• Matthew Gittins, Roseanne McNamee, Melanie Carder, Iain Beverland, and Raymond M Agius.
• Biostatistics Group, University of Manchester, Jean McFarlane Building, Oxford Road, Manchester M13 9PL, England, UK. Matthew.Gittins@manchester.ac.uk.
• Environ Health Glob. 2013 Nov 7; 12: 97.

BackgroundShort-term associations have been demonstrated between air pollution and respiratory mortality including pneumonia. Studies typically estimate exposure based only on place of residence, yet many are in hospital prior to death. This study investigates lag length and tests the hypothesis that the effect of 'black smoke' is greater when restricted to pneumonia deaths in the community - Community Deaths from Pneumonia.MethodsA time-stratified case-crossover design using conditional logistic regression estimated the daily percentage increase in risk of pneumonia mortality in relation to 'black smoke' in the preceding 30 days. Cases were pneumonia deaths in Edinburgh 1981-1996. Multiple 'control' periods, were defined using the same weekdays for the same month as the case death. Lag structure was investigated by a stratified lag model with five 6-day periods and by distributed lag models. Hospital admissions data, defined a community death as someone who had not been in hospital in any of the 30 days before death.ResultsOf 14,346 subjects who died from pneumonia, 7,536 were community deaths. Larger estimated increases in risks were seen in the community for all lag periods. Both stratified and distributed lag methods suggested positive effect estimates for 18 days after exposure and negative thereafter; the average percent increase per day across the 18 days was 0.70% (95% C.I. 0.29-1.14) for community subjects and 0.30% (95% C.I. 0.03-0.59) for all subjects.ConclusionsStudies which fail to account for hospitalisation may underestimate exposure effects as stronger pollution effects on mortality were evident in community based subjects.

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