Changing Molecular Profiles of Human Cryptosporidiosis Cases in Scotland as a Result of the Coronavirus Disease, COVID-19 Pandemic.

, the most frequently reported parasite in Scotland, causes gastrointestinal illness resulting in diarrhoea, nausea and cramps. Two species are responsible for most cases: and (). Transmission occurs faecal-orally, through ingestion of contaminated food and water, or direct contact with faeces. In 2020, the COVID-19 pandemic led to global restrictions, including national lockdowns to limit viral transmission. Such interventions led to decreased social mixing, and reduced/no local and international travel, which are factors associated with transmission of multiple communicable diseases, including cryptosporidiosis. This report assessed the impact of the pandemic on Scottish cryptosporidiosis cases, and identified changes in circulating molecular variants of species. Molecular data generated using real time PCR and GP60 nested-PCR assays on laboratory-confirmed cryptosporidiosis cases reported during 2018-22 were analysed. The Scottish Microbiology Reference Laboratories (SMiRL), Glasgow, received 774 -positive faeces during 2018-22, of which 486 samples were successfully subtyped. During this time period, ( = 155; 21%) and ( = 572; 77%) were the most commonly detected species. The total number of cases during 2020, which was greatly affected by the pandemic, was markedly lower in comparison to case numbers in the 2 years before and after 2020. The most predominant family detected prior to 2020 was the Ib family which shifted to the Ie family during 2022. The most common variant during 2018-22 was the IIa family, however a rise in the IId family was observed ( = 6 in 2018 to = 25 in 2022). The dominant subtype IbA10G2, which accounted for 71% of subtypes in 2018-19 was superseded by three rare subtypes: IeA11G3T3 ( = 15), IdA16 ( = 8) and IbA9G3 ( = 3) by 2022. Frequently reported subtypes in 2018-19 were IIaA15G2R1 and IIaA17G1R1, accounting for 59% of total subtypes. By 2022, IIaA15G2R1 remained the most common ( = 28), however three unusual subtypes in Scotland emerged: IIdA24G1 ( = 7), IIaA16G3R1 ( = 7) and IIaA15G1R2 ( = 7). Continuous monitoring of variants following the pandemic will be essential to explore further changes and emergence of strains with altered virulence.