, consumption of unpasteurized milk, and contact with farm animals, especially during farm visits.However, most cases of cryptosporidiosis are due to sporadic rather than outbreak-associated infections.Outbreaks represent <10% of all cases of Cryptosporidium infection (2,3), although a further proportion of cases will likely be associated with undetected outbreaks (4).Truly sporadic disease may not necessarily be due to the same causes (5).Only one substantive case-control study of sporadic cryptosporidiosis in the immune-competent population has been conducted in an industrialized nation (6).We are aware of only two other case-control studies of cryptosporidiosis in non-immune-compromised persons conducted in an industrialized nation (7,8); both studies were relatively small.One, from New Mexico, found an association with drinking water, although cases may possibly have represented an undetected outbreak (7).The other study, from Australia, found a borderline association with drinking bottled water.Concerns about the safety of the spring water on sale suggested that cases in this study may also have been part of an outbreak (8).We report a large case-control study conducted in the North West Region of England and in Wales.The study was designed to investigate the etiology and epidemiology of sporadic cryptosporidiosis.The North West region has a history of a several large waterborne outbreaks of cryptosporidiosis over the past decade; Wales has not had any reported waterborne outbreaks. MethodsA case-control study was conducted in the North West of England and Wales from February 2001 to May 2002.