Socioeconomic deprivation increases the effect of winter on admissions to hospital with COPD: retrospective analysis of 10 years of national hospitalisation data

BACKGROUND: Admission to hospital with chronic obstructive pulmonary disease (COPD) is associated with deprivation and season. However, it is not known whether deprivation and seasonality act synergistically to influence the risk of hospital admission with COPD. AIMS: To investigate whether the relationship between season/temperature and admission to hospital with COPD differs with deprivation. METHODS: All COPD admissions (ICD10 codes J40-J44 and J47) were obtained for the decade 2001–2010 for all Scottish residents by month of admission and 2009 Scottish Index of Multiple Deprivation (SIMD) quintile. Confidence intervals for rates and absolute differences in rates were calculated and the proportion of risk during winter attributable to main effects and interactions were estimated. Monthly rates of admission by average daily minimum temperatures were plotted for each quintile of SIMD. RESULTS: Absolute differences in admission rates between winter and summer increased with greater deprivation. In the most deprived quintile, in winter 19.4% (95% CI 17.3% to 21.4%) of admissions were attributable to season/deprivation interaction, 61.2% (95% CI 59.5% to 63.0%) to deprivation alone, and 5.2% (95% CI 4.3% to 6.0%) to winter alone. Lower average daily minimum temperatures over a month were associated with higher admission rates, with stronger associations evident in the more deprived quintiles. CONCLUSIONS: Winter and socioeconomic deprivation-related factors appear to act synergistically, increasing the rate of COPD admissions to hospital more among deprived people than among affluent people in winter than in the summer months. Similar associations were observed for admission rates and temperatures. Interventions effective at reducing winter admissions for COPD may have potential for greater benefit if delivered to more deprived groups.