An update on the incidence of human giardiasis in Scotland, 2011-2018

Giardia duodenalis is one of the most common parasites in the UK to cause diarrhoeal illness. Giardiasis is likely to be significantly under-reported in the UK as laboratory testing is largely based on examining stool samples from individuals with a recent travel history. This results in the majority of locally-acquired cases going undetected. To increase awareness of giardiasis, we describe data gathered from cases reported within Scotland during 2011-2018.

All of the 21 Scottish National Health Service (NHS) diagnostic microbiology laboratories performed microscopy examination to detect Giardia cysts in stools, from mostly travel-related cases. The exception was one laboratory that implemented an antigen-based enzyme immunoassay in 2015. This resulted in every submitted stool being tested for Giardia. Laboratory-confirmed cases of giardiasis were reported to Health Protection Scotland (HPS) via the Electronic Communication of Surveillance in Scotland (ECOSS) during the eight-year period. Data for calculating the incidence per 100,000 of the population were obtained from the National Records of Scotland mid-2018 population estimates in Scotland.

A total of 1631 Scottish cases were reported during 2011-2018 (8-year mean: 204; range: 166-269). National Health Service Grampian, Borders and Lothian reported the highest incidence of Giardia (9.8, 7.5 and 6.7 per 100,000, respectively), all of which were above the Scottish mean incidence (3.8 per 100,000). Following the implementation of antigen testing in NHS Grampian during 2015, reports significantly increased 3.6-fold (P = 0.005). The highest incidence of giardiasis occurred in the 20-49 years age group (mean 5.4 per 100,000). Of interest, the mean incidence of giardiasis was significantly higher in males than in females (4.8 versus 3.1 per 100,000, respectively; P < 0.0001).

This report highlights the need to capture enhanced information on every laboratory-confirmed case of giardiasis to gain a better understanding of the local sources and transmission pathways occurring in Scotland. In addition, implementing sensitive, automated technologies across UK NHS diagnostic microbiology laboratories to permit the efficient, routine testing of every submitted stool for Giardia, should be encouraged to ensure all cases are identified and treated appropriately.