Table 3. Association between the incidence of acute respiratory failure for different levels of average frequency of hospital and clinical visits for PM/DM and estimation of the risk of respiratory failure using multivariate Cox proportional hazards regression analysis.

Average frequency of PM/DM, per year	Event	PYs	Rate	Crude HR (95% CI)	Adjusted HR (95% CI)
Non-PM/DM cohort	335	90,336	37.08	Ref	Ref
PM/DM cohort
<8	18	2,609	68.99	1.86 (1.16–2.99)	1.78 (1.10–2.90)
8–15	37	3,216	115.05	3.09 (2.20–4.34)	2.59 (1.81–3.70)
≥16	116	1,627	712.97	18.57 (15.00–22.98)	12.2 (9.58–15.50)

Model adjusted for age, sex, CCI score, asthma, hypertension, diabetes, COPD, pneumonia, cancer, CAD, heart failure, and PVD, and medicine of oral steroid. PM/DM, polymyositis/dermatomyositis; rate, per 10000 person-years; PYs, person-years; CI, confidence interval; HR, hazard ratio; CCI score, Charlson comorbidity index score; COPD, chronic obstructive pulmonary disease; CAD, coronary artery disease; PVD, pulmonary vascular disease.