Associations between chronic comorbidity and exacerbation risk in primary care patients with COPD

Respiratory Research

Table 1 Baseline characteristics of the COPD study population grouped by low (<2/year) versus high (≥2/year) exacerbation rate

	Patients with full follow-up (study population)^a (n = 14,603)	Subgroups of study population
Patient characteristics		Patients with <2 exacerbations/year (n = 13,709)	Patients with ≥2 exacerbations/year (n = 894)^b
Sex, male, n (%)	7,749 (53 · 1)	7,322 (53 · 4)	427 (47 · 8)^‡
Age at study baseline, years; mean (SD; range)	66 · 5 (11 · 5; 40–110)^‡	66 · 5 (11 · 6; 40–110)	67 · 4 (10 · 3; 40–93)^‡
Full dataset available (censored data), n (%)
Full data available		13,709 (93 · 9)	894 (6 · 1)
Deceased	N/A	N/A	N/A
Moved	N/A	N/A	N/A
Nursing home	N/A	N/A	N/A
Unknown	N/A	N/A	N/A
Comorbidity data
Number of comorbid diseases^c, mean (SD; range)	3 · 0 (2 · 3;0–20)^‡	3 · 0 (2 · 3;0–16)	3 · 4 (2 · 5; 0–20)^‡
Number of comorbid diseases categories^c, n (%)
0	1,777 (12 · 2)	1,700 (12 · 4)	77 (8 · 6)
1 or 2	5,305 (36 · 6)	5,021 (36 · 6)	284 (31 · 8)
3 or 4	4,258 (29 · 2)	3,977 (29 · 0)	281 (31 · 4)
5 and more	3,263 (22 · 3)^‡	3,011 (22 · 0)	252 (28 · 2)^‡
Exacerbations
Number of exacerbations^d, mean (SD; range)	0 · 75 (1 · 5;0–15)^‡	0 · 44 (0 · 8;0–2)	5 · 6 (2 · 0;3–15)^‡

SD standard deviation, N/A not applicable
^* p < 0.05, ^† p < 0.01, ^‡ p < 0.001
^a p-values displayed are calculated for the difference between patients lost to follow-up versus patients with full follow-up. Chi-square tests for categorized variables and independent t-tests for continuous variables. p < 0 · 05 was considered statistically significant
^b p-values displayed are calculated for the difference between the subgroups <2 versus ≥2 exacerbations/year. Chi-square tests for categorized variables and independent t-tests for continuous variables. p < 0 · 05 was considered statistically significant
^cpresence of any type of comorbid disease was assessed at study baseline, i.e., 1 January 2012
^dMean number of exacerbations during the study period, 1 January 2012 – 31 December 2013
Baseline characteristics of the initial population of all COPD patients (n = 16,427) and those who were lost to follow-up (n = 1,824) are reported in Appendix 3

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