Policy and Environmental Change: New Directions for Public Health

Solving major, persistent public health problems requires new policies and more aggressive, sweeping interventions that affect large populations. We need well-conceived health policies and effective interventions for environmental change, but are we likely to get them? To find out, the Directors of Health Promotion and Education and the U.S. Centers for Disease Control and Prevention initiated a study of state and local public health agencies in the United States from 1996 through 1999. Data were collected by peer- and non-peer-reviewed literature searches, key informant interviews, reviews of Internet sites, and a nationwide survey. Study conclusions found confusion about the legitimacy of advocacy, lack of priority and funding for interventions that take more time versus quick fixes, variable leadership, reluctance to take risks, and a political climate that often discourages government agencies to take on these interventions. There are successes, yet more can be done.

Promising community-level indicators for evaluating cardiovascular health-promotion programs

Rigorous evaluation of community-based programs can be costly, particularly when a representative sample of all members of the community are surveyed in order to assess the impact of a program on individual health behavior. Community-level indicators (CLIs), which are based on observations of aspects of the community other than those associated with individuals, may serve to supplement individual-level measures in the evaluation of community-based programs or in some cases provide a lower-cost alternative to individual-level measures. Because they are often based on observations of the community environment, CLIs also provide a way of measuring environmental changes--often an intermediate goal of community-based programs. The Centers for Disease Control and Prevention convened a panel of experts knowledgeable about community-based program evaluation and cardiovascular disease (CVD) prevention to develop a list of CLIs, and rate their feasibility, reliability and validity. The indicators developed by the panel covered tobacco use, physical activity, diet and a fourth group that were considered 'cross-cutting' because they related to all three behaviors. The indicators were subdivided into policy and regulation, information, environmental change, and behavioral outcome. For example, policy and regulation indicators included laws and ordinances on tobacco use, policies on physical education, and guidelines for menu and food preparation. These indicators provide a good starting point for communities interested in tracking CVD-related outcomes at the community level.

Recovering true risks when multilevel exposure and covariables are both misclassified

The authors extend previous results on nondifferential exposure misclassification to the situation in which multilevel exposure and covariables are both misclassified. They show that if misclassification is nondifferential and the predictive value matrices are independent of other predictor variables it is possible to recover the true relative risks as a function of the biased estimates and the misclassification matrices alone. If the covariable is a confounder, the true relative risks may be recovered from the apparent relative risks derived from misclassified data and the misclassification matrix for the exposure variable with respect to its surrogate. If the covariable is an effect modifier, the true relative risk matrix may be recovered from the apparent relative risk matrix and misclassification matrices for both the exposure variable with respect to its surrogate and the covariable with respect to its surrogate. By varying the misclassification matrices, the sensitivity of published relative risk estimates to different patterns of misclassification can be analyzed. If it is not possible to design a study protocol that is free of misclassification, choosing surrogate variables whose predictive value is constant with respect to other predictors appears to be a desirable design objective.

Use of multiple surveys to estimate mortality among never, current, and former smokers: changes over a 20-year interval

OBJECTIVES

This study sought to demonstrate how data from publicly available large-scale cross-sectional health surveys can be combined to analyze changes in mortality risks among never, current, and former smokers.

METHODS

Data from the 1966/68 and 1986 National Mortality Followback Surveys and the 1970 and 1987 National Health Interview Surveys were used to estimate the distribution of never, current, and former smokers among the US population at risk and decedents. Standardized mortality ratios and quotients of standardized mortality ratios were used to estimate mortality risks.

RESULTS

Generally, during the period from 1966 through 1986, mortality rates in the United States for most causes of death declined among all smoking groups. However, mortality rates from respiratory diseases increased for current and former smokers.

CONCLUSIONS

The reported changes in never and current smoker mortality risks are similar in magnitude and direction to those reported in a previous study based on longitudinal data. The use of combined data from the National Mortality Followback Survey and the National Health Interview Survey offers several advantages as an epidemiological tool.

Linear extrapolation models of lung cancer risk associated with exposure to environmental tobacco smoke

This paper presents a model to estimate the number of lung cancer deaths due to ETS exposure among the 1992 U.S. never-smoking population, based on downward linear extrapolation from the estimated risks of active smokers. The model uses several recently available data sources including an extensive review of the published literature on indoor concentration of ETS constituents measured under real-world conditions and data from the National Mortality Followback Survey and the National Health Interview Survey which furnish nationally representative estimates of the distribution of the U.S. population and the persons who died from lung cancer by sex, age, and smoking status. The linear extrapolation model estimates that five male and six female excess lung cancer deaths due to ETS exposure would be expected in the 1992 U.S. population of over 52 million never smokers age 35 and over. Explanations for differences between the results of our downward extrapolation model and those of others are presented.

Identifying and defining the dimensions of community capacity to provide a basis for measurement

Although community capacity is a central concern of community development experts, the concept requires clarification. Because of the potential importance of community capacity to health promotion, the Division of Chronic Disease Control and Community Intervention, Centers for Disease Control and Prevention (CDC), convened a symposium in December 1995 with the hope that a consensus might emerge regarding the dimensions that are integral to community capacity. This article describes the dimensions that the symposium participants suggested as central to the construct, including participation and leadership, skills, resources, social and interorganizational networks, sense of community, understanding of community history, community power, community values, and critical reflection. The dimensions are not exhaustive but may serve as a point of departure to extend and refine the construct and to operationalize ways to assess capacity in communities.

An alternative explanation for the apparent elevated relative mortality and morbidity risks associated with exposure to environmental tobacco smoke

Insofar as industrial and other blue collar workers are more likely to bring home toxic materials on their person, and also are more likely to smoke than those in other occupations, members of a household are more likely to be subject to paraoccupational exposure and belong to lower socioeconomic strata if the household contains a smoker than if the household does not contain a smoker. Thus observed differences in risk of mortality or morbidity ascribed to ETS on the basis of a comparison of households with and without smokers may be partly or entirely due to differences in paraoccupational exposure and socioeconomic strata. Similarly, differences in mortality and morbidity ascribed to paraoccupational exposure may be partly or entirely due to differences in ETS exposure that are also related to social class and to types of occupation. Unfortunately, there are no data now in existence that could help determine separately the effects of these major confounded variables. There exists, then, a situation in which two explanations are advanced for respiratory diseases among members of a household, each based on similar study populations but focused on different major risk variables: ETS on the one hand, socioeconomic status and paraoccupational exposure on the other. Properly focused investigations need to be initiated.

A critical examination of OSHA's assessment of risk associated with workplace exposure to environmental tobacco smoke

In response to a request for information on indoor air quality problems, the U.S. Occupational Health and Safety Administration (OSHA) has proposed a rule addressing indoor air quality in general, and especially environmental tobacco smoke (ETS), in indoor work environments. As justification for the proposed rule, OSHA relies on a quantitative risk assessment used to provide estimates of lifetime risk of lung cancer and heart disease associated with workplace exposure to ETS. However, there are a number of concerns regarding the OSHA risk assessment. (i) The form of the underlying mathematical model used in the risk assessment is inappropriate. (ii) OSHA was highly selective in choosing what data values to use in their risk assessment. (iii) Many data values required as input to the OSHA risk assessment model are simply not known at this time. When such values are required, known, but possibly inappropriate, values were substituted. The conclusions arrived at by OSHA on the basis of this risk assessment seem unwarranted.

Correcting standardized rate ratios for imprecise classification of a polychotomous exposure variable with limited data

The analysis of exposure misclassification has received considerable attention in the epidemiologic literature, with the result that methods for correcting many summary risk estimates for such misclassification are well known. However, the application of such methods typically requires more data than are usually published (for example, the complete set of exposure- and age-specific mortality rates). The authors show, under the assumption that exposure misclassification occurs independently of disease status and confounder level, that it is possible to obtain estimates of standardized rate ratios corrected for a given pattern of misclassification from only the published standardized risk ratios and the misclassification matrix. This technique allows readers of scientific literature to perform post hoc sensitivity analysis of published risk estimates.

Mortality from respiratory cancers (including lung cancer) among workers employed in formaldehyde industries

A joint study on effects of formaldehyde exposure in industrial populations by the National Cancer Institute and the Formaldehyde Institute, Inc. (Blair et al. [1986]: J Natl Cancer Inst 76: 1071-1084; Blair and Stewart [1989]: J Occup Med 31: 881, Blair et al. [1990]: Am J Ind Med 17:683-700) reported no significant elevation in risk ratios standardized to the general population. Using the same data as Blair et al., we compared more exposed to less exposed workers to compute relative risk for respiratory and lung cancers using a multivariate, log-linear model incorporating factors for job type (hourly vs. salaried), cumulative exposure (0.1-0.5, 0.5-2, 2+ vs. < 0.1 ppm/years), length of exposure (1-5, 5-10, 10+ vs. < 1 years), and age. Models were fit for all workers, all males, all workers less than 65 years of age, and for all males less than 65 years of age. Hourly workers have a significantly elevated relative risk when compared to salaried workers. While only high levels of cumulative exposure show a significant elevation in relative lung cancer risk, trend analyses of the coefficients of a log-linear model show a significant trend of increasing risk with increasing formaldehyde exposure. The significantly elevated respiratory and lung cancer risk for workers younger than 65 may indicate a shift of respiratory cancer mortality towards younger ages among those occupationally exposed to formaldehyde.(ABSTRACT TRUNCATED AT 250 WORDS)

Comments on the Health Effects Institute-Asbestos Research (HEI-AR) report: "Asbestos in public and commercial buildings," with emphasis on risk assessment methods used

A Health Effects Institute--Asbestos Research Report calculates the risk of exposure to environmental asbestos fibers (EAF) by downward extrapolation from the mortality of workers exposed for 20 years. This extrapolation is improper because 1) relative risks of asbestos exposure very likely are not linearly progressive; 2) the composition of EAF may not be equivalent to that in mining or fabricating; 3) the same environmental asbestos concentration probably represents different exposure doses for different populations; and 4) health effects of asbestos exposure on children, seniors, patients, the institutionalized, the handicapped, and the chronically ill may not be the same as those of healthy workers. Evidence of asbestos-related disease among family members of exposed workers demonstrates that the risk observed for EAF is substantially larger than that estimated from downward extrapolation and suggests a basis for an alternative approach to estimating asbestos-related health risks. Such epidemiologic procedures are well established and ought to form the basis for detecting the health effects of EAF. It is also unclear which industry supports HEI-AR.

Risk attribution and tobacco-related deaths

The number of deaths that would not have occurred had an exposure or trait been absent is generally estimated by observing mortality rates in sample populations of exposed and nonexposed persons and applying them to the population of interest. Three methods used to estimate deaths due to tobacco use are evaluated. Each method requires estimates of certain absolute and relative risks, and the published estimates based on them assume that the absolute and relative risks observed in the two large American Cancer Society prospective studies can be applied to the US population or to populations in developed countries. Computations using large representative samples of US decedents and of the entire US population for these methods result in estimated numbers of deaths for the US population that are substantially lower than those based on Cancer Prevention Survey-I or Cancer Prevention Survey-II. Computations also showed that controlling for confounding from two smoking-related variables results in still lower estimates of the number of excess deaths. Consequently, published results that ignore confounding and are based on nonrepresentative data overstate the contribution of smoking. It is imperative that estimates of excess deaths be based on representative data and control for relevant confounders.

Computation of relative risk based on simultaneous surveys: an alternative to cohort and case-control studies

If the same information on the distribution of risk factors is available for both the general population and a subset distinguished by some disease outcome, it becomes possible to derive relative risk estimates applicable to the entire population with the assurance that the data upon which the estimates are based is representative of that population. To illustrate this approach, data from the 1986 National Mortality Follow-back Survey and the 1987 National Health Interview Survey were used to compute rate ratios for several causes of death for work in dirtyier as compared with cleaner occupations by three methods commonly employed in cohort and case-control studies: the usual standardized rate ratio, the Mantel-Haenszel estimate of the rate ratio, and a multiplicative model fit to an appropriate cross-classification. Properly placed questions in appropriate surveys might very well serve as a substitute for cohort studies and could be performed at less cost and with less overall effort, and completed in a shorter time. Moreover, this approach is less subject to problems of representativeness than cohort and case-control studies.

Analysis of the relationship between smokeless tobacco and cancer based on data from the National Mortality Followback Survey

This study investigates the potential link between the use of smokeless tobacco and oral cancer and cancer of digestive organs. The combined data of the National Mortality Followback Survey (NMFS), a probability sample of the U.S. deaths, and the coincident National Health Interview Survey (NHIS), a probability sample of the living, non-institutionalized U.S. population, are used to compute risk estimates for cancer, oral cancer, and cancer of the digestive organs associated with use of smokeless tobacco based on a cross sectional study design, simultaneously controlled for potential confounding from active smoking, alcohol consumption, and occupational exposure. Use of smokeless tobacco (either as snuff or chewing tobacco) does not increase the risk of oral cancer or cancer of the digestive organs. Alcohol emerges as a major risk factor for oral cancer with a strong dose-response relationship between the amount of drinking and risk. The same is true to a lesser extent for cancer of the digestive organs. Smoking is associated with increased risk of oral cancer but not of cancer of the digestive organs. Blue collar, technical, and service workers have significantly increased risk of cancer of the digestive organs relative to professional, managerial, and clerical workers, but not of oral cancer. Differences between findings based on the NMFS/NHIS and those obtained from other data very likely are due to inadequate control for confounding. Other reasons for differences between the NMFS/NHIS data and other studies are discussed.

Bias in the attribution of lung cancer as cause of death and its possible consequences for calculating smoking-related risks

Most published calculations of mortality risk, especially those for lung cancer associated with smoking, are based almost exclusively on the underlying cause as recorded on death certificates. Such risk calculations implicitly assume that the conditional probability of recording lung cancer as the underlying cause of death, given that it really is the underlying cause, is the same for all exposure groups. If these probabilities are not equal for all exposure groups, we call the resulting bias a cause of death attribution bias. We analyzed the 1986 National Mortality Followback Survey, a sample of 18,733 U.S. death certificates, and the 1954-1962 Dorn study, a follow-up study of approximately 250,000 holders of U.S. Veterans Life Insurance. Both data sets include information on the smoking habits of decedents and on the underlying and contributing causes of their deaths. We found that lung cancer as an underlying cause is recorded with a much smaller relative frequency if the decedent is known to be a never-smoker and with a much larger relative frequency when the decedent is known to be a smoker. On the other hand, lung cancer as a contributing cause is recorded with a much larger frequency if the decedent is known to be a never-smoker and with a much smaller frequency when the decedent is known to be a smoker. The reverse is true for cancers other than of the lung. There is no similar pattern related to smoking for other causes of death (specifically for myocardial infarction, other chronic ischemic heart disease, diabetes, or cerebrovascular disease).(ABSTRACT TRUNCATED AT 250 WORDS)

A graphical approach to the interpretation of age-period-cohort data

Two major obstacles to the routine application of age-period-cohort models are (1) the identification problem, and (2) the fact that separate interpretation of the coefficients of the model is seldom possible. We offer a practical solution to these obstacles that involves plotting the relation between the variable of interest and the age, period, and cohort variables in such a manner that nontrivial age, period, or cohort effects are readily recognized as particular types of features in the graph. These features remain recognizable in the presence of normal sampling variability. Examples are given for applying the technique to previously published mortality data.

[Epidemiology of "sick buildings"]

The indoor environment of modern buildings, especially those designed for commercial and administrative purposes, constitutes a unique ecological niche with its own biochemical environment, fauna and flora. Sophisticated construction methods and the new materials and machinery required to maintain the indoor environment of these enclosed structures produce a large number of chemical by-products and permit the growth of many different microorganisms. Because modern office buildings are sealed, the regulation of humidification and temperature of ducted air presents a dilemma, since difference species of microorganisms flourish at different combinations of humidity and temperature. If the indoor environment of modern office buildings is not properly maintained, the environment may become harmful to its occupants' health. Such buildings are classified as "Sick Buildings". A review of the epidemiology of building illness is presented. The etiology of occupant illnesses, sources of toxic substances, and possible methods of maintaining a safe indoor environment are described.

A practical approach to estimating the true effect of exposure despite imprecise exposure classification

Accurate information on actual exposure to some possibly toxic agent usually is not available in long-term occupational studies. Any strategy for assigning exposure levels or categories necessarily results in misclassification, where some individuals classified as exposed have no real exposure and some individuals classified as not exposed have some exposure to the agent. Both misclassification errors serve to reduce the estimate of risk associated with exposure. The question arises, "How much does the true risk depart from the observed estimate given an assumed level of misclassification?" This paper quantifies the effect of such misclassification on several forms of standardized risk ratios. Our results express the true risk as a function of the apparent risk based on imprecise exposure classification and parameters representing the proportion of each of the groups that are correctly classified. In any practical situation, the apparent risk can be computed based on whatever classification scheme is being used. On the other hand, the proportions of the imprecisely classified groups actually exposed cannot. However, the investigator may have information or may make assumptions for likely ranges of values for these proportions. Given the apparent risk, estimated true risks can be calculated and plotted or represented in tabular form as a function of the proportions of actual exposure. The resulting graph or table enables the investigator to read off the range of possible true risk values based on what he is prepared to believe or what other information indicates about the range of proportions of misclassified subjects. For instance, results for a typical value of apparent risk of 1.8 show that the true risk may be twice the apparent risk with only 23% misclassification in each exposure group. The value of the true risk that would be necessary to be consistent with a given apparent risk increases rapidly as the extent of misclassification increases. We also show that, if the extent of misclassification is large, the apparent relative risk is close to 1.0 regardless of the actual value of the true risk. Therefore, a small apparent risk does not necessarily indicate that there is no occupational hazard.

The sick person effect

Very often criteria by which subjects are selected for epidemiological studies are associated in some manner with their health. The Healthy Worker Effect (HWE) or Healthy Person Effect (HPE) is well known. Little has been said about the converse case in which selection is associated with decreased health status, the Sick Person Effect (SPE). The SPE may introduce a bias for some cohort, most clinical follow-up, and some case-control studies when risks are standardized against an inappropriate referent. We demonstrate the existence of the SPE in two studies. Study 1 compares the incidence of a number of different diseases among individuals who were selected as children for medical treatment with that among their siblings. Study 2 computes the Standardized Morbidity Ratios (SmRs) for various acute and chronic diseases for individuals who have reported particular chronic symptoms. The SPE is clearly apparent for all instances where the general population is taken as the referent. The HPE and SPE may present serious problems for the validity of conclusions with respect to risk levels.

Age related changes in age of starting to smoke

The Average Age of Starting to Smoke (AASS) has been reported to decline for younger birth cohorts. That apparent decline has been used to support a conclusion of an increase in smoking among younger individuals. However, in some cases the apparent decline is an artifact of the method of computation which arises when the quantity being averaged is related to a quantity used to classify subjects for comparison. In one other case, a second type of error arises because the distribution of smoking initiation with age changed in such a way that the proportion of individuals taking up smoking at older ages declined more rapidly than the proportion starting at younger ages. In fact, comparison of the 1970 National Health Interview Survey (NHIS) to the 1979/80 NHIS shows a uniform decrease in starting to smoke among teens and preteens. Examples are discussed which show that estimates of possible disease related factors actually experienced by a cohort are possible only if other suitable data are available for comparable representative sections of the population at different time periods and for different ages.

Theory (or model) of the joint influence of occupational exposure to carcinogenic dust and to cigarette smoke and occupational lung cancer

The model seeks to explain the substantial number of occupational health studies that find that the relative risk for lung cancer for exposed versus unexposed smokers is less than the relative risk for exposed versus unexposed non or never smokers.

Comparison of smoking-related risk factors among black and white males

The lung cancer risk factors of smoking prevalence, amount smoked, and age started to smoke were compared for blacks and whites, using the 1970 and 1979/80 National Health Interview Survey (NHIS) survey data. For both survey years, proportionally more blacks were never smokers and fewer were ever smokers (although more were current and fewer former smokers). The average adult black smoker smoked approximately 65% of the number of cigarettes smoked by the average white adult. Blacks started smoking later than whites for almost all occupational categories. Thus, it could be argued that whites had higher smoking-associated risk factors than did blacks. At the same time, a much greater proportion of blacks than whites were in the types of occupation where they would have been exposed to occupational hazards. The sharp rise in and the larger incidence of lung cancer among blacks compared to whites may not be due to differences in black and white smoking, but more likely are a reflection of occupational differences.

Reanalysis of lung cancer mortality in a National Cancer Institute Study on "Mortality among industrial workers exposed to formaldehyde"

The analysis of an historical cohort study of mortality among individuals occupationally exposed to formaldehyde by Blair et al. (2) in 1986 failed to allow properly for the Healthy Worker Effect and to evaluate time integrated exposure and length of exposure simultaneously. In our reanalysis of the same data we find a risk for lung cancer, increasing with increasing cumulative exposure to formaldehyde.

Reanalysis of lung cancer mortality in a National Cancer Institute study on mortality among industrial workers exposed to formaldehyde

The results of an historical cohort study of mortality among individuals occupationally exposed to formaldehyde were announced in 1986 by Blair et al (JNCI 1986; 76:1071-1084). The study was a joint undertaking of the National Cancer Institute and the Formaldehyde Institute, and concluded, ". . .this large multiplant cohort study provided little evidence to suggest that formaldehyde exposure affected the mortality experience of these industrial workers." However, there were concerns by a number of workers that the design and analysis of the study had possibly masked an existing occupational hazard. Analyzing time-integrated exposure to formaldehyde without simultaneously considering length of exposure and comparing mortality of formaldehyde workers to mortality of the general population could have masked an increase in cancer risks because of the healthy worker effect. A copy of the data of the study was obtained from the principal investigator and reanalyzed. We find a significantly increased risk for all cancers and for lung cancer as a function of cumulative exposure when workers with higher levels of exposure are compared with those with little or no exposure while simultaneously considering length of exposure. When the risk ratio (RR) for lung cancer at less than or equal to 0.1 ppm cumulative exposure (CX) is taken as 1.0, the lung cancer RR for CX of 0.1 to 0.5 ppm is 1.41 (1.20 to 1.66), the RR for CX of 0.5 to 2.0 ppm is 1.73 (1.42 to 2.11), and the RR for CX greater than or equal to 2.0 is 1.70 (1.32 to 2.18). Hourly workers have a significantly higher RR than salaried workers (RR = 1.58).(ABSTRACT TRUNCATED AT 250 WORDS)

Concentrations of nicotine, RSP, CO and CO2 in nonsmoking areas of offices ventilated by air recirculated from smoking designated areas

The exposure of nonsmokers to environmental tobacco smoke (ETS) when smoking is relegated to designated areas that are not separately ventilated is of considerable interest. Concentrations of nicotine, respirable suspended particles (RSP), carbon monoxide (CO), and carbon dioxide (CO2) were measured in offices under different conditions of smoking regulation: smoking prohibited; smoking prohibited areas receiving recirculated air from designated smoking areas; smoking and nonsmoking sections of these designated smoking areas. Nicotine was collected by pumping air for periods of 1-8 hr at 1 L/min through sampling tubes containing a styrene divinylbenzene copolymer. RSPs (5 micron cut-off) were measured using an optical side scattering instrument. CO was measured by a direct reading electrochemical analyzer and CO2 by colorimetric detector tubes. Detection of nicotine in nonsmoking office areas that received recirculated air from smoking designated areas required sampling times of 4 hr or more. Nicotine levels in such offices were approximately 1.0 micrograms/m3. RSP, CO and CO2 concentrations were approximately the same in these offices as compared to nonsmoking offices not exposed to recirculated air from smoking areas. Providing a designated but not separately ventilated smoking area appears to be effective in eliminating most components of ETS from nonsmoking office work areas.

Smoking and hospital utilization

Remaining lifetime hospital days (RLHD) are used as estimates of possible differences in medical care costs between ever smokers and never smokers. Hospital usage by age in days per person per year comes from the 1970 U.S. National Health Interview Survey (NHIS) of some 40,000 households. Life table analysis for relative longevity of ever smokers and never smokers is based on mortality ratios presented in the American Cancer Society's Million Person Study. Results are similar to those obtained by Leu and Schaub for Swiss medical costs. There is no consistent increase in RLHD for ever smokers. In fact, male ever smokers older than 44 years and female ever smokers older than 38 years can expect fewer RLHDs than never smokers.

Changes in smoking characteristics by type of employment from 1970 to 1979/80

Changes in the distribution of smoking status between and within occupations by sex, race, and age are examined for 1970 and 1979/80, 10 years that saw rapid changes in smoking prevalence. The pattern of occupation within smoking categories remains basically unchanged, and, in fact, becomes more pronounced among males. The probability of young people taking up smoking remains tied to eventual occupational choice. The decline in smoking prevalence is larger among the employed than among those who are not employed. There has been a substantial increase in refusals to answer questions about smoking.

Health effects of phenoxy herbicides. A review

A review of epidemiological studies on the health effects of exposure to phenoxy herbicides suggests that exposure may be associated with an increased incidence of cancer and unfavorable outcomes of pregnancy. Studies on cancer have found increased risks of 5.3, 6.8 and 3.96 for soft-tissue sarcoma, 7.7 and 6.0 for stomach cancer, 2.05 for lung cancer, 4.8 for lymphoma, 2.3 for all cancers combined, and 5.2 for liver cancer after exposure to 2,4,5-T or dioxin contaminants. Several studies have suggested a possible increase in birth defects after paternal exposure. An increased risk of hydatidiform mole is suggested by Vietnamese studies on the effects of maternal exposure.

Extent, persistence, and constancy of the healthy worker or healthy person effect by all and selected causes of death

Hypotheses about the extent, persistence, and constancy for different causes of the healthy worker effect are evaluated using the data of the Dorn Study of Mortality Among US Veterans. Those data were selected because persons who qualify to serve in the armed forces have health status comparable to that of persons able to seek employment. Mortality rates for 5-year age groups and standardized mortality ratios for younger, older, and all age groups were computed and compared to those of the US population for all causes, all cancers, heart disease, stroke, and selected other causes of death. A healthy worker effect of 20% to 40% reduced mortality was shown to persist over the entire age range for the various causes. The overall effect for all causes is 27%.

Review of recent Vietnamese studies on the carcinogenic and teratogenic effects of phenoxy herbicide exposure

The methodology and results of several Vietnamese studies on the possible health effects of exposure to herbicides among the Vietnamese during the Second Indochina War are reviewed. The results of the studies appear to link either paternal or maternal exposure to herbicides to unfavorable outcomes of pregnancy. There is some evidence to suggest that the injury to reproduction diminishes over time. Two studies found statistically significant odds ratios of 4.6 and 12.0 for hydatidiform moles after exposure. One case-control study found a statistically significant odds ratio of 5.2 for liver cancer. Elevated odds ratios were also found for major externally detectable birth defects. Many of the detailed findings are in agreement with the results of animal experiments. Unfortunately, the Vietnamese do not have the resources to fully examine the health effects of phenoxy herbicides. It is our hope that recognition of the importance of the Vietnamese studies will lead to further work in this area.

Indirect health effects of relative humidity in indoor environments

A review of the health effects of relative humidity in indoor environments suggests that relative humidity can affect the incidence of respiratory infections and allergies. Experimental studies on airborne-transmitted infectious bacteria and viruses have shown that the survival or infectivity of these organisms is minimized by exposure to relative humidities between 40 and 70%. Nine epidemiological studies examined the relationship between the number of respiratory infections or absenteeism and the relative humidity of the office, residence, or school. The incidence of absenteeism or respiratory infections was found to be lower among people working or living in environments with mid-range versus low or high relative humidities. The indoor size of allergenic mite and fungal populations is directly dependent upon the relative humidity. Mite populations are minimized when the relative humidity is below 50% and reach a maximum size at 80% relative humidity. Most species of fungi cannot grow unless the relative humidity exceeds 60%. Relative humidity also affects the rate of offgassing of formaldehyde from indoor building materials, the rate of formation of acids and salts from sulfur and nitrogen dioxide, and the rate of formation of ozone. The influence of relative humidity on the abundance of allergens, pathogens, and noxious chemicals suggests that indoor relative humidity levels should be considered as a factor of indoor air quality. The majority of adverse health effects caused by relative humidity would be minimized by maintaining indoor levels between 40 and 60%. This would require humidification during winter in areas with cold winter climates. Humidification should preferably use evaporative or steam humidifiers, as cool mist humidifiers can disseminate aerosols contaminated with allergens.

Indirect health effects of relative humidity in indoor environments

A review of the health effects of relative humidity in indoor environments suggests that relative humidity can affect the incidence of respiratory infections and allergies. Experimental studies on airborne-transmitted infectious bacteria and viruses have shown that the survival or infectivity of these organisms is minimized by exposure to relative humidities between 40 and 70%. Nine epidemiological studies examined the relationship between the number of respiratory infections or absenteeism and the relative humidity of the office, residence, or school. The incidence of absenteeism or respiratory infections was found to be lower among people working or living in environments with mid-range versus low or high relative humidities. The indoor size of allergenic mite and fungal populations is directly dependent upon the relative humidity. Mite populations are minimized when the relative humidity is below 50% and reach a maximum size at 80% relative humidity. Most species of fungi cannot grow unless the relative humidity exceeds 60%. Relative humidity also affects the rate of offgassing of formaldehyde from indoor building materials, the rate of formation of acids and salts from sulfur and nitrogen dioxide, and the rate of formation of ozone. The influence of relative humidity on the abundance of allergens, pathogens, and noxious chemicals suggests that indoor relative humidity levels should be considered as a factor of indoor air quality. The majority of adverse health effects caused by relative humidity would be minimized by maintaining indoor levels between 40 and 60%. This would require humidification during winter in areas with cold winter climates. Humidification should preferably use evaporative or steam humidifiers, as cool mist humidifiers can disseminate aerosols contaminated with allergens.

The 'healthy worker effect' on morbidity rates

Studies relating mortality and occupation are difficult to interpret because of the "healthy worker effect." That effect is primarily due to the fact that individuals entering the labor force are in reasonably good health. A similar phenomenon might be expected in a comparison of morbidity among members of an occupational group with that of the general population. A comparison of morbidity among different population and occupation groups is made possible through the Household Interview Survey (HIS) of the National Center for Health Statistics. Data from the HIS for the years 1969 through 1974 were combined to form a sample classified according to race, sex, age, occupation, and occurrence of various health conditions. Among subjects between 25 and 59 years of age, age-specific morbidity ratios and standardized morbidity ratios were computed for blue-collar and professional/managerial employees and for unemployed who were either seeking or not seeking employment. There appears to be a "healthy worker morbidity effect" for chronic, but not for acute, conditions just as there is for mortality. The healthy worker effect for chronic morbidity maintains itself and, in fact, appears to increase throughout the 35-year period of stable employment. The age-specific morbidity ratio may have considerable theoretical importance for evaluating the related mortality experience of employed populations.