Estimating the Induction Period of Pleural Mesothelioma From Aggregate Data on Asbestos Consumption Markku Nurminen, DPH, PhD Antti Karjalainen, MD Ken Takahashi, MD This study aimed to estimate the induction period from causal action of asbestos exposure to the manifestation of mesothelioma. We included the 9 countries for which we could find published aggregate data on the use of raw asbestos for a relevant time period. We extracted the annual numbers of cases of pleural cancer among men from the World Health Organization mortality database for those years using the International Classification of Diseases, 9th revision, classification. For the Scandi- navian countries, we used published national cancer incidence data. In autoregressive Poisson regression modeling, we invoked different time lags of the mean annual use of asbestos to specify which time span produced the best correlation between the 2 time series. The ecologic analysis suggested that the most probable estimate for the mean induction period (use versus morbidity at society level) is approximately 25 years. (J Occup Environ Med. 2003;45:1107–1115) T he future occurrence of mesotheli- oma resulting from past exposure, predominantly occupational, to as- bestos is of great interest to health authorities, workers, and society at large. Hence, estimating accurately the induction period 1 from the initi- ation of the causal action of a risk factor to the manifestation of the disease is of importance. Disease, in its initial stage, will not necessarily be apparent. The time span for which the illness remains inapparent has been termed the latent period, 1 al- though others have used this term for the time delay between exposure to a disease-causing agent and the ap- pearance of manifestations of the disease. 2 In practice, the period be- tween etiologic action and illness detection can rarely be separated em- pirically into induction and latent periods. It is also difficult to exactly assess the onset of exposure and the onset of disease on an individual level. Thus, Rothman 1 has referred to their sum, that is, the time between causal action and illness detection, as the empiric (or apparent) induction period. This is the epidemiologic concept that we are, at an ecologic level, concerned with in this article. Data from the Australian Mesothe- lioma Register, 3 the most complete mesothelioma registry extant, sug- gests that mesothelioma incidence matches asbestos consumption with an induction period of approximately 35 years (range, 20 –50 years). 4,5 The asbestos consumption was high in many countries in the 1960s and 1970s. In Australia, for example, the From the Department of Epidemiology and Biostatistics (Dr Nurminen, Dr Karjalainen), Finnish Institute of Occupational Health, Helsinki, Finland; and the Department of Environmental Epidemi- ology (Dr Takahashi), University of Occupational and Environmental Health, Kitakyushu, Japan. Address correspondence to: Markku Nurminen, Department of Epidemiology and Biostatistics, Finnish Institute of Occupational Health, Topeliuksenkatu 41 a A, FIN-00,250 Helsinki, Finland; E-mail: Markku.Nurminen@ttl.fi. Copyright © by American College of Occupational and Environmental Medicine DOI: 10.1097/01.jom.0000091682.95314.01 JOEM • Volume 45, Number 10, October 2003 1107