Table 2.

Relative risk of breast cancer according to infectious mononucleosis (ever/never and age at onset) in NHS II, 1989–2007

	RR and (95% CI) b
IM (yes/no)
Cases/ person year	(422/281,327) / (1,927/ 1,299,971)
Age Adjusted RR†	1.03 (0.93–1.15)
Multivariable RR§	1.00 (0.90–1.11)
Age at IM	No IM	≤15	16–19	20–24	25–29	30+
Cases/ person year	1,927 / 1,299,971	69 / 63,811	186 /120,546	92/ 55,871	33/15,777	34/ 21,935
Age Adjusted RR†*	1.00	0.79(0.62–1.00)	1.06(0.91–1.24)	1.08(0.88–1.34)	1.45(1.02–2.04)	1.02(0.73–1.43)
Multivariable RR§	1.00	0.77(0.60–0.97)	1.03(0.88–1.19)	1.03(0.83–1.27)	1.45(1.02–2.04)	1.02(0.72–1.43)

^†Relative Risk and 95% confidence interval from age (5 year categories) adjusted Cox proportional hazards model.

^§Relative Risk and 95% confidence interval from model above (†) additionally controlling for variables mentioned in Table 2.

^*p for linear trend < 0.05, however, data suggest a non-linear relation and trend is driven by increased risk in 25–29 category.