Table 3.

Multivariate relationships between food vehicles and outcomes of attack rate and genogroup for published norovirus outbreaks

Variable†	Attack rate (n = 91)‡			Genogroup (n = 120)‡§
				GI		GI and GII
	β	s.e.	P value	OR	95% CI	OR	95% CI
Food vehicles
Produce	Reference			Reference		Reference
Shellfish	16·10	9·41	0·09	0·14*	0·02–0·96	15·14*	1·64–139·86
Ready to eat	−6·69	8·25	0·42	0·50	0·12–2·15	0·14¶	0·01–3·86
Season
Winter	Reference			Reference||		Reference||
Spring	−0·60	5·61	0·92
Summer	3·96	8·43	0·64	1·46	0·39–5·44	1·28	0·47–3·51
Autumn	−6·12	9·53	0·52
Hemisphere
Northern	Reference			Reference		Reference
Southern	−39·8*	9·40	<0·01	2·30	0·13–39·33	0·16*	0·02–0·997
Setting
Food service	Reference			#	#	#	#
Leisure	−17·76	9·76	0·07	#	#	#	#
School/daycare	28·45	17·05	0·10	#	#	#	#
Healthcare	−26·67	13·73	0·06	#	#	#	#

OR, Odds ratio; CI, confidence interval.

^†Italic covariates are eliminated by backward elimination (α = 0·05) without confounding covariate estimates.

^‡Attack rate estimates adjusted for genogroup and vice versa.

^§Reference category for genogroup is GII.

^¶Estimates obtained using logistic model and Firth correction.

^||Spring, summer, and autumn are collapsed to obtain valid estimates.

^#Variables not included due to sparse data.

^*Significant β or OR estimate.