Estimation of Exposure to Agent Orange and Other Defoliants among American Troops in Vietnam: a Methodological Approach

Two pivotal problems in determining whether exposure to herbicides has caused disease in Vietnam veterans or their offspring are definition of which troops were exposed and extent of exposure. The DoD HERBS tape is the most complete publicly available record of herbicide spraying in Vietnam. It contains about 17,000 records consisting of coordinates of spray missions, dates, chemical agent, quantity and area sprayed, and mission purpose. We have developed a set of discrete and continuous indexes of probability of exposure to herbicides for individual veterans. These probability indexes are based on HERBS tape spray data and on locations and dates of service derived from a place-and-date matrix completed by the veteran. They can take into account a conservative estimate of environmental persistence of herbicide by using first-order exponential decay kinetics with an estimated half-life of dioxin. Mean values for the continuous exposure probability indexes were significantly greater among veterans judged to be exposed according to self-reported job titles and specific military experiences than among men judged unlikely to have been exposed. Probabilistic exposure indexes based on HERBS tape for classification of likely exposure to herbicides in South Vietnam during 1965-1971 appear to be well suited for comparative classification of veterans and hence for use in epidemiologic studies

Wynder, Ernst

This short biographical entry outlines the career of cancer research and epidemiology pioneer Ernst L. Wynder (1922-1999)

Application of three-dimensional interactive graphics in X-ray crystallographic analysis

A program called XpY was written for the PDP-10/LDS-1 at the Princeton University Computer Graphics Laboratory, for generating and displaying models of dinucleoside phosphates. The molecule GpC, a member of this class and a fragment of the nucleic acid RNA, was subjected to X-ray diffraction analysis. The paper describes the importance of model building in X-ray analysis, and shows step by step how XpY was used to deduce the atomic coordinates of GpC from the experimental data. The program documentation is also included as an Appendix. A subjective critique of graphics is made in the Conclusions section

Remembering Ernst Wynder

In this letter to the American Journal of Public Health I add some personal observations to Sir Richard Doll’s memorial tribute to cancer epidemiology pioneer Ernst Wynder that was published earlier in AJPH

Commentary on Liu et al, ‘Prevalence and patterns of tobacco smoking among Chinese adult men and women: findings of 2010 national smoking survey’

Loomings I first became cognizant of the massive public health problem of tobacco use in China at a 1985 IARC conference in Moscow organised by David Zaridze and Richard Peto (later Sir Richard), where Yu-Tang Gao of the Shanghai Cancer Institute reported that “about half of the male adults in Shanghai are smokers.”1 Smoking prevalence in the USA had not been that high since the early 1970s; by 1985 it was 36.8% in US white males2 and only 23.6% in more than half a million male participants in Cancer Prevention Study 2.

Are Babies Normal

Clemons and Pagano suggested that certain anomalies in the distribution of birth weights are an artifact of digit bias arising when some hospitals report weight in grams and others in pounds and ounces. In this letter I report yet another administrative source of bias in New York City reports of low birthweight, namely, under-reporting of short-lived infants by hospital staff with incomplete knowledge of Health Code requirements. These infant deaths are often identified by NYC Department of Health inspection of medical records in selected hospitals known to have many high-risk births

Computer Graphics in the Solution of the Chain Deformation Problem

Go and Scheraga have given a general solution for determining the possible conformations of a section of a flexible polymeric chain between two fixed bonds (if the bonds coincide, the problem is equivalent to ring closure). Often, the fixed bonds are related by symmetry, such as that imposed by helicity or folding of antiparallel chains. A technique is shown for obtaining solutions using interactive computer graphics, whereby a plausible chain conformation or fold is approximated manually and completed by mathematical minimization. The procedure allows rapid, repetitive exploration of multiple solutions, and has many options for changing constraints. As an example, the backbone conformation of GpC, a dinucleoside phosphate, is used as a starting model, and gives upon minimization a set of backbone angles in the range of 11-fold helical RNA

Confounding

The magnitude of confounding is examined in nine case studies of two "weak" relationships: between artificial sweeteners and bladder cancer, and between oral contraceptives and cervical dysplasia. Confounding had little or no influence on the results of any published study. The responsible epidemiologist must always consider the possibility of confounding, no less when associations are weak than when they are strong. Identification of potentially confounding variables is an integral part of good epidemiologic practice. Rarely, however, does confounding itself, especially from unidentified sources, live up to its reputation for introducing seriously spurious associations. An investigator is more likely to be led astray by undetected biases than by pure confounding

Are Babies Normal

Clemons and Pagano suggested that certain anomalies in the distribution of birth weights are an artifact of digit bias arising when some hospitals report weight in grams and others in pounds and ounces. In this letter I report yet another administrative source of bias in New York City reports of low birthweight, namely, under-reporting of short-lived infants by hospital staff with incomplete knowledge of Health Code requirements. These infant deaths are often identified by NYC Department of Health inspection of medical records in selected hospitals known to have many high-risk births

Exposure Opportunity Models for Agent Orange, Dioxin, and Other Military Herbicides Used in Vietnam, 1961–1971

Nearly 19.5 million gallons of herbicides were sprayed on the Republic of Vietnam between 1961 and 1971 for military purposes. Amounts of spray and patterns of applications are available in an electronic file called HERBS that contains records of 9141 defoliation missions, including detailed coordinates of US Air Force Ranch Hand aircraft flight paths, along with chemical agent and gallonage sprayed. Two classes of models for use in epidemiological and environmental studies that utilize the HERBS data for estimating relative exposure opportunity indices are presented: a discrete "hits" model that counts instances of proximity in time and space to known herbicide applications, and a continuous exposure opportunity index, E4, that takes into account type and amount of herbicide sprayed, distance from spray application, and time interval when exposure may have occurred. Both direct spraying and indirect exposure to herbicide (or dioxin) that may have remained in the local environment are considered, using a conservative first-order model for environmental disappearance. A correction factor for dermal versus respiratory routes of entry has been incorporated. E4 has a log-normal distribution that spans six orders of magnitude, thus providing a substantial amount of discrimination between sprayed and unsprayed areas. The models improve on earlier ones by making full use of the geometry of the HERBS spray flight paths of Ranch Hand aircraft. To the extent possible so many decades after the War, the models have been qualitatively validated by comparison with recent dioxin soil and biota samples from heavily contaminated areas of Vietnam, and quantitatively validated against adipose dioxin obtained in epidemiological studies of Vietnamese. These models are incorporated within a geographic information system (GIS) that may be used, as one would expect, to identify locations such as hamlets, villages, and military installations sprayed by herbicide. In a novel application, the GIS also facilitates quantitative risk assessment in epidemiological and ecological studies by applying the models within a framework of historical reconstruction of exposure history of individuals based upon their location histories