Methods for determining disease burden and calibrating national surveillance data in the United Kingdom: the second study of infectious intestinal disease in the community (IID2 study)

Table 4 Sample size calculations for prospective cohort study estimating a single UK-wide pyramid.

	England				Wales
Organism/condition	Baseline incidence¹	Reduction to be detected	Person-years	GP practices	Person-years	GP practices
All IID	19.20%	20%	2,000	20	200	2
Severe cases*	6.00%	20%	7,000	70	400	4
Campylobacter	0.87%	20%	500,000	5,000	2,400	24
Salmonella	0.22%	20%	500,000	5,000	9,500	95
Campylobacter+Salmonella	1.10%	20%	200,000	2,000	2,000	20
Campylobacter+Salmonella+ C. perfringens	1.34%	20%	100,000	1,000	1,600	16
	Scotland		Northern Ireland		UK
Organism/condition	Person-years	GP practices	Person-years	GP practices	Person-years	GP practices
All IID	200	2	65	1	2,465	25
Severe cases*	700	7	300	3	8,400	84
Campylobacter	4,200	42	1,400	14	508,000	508
Salmonella	16,400	164	5,500	55	531,400	532
Campylobacter+Salmonella	3,400	34	1,200	12	206,600	207
Campylobacter+Salmonella+ C. perfringens	2,800	28	1,000	10	106,200	107

* Severe cases are defined as those presenting to primary care
Note: Based on ability to detect a 20% decrease in incidence with 80% power and 95% precision. Required number of person-years and GP practices (recruiting 100 patients from each practice) by country, based on the relative populations of the 4 UK countries

ISSN: 1471-2288