National income, self-reported wheezing and asthma diagnosis from the World Health Survey.

The aims of this study were to quantify and describe the variations in respiratory symptoms and diagnosis prevalence across regions of the world according to national income. In 2002 and 2003, the World Health Organization implemented the World Health Survey (WHS), which used a standardised survey instrument to compile comprehensive baseline information on health and healthcare expenditure. We analysed the WHS data to assess the global patterns of self-reported wheeze and doctor-diagnosed asthma, two commonly reported measures of respiratory health. In total there were 308,218 participants with complete records, from 64 countries. The weighted mean age of the survey population was 43 yrs. Global prevalence of current wheezing symptoms ranged from 2.4% in Vietnam to 24% in Brazil; the prevalence of diagnosed asthma ranged from 1.8% in Vietnam to 32.8% in Australia. Overall, the prevalence of symptoms and diagnosis showed a U-shaped pattern with the largest prevalence reported in low- and high-income countries. The smallest prevalence was consistently found in middle-income countries. These WHS analyses have provided global prevalence estimates of wheeze and doctor-diagnosed asthma using data gathered simultaneously and consistently across six continents. These findings support the need for continued global respiratory illness surveillance for disease prevention, health policy and management.

Regression models for public health surveillance data: a simulation study.

OBJECTIVES: Poisson regression is now widely used in epidemiology, but researchers do not always evaluate the potential for bias in this method when the data are overdispersed. This study used simulated data to evaluate sources of overdispersion in public health surveillance data and compare alternative statistical models for analysing such data. If count data are overdispersed, Poisson regression will not correctly estimate the variance. A model called negative binomial 2 (NB2) can correct for overdispersion, and may be preferred for analysis of count data. This paper compared the performance of Poisson and NB2 regression with simulated overdispersed injury surveillance data. METHODS: Monte Carlo simulation was used to assess the utility of the NB2 regression model as an alternative to Poisson regression for data which had several different sources of overdispersion. Simulated injury surveillance datasets were created in which an important predictor variable was omitted, as well as with an incorrect offset (denominator). The simulations evaluated the ability of Poisson regression and NB2 to correctly estimate the true determinants of injury and their confidence intervals. RESULTS: The NB2 model was effective in reducing overdispersion, but it could not reduce bias in point estimates which resulted from omitting a covariate which was a confounder, nor could it reduce bias from using an incorrect offset. One advantage of NB2 over Poisson for overdispersed data was that the confidence interval for a covariate was considerably wider with the former, providing an indication that the Poisson model did not fit well. CONCLUSION: When overdispersion is detected in a Poisson regression model, the NB2 model should be fit as an alternative. If there is no longer overdispersion, then the NB2 results may be preferred. However, it is important to remember that NB2 cannot correct for bias from omitted covariates or from using an incorrect offset.

Proliferative activity in the colon of the mouse and its modulation by dietary starch, fat, and cellulose.

The effect of dietary starch, fat, and cellulose on colonic proliferation was studied in female C57Bl/6J mice after 4 weeks of feeding with diets containing various levels of starch (3, 36, and 57-65%), various levels of fat (corn oil, 5 and 29%) and various levels of cellulose (2 and 10%). Cell proliferation was measured by colchicine arrest and [3H]thymidine incorporation. The following parameters were analyzed: mitotic index, labeling index, and position of labelled cells along the crypt. Increasing starch content from 3 to 36% decreased cell proliferation both in low (5%) and high (29%) fat diets. By estimating simultaneously the effects of starch and fat with a single multiple regression model, we observed a decrease of mitotic index from 3.04 +/- 0.34 to 2.04 +/- 0.43 (means +/- SE) (P less than 0.05) when starch was increased from 3 to 36% regardless of the level of fat. Other proliferation parameters showed a similar pattern. Changes in dietary fat alone did not affect significantly cell proliferation. We also investigated the effect of starch at high levels (57-65%) and its interactions with cellulose. High starch (57-65%) increased the labeling index from 7.70 +/- 0.58 to 9.65 +/- 0.88 (P less than 0.05), when also considering the effect of cellulose in the multiple regression model. Cellulose by itself did not change the labeling index. Varying starch from 36 to 57-65% increased the number of cells/crypt column from 22.20 +/- 0.82 to 25.87 +/- 1.21 (P less than 0.05) and varying cellulose from 2 to 10% increased the number of cells/crypt column from 22.20 +/- 0.82 to 27.25 +/- 0.97 (P less than 0.01). The results indicate that either high or low fat diets, containing 36% starch, have the minimum proliferative effects in the mouse colon. However, diets containing high levels of both starch (57%) and cellulose (10%) may induce an increase in proliferation. These data suggest a potential beneficial effect of starch on colon proliferation.

The precautionary principle in environmental science.

Environmental scientists play a key role in society's responses to environmental problems, and many of the studies they perform are intended ultimately to affect policy. The precautionary principle, proposed as a new guideline in environmental decision making, has four central components: taking preventive action in the face of uncertainty; shifting the burden of proof to the proponents of an activity; exploring a wide range of alternatives to possibly harmful actions; and increasing public participation in decision making. In this paper we examine the implications of the precautionary principle for environmental scientists, whose work often involves studying highly complex, poorly understood systems, while at the same time facing conflicting pressures from those who seek to balance economic growth and environmental protection. In this complicated and contested terrain, it is useful to examine the methodologies of science and to consider ways that, without compromising integrity and objectivity, research can be more or less helpful to those who would act with precaution. We argue that a shift to more precautionary policies creates opportunities and challenges for scientists to think differently about the ways they conduct studies and communicate results. There is a complicated feedback relation between the discoveries of science and the setting of policy. While maintaining their objectivity and focus on understanding the world, environmental scientists should be aware of the policy uses of their work and of their social responsibility to do science that protects human health and the environment. The precautionary principle highlights this tight, challenging linkage between science and policy.

A case control study of lung cancer in Florence, Italy. I. Occupational risk factors.

A case control study of lung cancer in Florence, Italy was performed to investigate occupational risk factors for both men and women. The case series (n = 376) comprised all incident, histologically confirmed cases of primary lung cancer occurring in a three year period. Controls (n = 892) were patients in the same hospital of similar age, sex, date of admission, and smoking status with discharge diagnoses other than lung cancer or suicide. A detailed occupational history was collected from each subject directly. Logistic regression models were used to calculate odds ratios for specific occupations compared to all others. Among men, the lung cancer risk for bricklayers using firebrick and other refractory materials was elevated (adjusted odds ratio 6.5, 95% limits 2.1 and 20.9). Female hat makers, probably exposed to arsenic while making felt hats, had an elevated risk of lung cancer (6 cases versus 0 controls, p = 0.01). Risks in other occupations are discussed.

A case control study of lung cancer in Florence, Italy. II. Effect of migration from the south.

Risk of lung cancer related to region of birth in Italy was investigated among migrants to Florence, in a case control study of all histologically confirmed incident cases of primary lung cancer in a three year period in that city (n = 376). Controls (n = 892) were patients in the same hospital of similar age, sex, date of admission, and smoking status with discharge diagnoses other than lung cancer or suicide. Information on place of birth and year of migration to Florence was collected directly from each subject, along with a detailed occupational history. Logistic regression models were used to calculate the odds ratio for birth in the south of Italy relative to birth elsewhere. Male migrants from the south have an odds ratio of lung cancer of 0.5 (95% limits 0.3 to 0.7) relative to those born elsewhere. This "protective effect" is not explained by smoking or by any known occupational risk. The risk is lowest among those born on the island of Sicily (odds ratio 0.2 compared to those born in the centre-north).

Assessing health impact assessment: multidisciplinary and international perspectives.

Health impact assessment (HIA) seeks to expand evaluation of policy and programmes in all sectors, both private and public, to include their impact on population health. While the idea that the public's health is affected by a broad array of social and economic policies is not new and dates back well over two centuries, what is new is the notion-increasingly adopted by major health institutions, such as the World Health Organisation (WHO) and the United Kingdom National Health Services (NHS)-that health should be an explicit consideration when evaluating all public policies. In this article, it is argued that while HIA has the potential to enhance recognition of societal determinants of health and of intersectoral responsibility for health, its pitfalls warrant critical attention. Greater clarity is required regarding criteria for initiating, conducting, and completing HIA, including rules pertaining to decision making, enforcement, compliance, plus paying for their conduct. Critical debate over the promise, process, and pitfalls of HIA needs to be informed by multiple disciplines and perspectives from diverse people and regions of the world.

Risk of upper aerodigestive tract cancers in a case-cohort study of autoworkers exposed to metalworking fluids.

AIMS: To re-examine aerodigestive cancer risk in a cohort of autoworkers exposed to metal working fluids (MWF), using improved case definition and more recently diagnosed cases. METHODS: The autoworker cohort included 31 100 hourly workers alive on 1 January 1985 who worked at three automobile plants in Michigan. A case-cohort design was carried out that included incident cases of cancers of the larynx, oesophagus, and stomach, and a 10% sample of the cohort. A Cox proportional hazards model was used to estimate MWF exposure effects. The smoothing method of penalised splines was used to explore the shape of the underlying exposure-response curves. RESULTS: The most important finding was the association between larynx cancer incidence and cumulative straight MWF exposure. The results for oesophageal cancer were less consistent. For stomach cancer there was no evidence of excess risk. CONCLUSION: This association between larynx cancer and straight MWF exposures was consistent with a previous finding in this cohort, providing further support for a causal relation.

The mutagenicity of cigarette smokers' urine.

Using the methods of Yamasaki and Ames (1977), we have studied the mutagenicity of urine samples from 29 cigarette smokers and 14 nonsmokers. Duplicate plates at each dose yield reproducible dose-response curves, evening and 24-hour samples of smokers' urine have similar levels of mutagenic activity, as do evening samples from the same smoker from different days. Smokers' daily cigarette tar intake is correlated with urinary mutagen concentration, but the correlation achieves statistical significance only in the sub-sample of smokers over 25 years old. Mutagenic activity is also detectable in some nonsmokers, but as a group, their urinary mutagenic activity is far lower than that of smokers.

Lung cancer among textile workers in the Prato area of Italy.

The association between lung cancer and occupational exposure in the textile industry was investigated in a population-based case-referent study conducted in the Prato area of the province of Florence (Italy) where there is a concentration of textile factories. A complete response to a postal questionnaire was obtained for 207 cases (85.1%) and 440 referents (76.1%). Those who had ever worked in the textile industry had an odds ratio (OR) of 1.45 [95% confidence interval (95% CI) 1.0-2.1]; when nine different textile job titles were considered, an increased OR was observed only for rag sorters (OR 2.2, 95% CI 1.3-3.8) and weavers (OR 1.7, 95% CI 1.1-2.7). Analysis by different "time windows" showed an OR of 3.0 (95% CI 1.6-5.8) for rag sorters at work in the 1950s and an OR of 2.8 (95% CI 1.5-5.0) for weavers at work in the 1970s. This result supports the suggestion of two different carcinogenic exposures in the Prato textile industry (asbestos and mineral oils).

Visceral pleural thickening in asbestos exposure: the occurrence and implications of thickened interlobar fissures.

We evaluated fissural (ie, visceral pleural) thickening on radiographs in two asbestos-exposed study populations and a control group. Asbestos workers had an incidence of fissural thickening of 54.5% compared with 16.0% in the unexposed control group, with a strong positive statistical effect due to asbestos exposure beyond that attributable to age. Fissural thickening occurred in 85% of workers with parietal plaques and in 36% without pleural plaques. Fissural thickening occurred in 45% without radiographic evidence of pulmonary fibrosis, but it was very common (85%) in those with pulmonary fibrosis. Data analysis showed that fissural thickening responds more strongly to asbestos exposure than does plaque formation, with 21 years of asbestos exposure needed for a 50% chance of developing fissural thickening, while 31 years of exposure were needed for a 50% chance of forming pleural plaques. From a second group of 57 asbestos workers evaluated clinically, 8 were diagnosed as having asbestosis with radiographically clear lungs and fissural thickening. We conclude that visceral pleural thickening is common in asbestos exposure, that it is related to the years since first asbestos exposure, and that its presence may indicate the presence of pulmonary asbestosis, even with radiographically normal lungs.

Short-term effects of formaldehyde on peak expiratory flow and irritant symptoms.

The authors studied the respiratory effects of formaldehyde exposure among students who dissected cadavers in a gross anatomy laboratory. Peak expiratory flow and respiratory symptoms were measured before and after each weekly laboratory session. Each of 38 students was exposed to formaldehyde for 2.5 hr/wk for 14 wk. Individual, daily formaldehyde measurements averaged 1.1 ppm (standard deviation = 0.56 ppm). Multivariate models demonstrated two different time scales of effect of formaldehyde on peak expiratory flow: (1) exposure during the previous 2.5 hr reduced peak expiratory flow by -1.0% per ppm, and (2) average exposure during all preceding weeks reduced peak expiratory flow by an additional -0.5% per ppm of formaldehyde. However, the short-term exposure effect was diminished during the first 4 wk, suggesting at least partial acclimatization. Symptom reporting was also associated with exposure during the previous 2.5 hr, and similar evidence of acclimatization was observed. These results suggest that there are two different time scales of response to formaldehyde, and they emphasize the need for longitudinal studies, characterized by quantitative exposure characterization, and frequent measurements of outcome.

Risk factors in male infertility: a case-control study.

A case-control study was undertaken to evaluate environmental risk factors potentially involved in male infertility. One hundred twelve azoospermic or oligospermic subjects and 127 controls were interviewed, before sperm count results were available, about coffee and alcohol consumption, smoking habits, x-ray exposure, usual sitting posture, drug consumption, other nonoccupational risk factors, socioeconomic status, education level, and occupational history. An unmatched analysis was then conducted. None of the occupational risk factors appeared to be related to azoospermia or oligospermia. A high relative risk was associated with (1) occupation in the radioelectric industry, (2) nonsedentary clerical workers, (3) clerical work in the typographic industry, and (4) occupation in the textile industry, but none of these figures were statistically significant. Because of the population from which cases and controls were drawn, certain occupational risks could not be investigated in this study, e.g., exposure of agricultural workers to chemicals.

Magnetic field exposures in an automobile transmission plant.

Inconsistent findings from recent mortality studies of workers exposed to magnetic fields have led to calls for more detailed understanding of exposure distributions and metrics in various industries. The authors undertook personal monitoring at an automobile transmission plant to (a) learn if magnetic field exposure differences were present, (b) make assignments for a brain cancer study, and (c) compare two exposure indices. A wide range of average exposures occurred (i.e., 0.016-4.6 microtesla). Within-day variability was also large, and it reached 4 orders of magnitude for some workers. Unexpectedly, demagnetizers were found among the strong sources that contributed to elevated exposures. The authors used conventional summary measures to assign job groups to exposure categories, and they used a new index of exposure irregularity to make alternative assignments. These new assignments appeared to differ from the original ones with respect to work time in each exposure group (i.e., 54% of the work time fell into different exposure categories).