Table 2.

Univariate analyses for biological factors. Values are numbers (percentages) unless otherwise indicated

Variable	Cases	Controls (n=144)	Matched odds ratio (95% CI)	P value
Preceding illness*	76/144 (53)	45/144 (31)	2.3 (1.4 to 3.7)	0.001
Preceding illness (controlled for “high” season of meningococcal disease)	—	—	2.0 (1.2 to 3.3)	0.006
Epstein-Barr virus (positive for viral capsid antibody IgG)	105/129 (81)	89/116 (77)	1.8 (0.9 to 3.6)	0.12
Mannose-binding lectin (very low producers)	20/112 (18)	13/111 (12)	1.3 (0.6 to 3.0)	0.53
Influenza H3N2 convalescent titre >320	48/116 (41)	45/120 (38)	1.2 (0.6 to 2.2)	0.63
Influenza H1N1 convalescent titre >320	16/116 (14)	16/120 (13)	0.8 (0.3 to 2.1)	0.62
Influenza B convalescent titre >80	10/116 (9)	8/120 (7)	1.2 (0.4 to 3.5)	0.78
Received meningococcal vaccination (polysaccharide or conjugate)	37/144 (26)	54/143 (38)	0.4 (0.2 to 0.8)	0.01
Born at less than 37 completed weeks of pregnancy	14/142 (10)	7/140 (5)	2.2 (0.8 to 5.7)	0.12

^*In the fortnight period before illness (cases) or interview (controls).