Spatial patterns in excess winter morbidity among the elderly in New Zealand

Abstract

It has been established in New Zealand and internationally that morbidity and mortality tends to rise during colder winter months, with a typical 10-20% excess compared to the rest of the year. This study sought to investigate the spatial, temporal, climatic and demographic patterns and interactions of excess winter morbidity (EWMb) among the elderly in New Zealand. This was achieved through analysis of acute hospital admissions in New Zealand between 1996 and 2013 for all patients over the age of 60 with an element of circulatory or respiratory disease (N=1,704,317) including a primary diagnosis of circulatory (N=166,938) or respiratory (N=62,495) disease. A quantitative approach included ordinary least squares and negative binomial regression, graphical analysis and age standardisation processes. Admission rates and durations were regressed against a set of 16 cold spell indicators at a national and regional scale, finding significant spatial variation in the magnitude of EWMb. EWMb was ubiquitous across New Zealand despite climatic variation between regions, with an average winter excess of 15%, and an excess of 51% for chronic obstructive pulmonary disease (COPD). Statistically significant relationships were found between hospital admission durations and cold spells up to 28 days prior; however the magnitude would not be expected to have a significant impact on hospital resources. Nonetheless, there is potential for preventative public health strategies to mitigate less severe morbidity associated with cold spells. Patients over the age of 80 were particularly vulnerable to EWMb; however socioeconomic deprivation and ethnicity did not affect vulnerability. Patients residing in areas of high socioeconomic deprivation or identifying with Maori or Pacific Island ethnicity experienced significantly shorter admissions than other groups, and this warrants further investigation. Further investigation into winter COPD exacerbations and non-climatic factors associated with the EWMb are recommended. A comprehensive understanding of EWMb will enable preventative measures that can improve quality of life, particularly for the elderly population.