Occurrence of spp. and spp. Infection in Humans in Latvia: Evidence of Underdiagnosed and Underreported Cases.

: Protozoan parasites- and -are important causes of diarrhea with an underestimated short-term burden on childhood growth and wellbeing in children under five years of age. The main transmission routes for both parasites are food and drinking water; transmission from person to person; and, due to their zoonotic nature, from domestic or wild animals to humans. The aims of the present study were to summarize the officially reported human cases of cryptosporidiosis and giardiasis in Latvia and to assess the occurrence of and in children within a prospective prevalence study. : The number of officially reported cases of cryptosporidiosis and giardiasis in the time period of 2000-2020 was collected from the Centre for Disease Prevention and Control of Latvia. Data from a clinical diagnostic laboratory were included in the study in the period from 1 January 2008 to 31 December 2018. Additionally, a prospective study was performed, and fecal samples were collected from unique 0-17-year-old patients from January to February 2021 and tested using fluorescent microscopy. : Overall, during the 20-year period, 71 cases (mean per year = 9) of cryptosporidiosis and 1020 (mean per year = 34) cases of giardiasis were officially reported in Latvia. Meanwhile, within the prospective study, we found 35 (6.0%; 95%CI 4.3-8.1) and 42 (7.2%; 95%CI 5.3-9.6) cases. : Here, we provide clear proof that both and are underdiagnosed in Latvia, which could also be true for neighboring Baltic and European countries, where a low number of cases are officially reported. Therefore, we highlight the hypothesis that the actual number of cryptosporidiosis and giardiasis human cases in the Baltic states is higher than that officially reported, including in Latvia.