Cryptosporidium parvum: an emerging occupational zoonosis in Finland.

Background: Cryptosporidiosis has increased in recent years in Finland. We aimed to identify risk factors for human cryptosporidiosis and to determine the significance of Cryptosporidium parvum as a causative agent. Based on notifications to the Finnish Infectious Disease Register (FIDR), we conducted a case-control study and genotyped Cryptosporidium species from patient samples from July to December 2019. We also retrieved the occupational cryptosporidiosis cases from 2011 to 2019 from the Finnish Register of Occupational Diseases (FROD).

Results: Of 272 patient samples analyzed, 76% were C. parvum and 3% C. hominis. In the multivariable logistic regression analysis of 82 C. parvum cases and 218 controls, cryptosporidiosis was associated with cattle contact (OR 81, 95% confidence interval (CI) 26-251), having a family member with gastroenteritis (OR 34, 95% CI 6.2-186), and spending time at one's own vacation home (OR 15, 95% CI 4.2-54). Of the cases, 65% had regular cattle contact. The most common gp60 subtypes identified were IIaA15G2R1 and IIaA13G2R1. In FROD, 68 recognized occupational cryptosporidiosis cases were registered in 2011-2019.

Conclusions: C. parvum is the most common Cryptosporidium species found in humans in Finland and poses a moderate to high risk of occupational infection for people working with cattle. The number of occupational notifications of cryptosporidiosis increased between 2011 and 2019. Cryptosporidiosis should be recognized as an important occupational disease among persons working with livestock in Finland, criteria to identify occupational cryptosporidiosis need to be created, and occupational safety in cattle-related work should be improved.