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Biomedical subjects

H G ten Dam

Publications and source records attributed to H G ten Dam.

At least 19 recordsLinked to original sources
PubMed1989

Tuberculosis control in refugee settlements.

Tuberculosis and its management in refugees and other displaced persons in temporary settlements poses a challenge to organisations coordinating and providing care in refugee emergencies. This paper offers a consensus of the co-sponsoring agencies on practical recommendations for implementing measures aimed at both interrupting transmission of tuberculosis and treatment of individual patients.

Humans↗
PubMed1988

Evaluation of the effectiveness of BCG vaccination using the case-control method in Buenos Aires, Argentina.

A retrospective case-control study was conducted in Argentina to determine the protection conferred by BCG vaccination against tuberculosis in children under six years of age, in an area where coverage is about 55%. A total of 175 tuberculosis patients were included. Five controls selected from patients treated at the same hospital as those under study for reasons other than tuberculosis were matched to each case on the basis of age, socioeconomic origin, nutritional status and place of residence. Information on BCG vaccination status was collected by an independent examiner. Tuberculosis localizations were as follows: 152 pulmonary, pleural and/or miliary; 18 meningitis; 2 lymphadenitis; 2 osteoarticular; and 1 otic. The diagnosis was based on bacteriological and histopathological tests, computerized tomography, radiology, clinical examination, endoscopy, and proved source of infection. The protective effect of BCG among those who were vaccinated was 73.0% with 95% confidence limits of 82% and 62%. According to these results BCG vaccination given early in life is very effective in preventing tuberculosis.

Argentina↗
PubMed1986

The protective effect of BCG vaccination of the newborn against childhood tuberculosis in an African community.

The latest controlled trial of BCG vaccination in southern India showed that two vaccines failed to confer protection against pulmonary tuberculosis. This result cast serious doubt on the effectiveness of BCG vaccination of the newborn, which is widely applied in developing countries. Therefore, WHO initiated a global research study to evaluate current programmes in developing countries. Part of this study was carried out in Lomé, Togo, in which child contacts of newly detected patients were followed up with clinical and radiological examinations. All observations were recorded according to a scoring system. Concomitant observations were made to verify the comparability of the vaccinated and unvaccinated children. Of the child contacts of 352 index cases, 1421 completed the examinations. The distribution of the final score made it possible to distinguish 175 children likely to suffer from tuberculosis: 113 among the 546 unvaccinated and 62 among the 875 vaccinated children. Significant incomparability was observed in respect of intensity of exposure: the vaccination coverage was relatively low, and the risk of disease relatively high, if a parent was the index case or the child shared the bedroom of the index case (which very often coincided). The other variables studied, including age and sex, turned out to be practically irrelevant as regards comparability. The estimate of the protective effect against all types of tuberculosis combined is 61.5%, which is slightly lower than suggested by the raw data (66%). The protective effect, however, appeared to increase considerably with severity of disease. In children of 5 years and older it was lower than in the younger children. Tuberculin testing failed to reveal any sensitivity induced by BCG in the vaccinated children. The distribution of the tuberculin reactions correlated poorly with the other diagnostic findings. Small reactions were only slightly more frequent in healthy than in sick children; only the very large reactions were associated with a higher risk of disease. This confirms that the tuberculin test is of very limited diagnostic value in young children.

BCG Vaccine↗
PubMed1984

Research on BCG vaccination.

BCG vaccination against tuberculosis has been used for many years in practically all national tuberculosis programmes. It is often the mainstay of the programme as regards young children, in whom case-finding and treatment remain deficient, especially regarding the serious meningeal and miliary forms of tuberculosis. Following contradictory reports on the effectiveness of BCG vaccination, a large-scale controlled trial was carried out in south India, under the sponsorship of WHO. The early results of this trial showed that BCG vaccination provided no protection whatsoever against bacillary disease in adults. To examine this unexpected finding WHO convened a Scientific Group, which considered that the reported results per se are valid but might not apply in general. Since the effectiveness of a potentially very useful and generally applied control measure appeared seriously challenged, a Study Group was convened by WHO. The Group considered that under the circumstances BCG vaccination, especially of young children, should be continued, but that the effectiveness of BCG vaccination should be evaluated forthwith. A comprehensive programme has been formulated accordingly. The primary objective of the programme is to evaluate in an expedient manner the effectiveness of BCG vaccination in children. A number of problems inherent to the special situation had to be circumvented. In the case of tuberculosis, community trials of the classical type have to be prolonged and are extremely costly. Moreover, since BCG vaccination has been used widely, it is virtually impossible to find a suitable trial area; many countries are reluctant to conduct such trials for ethical reasons because they require an unvaccinated group. Retrospective studies, although providing no conclusive scientific evidence when carried out in isolation, may give useful information if organized in a comprehensive evaluation programme. Another approach proposed is based on the active follow-up of child contacts of newly detected cases of tuberculosis. This provides information on the magnitude of the tuberculosis problem in children as well as a powerful retrospective evaluation of the protective effect of vaccination; in the case that the results are inconclusive a prospective approach on the same principle would be ethically justified. The study population is only a small fraction of that required in a community trial, and the follow-up of each individual is reduced to a few months. In addition to providing information on the effectiveness of BCG vaccination, the field studies, supported by other research, may clarify the variations in protection observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1982

Pathogenesis of tuberculosis and effectiveness of BCG vaccination.

Among the hypotheses offered to explain the conflicting results of various trials of BCG vaccination, the one invoking gross differences in the immunogenic properties of the various BCG vaccines (strains) has received most attention. Indeed, for many years research in BCG vaccination has been directed almost entirely towards improving the quality of vaccines. the anticipated benefit of this work, however, is not borne out by the results of the latest trial in India. Whereas it cannot be excluded that technological advances may have resulted in the worst vaccines ever, it also remains possible that the basic hypothesis was less relevant than presumed. the quality of the vaccine may be of little importance and a different explanation should be sought for the observed differences in protection. One possible lead is the observation that BCG vaccination consistently appeared to be of poor efficacy under conditions where, in a vaccination programme, even an effective vaccine would have little impact on the tuberculosis problem, i.e. where the majority of cases originated from the population already infected. The hypothesis offered is that in such populations the pathogenesis of tuberculosis is different from that prevailing under the clearly exceptional conditions under which BCG vaccination was effective. Rather than being the direct result of primary infection, tuberculous disease (observed) may be the result of reinfection. In this case BCG vaccination cannot be expected to have a protective effect.

Adolescent↗
PubMed1980

Determining the prevalence of tuberculosis infection in populations with non-specific tuberculin sensitivity.

In tropical countries, where there is generally a high prevalence of non-specific sensitivity, the tuberculin test is inadequate for detecting tuberculosis infection. A method is proposed by which the prevalence of infection in the population can be determined under such circumstances thus making possible meaningful epidemiological surveillance of the disease. This method compares levels of tuberculin sensitivity in individuals before and after BCG vaccination. If BCG vaccination fails to produce an increase in tuberculin sensitivity, the individual must have been infected with human or bovine tubercle bacilli.

Africa↗
PubMed1977

BCG vaccination by bifurcated needle in a pilot vaccination programme.

The bifurcated needle technique for BCG vaccination was compared with intradermal injection in a mass BCG and smallpox vaccination programme in Afghanistan. In all population groups the bifurcated needle technique produced substantial tuberculin sensitivity, which however was significantly inferior to that following intradermal injection. The advantages of the bifurcated needle technique did not result in a significant increase in vaccination coverage and output. Under the present circumstances vaccination by bifurcated needle would probably be more expensive than intradermal vaccination.

Adolescent↗
PubMed1970

The use of jet-injectors in BCG vaccination.

In mass vaccination programmes, the jet-injection of vaccine may have considerable operational advantages over the classical techniques. The technical performance of two models of jet-injector, the Dermo-Jet and the Ped-O-Jet, in BCG vaccination was assessed in a number of studies which are reviewed by the authors. It is shown that the jet-injectors do not administer the full dose for which they are calibrated and that the size of the vaccination lesion varies more than after vaccination by syringe.By increasing the dosage considerably, the results of vaccination by jet-injection may be improved to a certain extent but the risk of unpleasant reactions is also increased.

BCG Vaccine↗
PubMed1969

Epidemiological significance of the local reaction to direct BCG vaccination as assessed from a study in Mongolia.

Direct BCG vaccination has considerable operational advantages over the classical method of vaccinating only persons who do not react to tuberculin. In the present study it is shown that the direct method as applied in Mongolia does not cause any untoward reactions in persons who react to tuberculin and therefore can be considered a rational public health procedure.By reason of the repeated follow-up examinations, it was possible to obtain a clear picture of the development of the local BCG reactions and to test the hypothesis that these reactions may give information on pre-existing tuberculin sensitivity. It appeared impossible to deduce with any accuracy from either the local induration or the tissue destruction at the site of vaccination whether a person had tuberculin sensitivity before vaccination or not, and the results obtained with 2 different vaccines were inconsistent. It is therefore concluded that the local BCG reaction has no epidemiological significance in this respect.

Adolescent↗