Short term exposure to fine particulate matter and hospital admission risks and costs in the Medicare population: time stratified, case crossover studyBMJ 2019; 367 doi: https://doi.org/10.1136/bmj.l6258 (Published 27 November 2019) Cite this as: BMJ 2019;367:l6258
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Re: Short term exposure to fine particulate matter and hospital admission risks and costs in the Medicare population: time stratified, case crossover study
At least 10% of the 2000 - 2012 Medicare population ( 95,277,169) must have been smokers who inhale 10,000 to 40,000 microgrammes per cubic metre of PM2.5 in a few minutes per cigarette (1). Compare this to a non-smoker who breathes in 1 cubic metre of air per hour, which equates to 24 cubic metres over 24 hours. Even an extra 24 microgrammes of PM2.5 is tiny compared to PM2.5 inhaled by smokers from 1 cigarette. If short term exposure to PM2.5 is linked to deaths as claimed, shouldn't there gave been over 9.5 million deaths out of the 95 million Medicare population due to the short term inhalation of PM2.5 directly from cigarette smoke?
(1) National Research Council. Environmental tobacco smoke: measuring exposures and assessing health effects. Washington, D.C.: National Academy Press; 1986.
Competing interests: No competing interests
The surprising negative correlation between air pollution and influenza requires more explanation and/or research
The article by Wei et al on the short-term health effects of PM2.5 air pollution is a further reminder of the great harm caused by particulate air pollution at a population level.
I was intrigued however, to see what appears to be a negative correlation between increasing PM2.5 air pollution and influenza infection. This can be seen in almost every graphical representation of the research findings i.e. figures 2-8.
In almost every analysis of the effects of increasing air pollution, influenza seems to decrease, one of only two medical conditions which are negatively correlated with PM2.5 air pollution in this study.
The authors have suggested this negative correlation may be due to patients with influenza being admitted or diagnosed with other medical conditions which mask the “principal discharge diagnosis”. However, no data or any other evidence is put forward to support this hypothesis.
If this is the explanation, then it should raise doubts about all other associations, since the main measured outcome “principal discharge diagnosis” takes no account of other potentially serious diseases.
Given the health effects of air pollution on the cardio-respiratory system, it is hard to see how increased air pollution can reduce the risk and/or severity of influenza infection.
It would be helpful to know whether the diagnoses of influenza were based upon clinical diagnosis, or were they laboratory-confirmed diagnoses?
This is such a surprising negative association, it warrants more detailed explanation by the authors and/or further research on this specific finding.
Wei Y, Wang Y, Di Q et al. Short term exposure to fine particulate matter and hospital admission risks and costs in the Medicare population: time stratified, case cross-over study. BMJ 2019;367:l6258 doi: https://doi.org/10.1136/bmj.l6258 (accessed 4/12/19)
Competing interests: The views expressed are my own and not those of my employer.