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How Much Smoke Do We Need in Order to Assume That There Is a Fire?

The recent article by Nino Künzli and colleagues (1), investigating the health effects of the 2003 Southern California wildfires in a group of children, found an association between the environmental levels of particulate matter (PM₁₀) and clinical outcomes, including cough, asthma symptoms, physician visits, and missing school. Surprisingly, there was a stronger association with the duration of the smell of fire.

This finding raises a number of concerns. Are the authors implying that future studies should rely on the subjective assessment of the duration of the smell of fire rather than the objective measurement of PM? Furthermore, as the study found that the smell of fire smoke and the level of PM₁₀ were highly correlated, this raises the point of the usefulness of the measurement of PM when simpler and cheaper questionnaires investigating the duration of the smell of smoke are a better predictor of clinical outcomes. The authors acknowledge that the use of questionnaires may be biased in this scenario—could this be the best explanation for the discrepancies above? Even though some of the authors of the current article have previously proved the validity of annoyance scores to assess pollution exposure (2), crucially, this has never been proved for wildfire smoke, which not only is by definition different in its composition from traffic pollution but also occurs acutely and in unusual circumstances.

Künzli and colleagues and the accompanying editorial (3) rightly point out that there may have been a significant spatial variation in smoke concentrations within each community, justifying the fact that the different exposure measures did not coincide. However, I do not see this statement as a confirmation of the validity of the study. On the contrary, this may indicate that neither the measure of smell duration nor PM levels reflected the true exposure to wildfire in this specific study.

The fact that this study proves what was expected seems to have been used in the editorial to prove the validity of the conclusions. This is of concern, since a study should be designed to prove or disprove an hypothesis and not the other way around.

Paolo Paredi

National Heart & Lung Institute, Imperial College, London, United Kingdom

FOOTNOTES

Conflict of Interest Statement: P.P. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

REFERENCES

1. Künzli N, Avol E, Wu J, Gauderman WJ, Rappaport E, Millstein J, Bennion J, McConnell R, Gilliland F, Berhane K, et al. Health effects of the 2003 Southern California wildfires on children. Am J Respir Crit Care Med 2006;174:1221–1228.[Abstract/Free Full Text]
2. Oglesby L, Künzli N, Monn C, Schindler C, Ackermann-Liebrich U, Leuenberger P. Validity of annoyance scores for estimation of long term air pollution exposure in epidemiologic studies: the Swiss Study on Air Pollution and Lung Diseases in Adults (SAPALDIA). Am J Epidemiol 2000;152:75–83.[Abstract/Free Full Text]
3. Vedal S. Where there's fire, there's smoke. Am J Respir Crit Care Med 2006;174:1168–1169.[Free Full Text]

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