Table 2. Incidence density of pyogenic liver abscess stratified by sex, age and follow-up period between splenectomy group and non-splenectomy group.

Variable	Splenectomy				Non-splenectomy				IRR (95% CI)
	n	Event	Person-years	Incidencea	n	Event	Person-years	Incidencea
All	17 779	171	79 669	2.15	70 855	262	457 798	0.57	3.75 (3.57–3.94)
Sex
Male	11 097	106	48 677	2.18	44 219	164	284 391	0.58	3.78 (3.55–4.01)
Female	6682	65	30 993	2.10	26 636	98	173 407	0.57	3.71 (3.43–4.01)
Age group, years
20–39	7512	59	43 809	1.35	29 884	69	211 477	0.33	4.13 (3.83–4.45)
40–64	4813	59	19 769	2.98	19 180	91	121 908	0.75	4.00 (3.65–4.38)
65–84	5454	53	16 092	3.29	21 791	102	124 414	0.82	4.02 (3.68–4.38)
Follow-up period
≤1 year	17 779	82	14 697	5.58	70 855	46	69 252	0.66	8.40 (7.97–8.85)
2–3 years	13 254	35	22 004	1.59	67 766	70	120 702	0.58	2.74 (2.59–2.90)
4–5 years	9217	34	27 430	1.24	53 353	86	166 703	0.52	2.40 (2.25–2.57)
>5 years	4864	20	15 538	1.29	30 696	60	101 141	0.59	2.17 (1.99–2.37)

CI, confidence interval; IRR, incidence rate ratio (splenectomy vs non-splenectomy).

^aIncidence: per 1000 person-years.