Impact of the COVID-19 restrictions on the epidemiology of Cryptosporidium spp. in England and Wales, 2015-2021: a time series analysis

Introduction. In England and Wales, cryptosporidiosis cases peak in spring and autumn, associated with zoonotic/environmen-tal exposures symbolscript symbolscript spring/autumn) and overseas travel/water- based activities symbolscript symbolscript autumn). Coronavirus disease 2019 (COVID- 19) restrictions prevented social mixing, overseas travel and access to venues (swimming pools/restaurants) for many months, potentially increasing environmental exposures as people sought alternative countryside activities. Hypothesis. COVID- 19 restrictions reduced incidence of symbolscript symbolscript cases and potentially increased incidence of symbolscript symbolscript cases. Aim. To inform/strengthen surveillance programmes, we investigated the impact of COVID- 19 restrictions on the epidemiology symbolscript C. hominis symbolscript C. parvum symbolscript Methodology. Cases were extracted from the Cryptosporidium Reference Unit (CRU) database (1 January 2015 to 31 December 2021). We defined two periods for pre-and post-COVID- 19 restrictions implementation, corresponding to before and after the first UK -wide lockdown on 23 March 2020. We conducted a time series analysis, assessing differences in symbolscript symbolscript and symbolscript symbolscript incidence, trends and periodicity between these periods. Results. There were 21 304 cases symbolscript symbolscript 246; symbolscript hominis=9058). Post-restrictions implementation incidence of symbolscript symbolscript dropped by 97.5 % (95 % CI: 95.4-98.6 %; P<0.001). The decreasing incidence trend pre-restrictions was not observed post-restrictions implementation due to lack of cases. No periodicity change was observed post-restrictions implementation. There was a strong social gradient; there was a higher proportion of cases in deprived areas. For symbolscript symbolscript post-restrictions implementation incidence fell by 49.0 % (95 % CI: 38.4-58.3 %; P<0.001). There was no pre-restrictions incidence trend but an increasing incidence trend post-restrictions implementation. A periodicity change was observed post-restriction implementa-tion, peaking 1 week earlier in spring and 2 weeks later in autumn. The social gradient was the inverse of that for symbolscript symbolscript Where recorded, 22 % of symbolscript symbolscript and 8 % of symbolscript symbolscript cases had travelled abroad. Conclusion. symbolscript symbolscript cases almost entirely ceased post-restrictions implementation, reinforcing that foreign travel seeds infections. symbolscript symbolscript incidence fell sharply but recovered post-restrictions implementation, consistent with relaxation of restrictions. Future exceedance reporting for symbolscript symbolscript should exclude the post-restriction implementation period but retain it for symbolscript symbolscript (except the first 6 weeks post-restrictions implementation). Infection prevention and control advice should be improved for people with gastrointestinal illness (GI) symptoms to ensure hand hygiene and swimming pool avoidance.