HOW DIFFERENT MEASURES OF COLD WEATHER AFFECT COPD HOSPITAL ADMISSIONS IN LONDON

Laing-Morton T¹, Marno P¹, Watkin HA¹, Bryden C^{1 1}Met Office, FitzRoy Road, Exeter  EX1 3PB

Many COPD sufferers find that their symptoms become worse during colder weather, which can lead to an exacerbation resulting in hospital admission. This study investigates different measures of cold, assessing which most strongly relate to COPD admissions and whether they can be used to forecast risk of exacerbation.

COPD admissions (ICD10 J40-J44) for the 5 Strategic Health Authorities (SHAs) in London and corresponding meteorological data were extracted for October-March 1997-2003.  Correlations and regressions were used to compare the effects on admissions of:

-   daily mean, maximum and minimum temperature

-   significant drops in temperature

-   weekly average maximum temperature

-  “cumulative cold”, summing the number of degrees the daily maximum temperature was below a threshold across a week

- different windchill indices

All measures of cold showed significant negative correlations with COPD admissions.  Daily relationships were weaker than weekly ones (R=-0.19, p<0.001 for daily maximum temperature, R=-0.36, p<0.001 for weekly average maximum temperature) but are most significant with an 8 day lag.  Windchill had the strongest correlation with one week lag (R=-0.397, p<0.001) accounting for 20% of the variation in admissions.  “Cumulative cold” is also significant at p<0.001, ranging from R=0.28 for a 3°C threshold to R=0.36 for 18°C. 

Cold measures explain sufficient variation in COPD hospital admissions to be used in a forecast model of risk of exacerbation.  The Met Office uses such a model in a health forecasting and anticipatory care service in England.

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