Do patients with recurrent episodes of campylobacteriosis differ from those with a single disease event?

BMC Public Health

Table 1 Incidence rates according to patient characteristics

	First episode (11 years of follow-up)			Second episode (5 years of follow-up)			Ratio in rates^c
Charac-teristics	Average population at risk per year	Cases^a	Episode per year per 100,000 (95% C.L)	Effective population at risk^b	Cases^a	Episode per year per 100,000 (95% C.L)
Gender
Male	3,519,216	15,742	40.7 (40.0, 41.3)	12,485	163	262.8 (222.5, 303.2)	6.5
Female	3,687,208	13,142	32.4 (31.9, 33.0)	10,540	121	230.9 (189.8, 272.1)	7.1
Age category (yrs) ^d
≤4	389,854	2,406	56.1 (53.9, 58.4)	1,272	16	252.9 (129.0, 376.8)	4.5
5-14	890,700	2,774	28.3 (27.3, 29.4)	2,406	22	183.6 (106.9, 260.3)	6.5
15-44	3,097,425	15,351	45.1 (44.3, 45.8)	8,252	176	430.7 (367.1, 494.3)	9.5
45-64	1,872,161	5,262	25.6 (24.9, 26.3)	3,244	40	247.8 (171.0, 324.6)	9.7
≥65	955,915	3,032	28.8 (27.8, 29.9)	1,944	26	269.0 (165.6, 372.4)	9.3
Urbanicity ^e
Rural	893,415	4,209	42.8 (41.5, 44.1)	3,247	62	385.6 (289.6, 481.6)	9.0
Semi-urban	3,438,014	15,876	42.0 (41.3, 42.6)	12,780	170	267.8 (227.6, 308.1)	6.4
Urban	2,875,304	8,632	27.3 (26.7, 27.9)	6,889	51	148.6 (107.8, 189.4)	5.4
Total	7,206,733	28,905	36.5 (36.0, 36.9)	23,041	284	248.0 (219.2, 276.9)	6.8

Incidence rate of reported cases of campylobacteriosis with 95% confidence limits for first and consecutive episodes according to patient characteristics, Quebec, 1996-2006
^a Total number of cases observed during the follow-up period.
^b The effective population at risk (n_i') is the total number of individuals followed in the 5-year period (n_i) minus half the number of individuals censored (w_i) (n_i' = n_i-w_i/2).
^c Estimated incidence rate for second episode vs. first episode.
^d For the first episode, the age category is the age at the time of the episode (case) and census data for the age group (population). For the second episode, patients were included in the analysis only for the period during which they were in the age category and if they had had an episode in the previous 5 years.
^e Region of residence at time of first episode.

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