Academic journal article Environmental Health Perspectives

A Retrospective Assessment of Mortality from the London Smog Episode of 1952: The Role of Influenza and Pollution

Academic journal article Environmental Health Perspectives

A Retrospective Assessment of Mortality from the London Smog Episode of 1952: The Role of Influenza and Pollution

Article excerpt

The London smog of 1952 is one of history's most important air pollution episodes in terms of its impact on science, public perception of air pollution, and government regulation. The association between health and air pollution during the episode was evident as a strong rise in air pollution levels was immediately followed by sharp increases in mortality and morbidity. However, mortality, in the months after the smog was also elevated above normal levels. An initial government report proposed the hypothesis that influenza was responsible for high mortality during these months. Estimates of the number of influenza deaths were generated using multiple methods, indicating that only a fraction of the deaths in the months after the smog could be attributable to influenza. Sensitivity analysis reveals that only an extremely severe influenza epidemic could account for the majority of the excess deaths for this time period. Such an epidemic would be on the order of twice the case-fatality rate and quadruple the incidence observed in a general medical practice during the winter of 1953. These results underscore the need for diligence regarding extremely high air pollution that still exists in many parts of the world. Key words: air pollution, influenza, London, mortality.


In December 1952, a thick smog settled over London, resulting in unprecedented morbidity and mortality, bringing the relationship between air pollution and health to the attention of the general public, the government, the media, and the scientific community. The Big Smoke, a 50-year commemoration of the smog, took place in London in December 2002. The conference reviewed the events leading to the episode, the health impacts of the smog, and current air pollution conditions in London and elsewhere. This revisiting of the smog reminded us that much can still be learned from the event, in terms of both how air pollution affected Londoners at the time and how health can be affected by high levels of air pollution in much of the world today.

In an earlier study (Bell and Davis 2001), we analyzed the relationship between pollution and mortality and morbidity for the London smog of 1952. Several indicators of morbidity, such as hospital admissions, showed patterns similar to those of pollution levels. Daily mortality during the smog was also associated with daily air pollution levels. Results were not sensitive to the peak day of the pollution and were not confounded by temperature. The relationship between mortality and air pollution levels lot longer periods revealed a statistically significant association between weekly ambient levels and mortality. Regression analysis showed that weekly air pollution and mortality were statistically associated, even when the week of Thus, air pollution was affecting mortality in London, aside from the extreme episode.

Mortality did not return to normal levels for several months after the episode. The strong immediate health response to the episode is evident in the coinciding sharp increase in mortality; however, the elevated mortality in the months after the smog requires a more detailed analysis. An initial government report (U.K. Ministry of Health 1954) proposed the hypothesis that influenza was responsible for the elevated mortality in the months that followed the episode. The weekly number of excess deaths in Greater London (the number of deaths exceeding those during the same time period the previous year) peaked at about 4,500 for the week ending 13 December 1952. Total mortality rates were about 80% higher than the previous year for December 1952 and were 50 and 40% higher, respectively, for January and February 1953. From December 1952 through March 1953, there were over 13,500 more deaths than normal. A fraction of these likely resulted from air pollution and a fraction from influenza.

The exact numbers of influenza-related and air pollution-related deaths are unknown and continue to generate debate (Stone 2002). …

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