Table 2.

Antibiotic use by duration of use at ages 20–39, 40–59, and 60 + in 2004 and part four years in 2008 in relation to subsequent PD risk in Nurses' Health Study.

	None	1–14 days	15 days to 2 months	More than 2 months	p trend
Antibiotic use at age 20–39 a
Number of women	7,861	29,180	10,683	4,117
PY	57,781	219,757	81,379	31,611
Cases (n = 158)	19	104	23	12
HRcrudec (95% CI)	0.68 (0.42, 1.10)	Ref	0.68 (0.43, 1.06)	1.01 (0.55, 1.83)
HRmultivd (95% CI)	0.67 (0.41, 1.09)	Ref	0.67 (0.43, 1.04)	0.98 (0.54, 1.78)	0.64
Antibiotic use at age 40–59 a
Number of women	4,218	29,742	14,316	5,443
PY	31,168	223,881	108,013	40,888
Cases (n = 168)	12	91	45	28
HRcrudec (95% CI)	1.01 (0.55, 1.84)	Ref	1.16 (0.82, 1.65)	1.45 (0.89, 2.35)
HRmultivd (95% CI)	1.00 (0.55, 1.83)	Ref	1.15 (0.81, 1.64)	1.44 (0.88, 2.33)	0.59
Antibiotic use at age 60 + a
Number of women	9,001	25,953	12,900	5,568
PY	68,235	194,559	95,888	40,103
Cases (n = 170)	19	93	40	18
HRcrudec (95% CI)	0.70 (0.43, 1.15)	Ref	0.82 (0.57, 1.18)	0.89 (0.53, 1.47)
HRmultivd (95% CI)	0.70 (0.42, 1.15)	Ref	0.81 (0.56, 1.18)	0.88 (0.53, 1.47)	0.75
Antibiotic use during the past four years (reported in 2008) b
	Never	Ever	p
Number of women	13,468	39,975
PY	49,530	146,886
Cases (n = 58)	14	44
HRcrude (95% CI)d	Ref	1.14 (0.62, 2.09)
HRmultiv (95% CI)b	Ref	1.14 (0.62, 2.10)	0.67

^aReported in 2004; follow-up: 2004–2012. ^bReported in 2008; follow-up: 2008–2012. ^cAdjusted for age as a continuous variable. ^dAdjusted for age as a continuous variable, pack-years smoking (as a continuous variable), smoking (current, past, or never), and PMH use.