Variables | Univariate analysis | Multivariable analysis | ||
---|---|---|---|---|
 | Difference in mean | p-value | Difference in mean | p-value |
Age distribution | ||||
 Adult | Reference |  |  |  |
 Children | 2.7 | 0.6 |  |  |
 Mixed ages | 1.5 | 0.6 |  |  |
Year of study | ||||
 Pre 1950 | Reference |  |  |  |
 Post 1950 | 6.8 | 0.01 | −3.9 | 0.1 |
Attack rate | −0.14 | 0.05 | −0.26 | 0.07 |
Setting | ||||
 Restaurant | Reference |  |  |  |
 Catered meal | −0.5 | 0.9 |  |  |
 Community | −8.3 | 0.1 |  |  |
 Experimental | −7.4 | 0.2 |  |  |
 Outdoor activity | 1.5 | 0.8 |  |  |
 Picnic | −6.9 | 0.2 |  |  |
Food category | ||||
 Other | Reference |  |  |  |
 Dairy | −4.3 | 0.3 |  |  |
 Non-food | 3.1 | 0.6 |  |  |
 Red meat | 0.1 | 0.9 |  |  |
 Salad & vegetable | 3.3 | 0.5 |  |  |
Vaccine history | ||||
 None | Reference |  |  |  |
 Yes | 10.3 | 0.03 | 4.2 | 0.1 |
Specific case definition | ||||
 No | Reference |  |  |  |
 Yes | −2.2 | 0.4 |  |  |