M. A. EL BATAWI (World Health Organization, Geneva, Switzerland): The opening presentation made an attempt at defining occupational disease. The World Health Organization has published a book on the interaction between work and health demonstrating the different levels at which work may influence health. For example, the occupational disease of lead poisoning cannot be caused by carbon monoxide; it has to be caused by lead exposure. That is a causeleffect relationship-one cause, one effect. Other such relationships include carbon monoxidecarboxyhemoglobin, asbestos-asbestosis, and silica-silicosis. These can be called the “hundred percent” relationships. Beyond those few relatively straightforward examples, however, we consider many of the diseases that affect the working population and human beings as a continuum: a person has his work; he interacts with so many pollutants in food and air and water; he undergoes stress at work and stress at home; and all these things add up to the well-named diseases of multifactorial causes. Now, I am distinguishing between the terms “occupational” and “work-related,’’ which implies a partial relatedness. Here we do not find causes, we find risk factors. And there is a difference between a cause and a risk factor. For example, if you discuss chronic obstructive pulmonary disease (COPD) or occupational asthma, smoking plays a very important role in causation as does pollution in the work environment and irritants from the atmosphere. Multiple factors play a role in COPD, yet when you diagnose a case of chronic obstructive pulmonary disease in a person exposed to dust, you are faced with the question of compensation. Do you compensate this person and declare the condition an occupational disease? Or is the disease only partly work-related? To what extent is it related to occupation? Epidemiologists are facing a crucial and a very important matter in assessing the role that work may play in the causation of such general diseases as the low back pain syndrome, hypertension, cardiovascular diseases, and stress-related conditions. Unless you consider the person in his or her totality, you will never be able to pin down the causative factors or the risk factors towards which you aim to direct the control measures. IRVING J. SELIKOFF (Mt . Sinai School of Medicine, New York, N . Y . ) : Dr. Fowler, of the 100,000 or so workers now in these high-tech industries, have baseline surveillance mechanisms been set up to see what the problems are going to be? BRUCE A. FOWLER (University of Maryland Medical School, Baltimore, Md. ) : There is a great concern in the semi-conductor industry about these issues. They are moving very rapidly in the direction of setting up good surveillance procedures. In this case, it is the large manufacturing companies that are very concerned about their workers, who represent a highly trained work force, and it is in everyone’s best interest that these workers be maintained in the best of health. However, the greater concern is with the smaller companies, those with fewer than 50 or 100 employees. These workers may not get enough attention and may fall through the cracks of a surveillance system that is being set up mainly by the larger companies. MORTON CORN (The Johns Hopkins University, Baltimore, Md. ) : As you may know, at the Johns Hopkins School of Hygiene and Public Health we have designed and proposed epidemiologic studies for certain of the larger semiconductor companies. I would not want the impression to be left that the exposures in that industry at the leading edge of chip manufacture are of a magnitude that would

D. G. FP. EDWARD (Wellcome Research Laboratories, Beckenham, Kent, England): Ever since the first isolation of organisms of the pleuropneumonia group from the human genital tract, great interest has been taken in their relationship to infection. There would seem to be little doubt that the organisms can be pathogenic for man. Their pathogenicity would appear to be similar to that of Escherichia coli, which is a normal inhabitant of the gut, yet can produce a pyogenic infection if it gains access to other parts of the body. There seems little doubt that organisms of the pleuropneumonia group can cause puerperal fever, salpingitis, and abscesses in the neighborhood of the genital tract. However, in regard to pathogenicity the main question a t issue is whether the organisms are a cause of nongonococcal urethritis. This disease is of great importance and its etiology remains uncertain. Since these organisms are present in a proportion of cases it is tempting to suggest that they cause the infection. Many investigators have studied the relationship of the organisms to nongonococcal urethritis; in various surveys the proportion of positive isolations from cases has varied, but has never exceeded 50 per cent. On the other hand, similar organisms have been isolated from healthy individuals examined as controls. There are differences of opinion as to what constitutes a control group, and doubts have been expressed as to whether the genital tracts of all the controls were completely healthy. Klieneberger-Nobel has examined boys before puberty, but I regard as a control group men from the general population who are not attending a venereal disease clinic. I consider that it is highly significant that a high proportion of these men have Mycoplasma hominis in the urethra. On the other hand the organism can be isolated only from one half or less of the cases of nongonococcal urethritis, although it is not a difficult organism to isolate. There is no difference, clinically or in response to treatment, between cases with positive isolations and those in whom the organism cannot be demonstrated. These findings suggest strongly that M . hominis is not the cause of nongonococcal urethritis. It would appear more likely that it is a commensal, although it is impossible to exclude the possibility that it may produce some ill effects when it gains access to the urethra. It would seem that little can be gained from a repetition of the many surveys already carried out in which the organisms have been sought in diseased and healthy individuals. If the question of pathogenicity is to be decided a new approach must be made. E. A. FREUNDT (Statens Seruminstitut, Copenhagen, Denmark) : I do not think that the different incidence of PPLO in the male urethra found by KlienebergerNobel and by me can be explained by different methods of procuring specimens for cultivation. Actually, the technique I used would not seem to differ essentially from that of Klieneberger-Nobel. My specimens were not taken merely from the “external surface” of the urethral meatus, as supposed by Klieneberger-Nobel, but from the anterior urethra by means of cotton-wool swabs. These were inserted as deep as possible into the urethra after cleaning the meatus with saline. Moreover, I don’t think that the microbial flora of the