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The purpose of this study is to determine to what extent the house-dust mite is sensitive to commercially available chemical substances which could be expected to show a killing effect on the mite. Not only phytopharmaceutical agents with a known acaricidal activity, but also commonly used insecticides and disinfectants have been screened for miticidal properties. The results of the study show that the insecticides and disinfectants which have been tested here showed a negligible effect. Only Lindane effectively kills the house-dust mite when it is used in a concentration of 1 per cent.

The first publication on testing disinfection procedures dates back to 1881 and was compiled by Robert Koch. Although his conclusions were erroneous, we continue to use the "germ carrier test" right up to the present day even if preference is now given to the suspension test first devised by Geppert. Over the years many conceptual milestones had to be reached, and much knowledge and many insights were needed to develop this procedure further to ensure reproducible results. Today, the disinfectant effect is calculated in terms of logarithmic reduction factors for the microbial count: a reduction of 5 log levels has been agreed, i.e. an inactivation kinetics of 99.999%.Of paramount importance was, in particular, the insight that different methods had to be employed to test disinfectants, while doing so not only in the laboratory but also under everyday working conditions. This gave rise to a situation whereby each country developed its own test methods, producing significantly different results. It was only in 1970 that the parties concerned came together so as to reach a uniform solution in Europe. The achievements of the "International Colloquium" were later adopted and continued by the European Standardization Committee (CEN) in a special working group (TS 216). The most important accomplishment of this working group is, no doubt, the insight that it is not a testresult but rather a testsystem that will reveal the truth. The tests carried out in Phase 1 are quantitative suspension tests to elucidate the bactericidal, virucidal, tuberculocidal, fungicidal and sporicidal efficacy. Phase 2 defines the requisite concentration per exposure time. CEN was founded and is sponsored by industry, since the latter needs reliable standards. Time will tell whether this was not perhaps the greatest milestone in the development of test methods. However, the successes scored by CEN are ultimately only the logical consequence of the accomplishments already achieved by the "International Colloquium". In reality, most of the procedures that today have been accepted via TS 216 are based on the activities set in motion by the Colloquium. It is impossible to acknowledge just how pivotal was the role played by both legendary "International Colloquia" in 1970 and 1972 in Hamburg in the development of uniform test procedures.

Besides an atraumatic procedure, aseptic techniques during surgery have been suggested to have a positive impact on the predictability of osseointegration. To avoid an infection of the surgical field, coverage of the face of the patient (drapes) and nose (surgical mask, drape and plastic film) were advocated in order to reduce airborne infections and to prevent a contact contamination of instruments and gloves. Such a coverage, however, increases the feeling of claustrophobia when local anaesthesia is used and can lead to hypoxemia. The aim of the present study was to investigate whether the expired air via the nostrils could contribute to the contamination of the oral surgical field. Test blood agar plates were installed for 30 min under the nose of volunteers lying on a surgical table; once with full coverage of their nostrils, as indicated above, and once without. Simultaneously, control plates were installed on a table besides the patient to measure the basic contamination from the environment. All plates were incubated both aerobically and anaerobically. The number of colony forming units (c.f.u.) recorded on test plates after aerobic and anaerobic incubation were surprisingly low, with a mean score of 2.7 and 5.0 c.f.u. for the uncovered situation, and 2.5 and 3.3 c.f.u. for the covered situation, respectively. The control plates were infected by a nearly comparable number of bacteria (means ranging from 2.2 to 3.2). These findings indicate that covering nostrils by a mask and sterile adhesive plastic film is not essential in avoiding airborne microbial contamination. However, the use of a meshed nose guard to prevent contact with the highly contaminated nasal skin is highly recommended.

The situation of hospital hygiene in Belgium and in the Netherlands is described in the light of the official regulations, the composition and the functioning of the infection committee and of the hospital hygiene team, and the availability of official or semi-official guidelines. Typical for the Netherlands in the long tradition of issuing guidelines on hospital hygiene, in the beginning in 1966 in the form of an advice of the Health Council, at present in the guidelines of the Working Group on Infection Prevention (WIP). A particularity for Belgium is the financing by the state of the hospital hygiene doctor and the hospital hygiene nurses based on a system of scores in which the beds of specialisms with a higher infection risk count for more than general beds.

The AOAC use-dilution method was applied in order to assess the bactericidal activity of 29 commercial preparations for surface disinfection and the Kelsey-Sykes test under clean conditions for 38 preparations. The results of both tests are compared with those of the in vitro test (with the disinfectant diluted in distilled water, in water of standardized hardness, and in a 0.2% albumin solution), those of the European suspension test under clean and under dirty conditions, and those of four practical tests (the AFNOR test, the DGHM test, the QCT and the QSDT). Both the AOAC use-dilution method and the Kelsey-Sykes test under clean conditions are more severe than the suspension tests and, in the case of Pseudomonas aeruginosa, even than most practical tests. The results of both tests correlate well to one another, and to the results of in vitro test, but less to those of the European suspension test. For the practical tests the correlation depends on the testing technique and on the test organism.

The objective of this study is to determine to what extent the value of a preparation for surface disinfection in practice can be predicted by the usual tests, namely the in vitro test in which the disinfectant is diluted in distilled water, in water of standardized hardness or in a 0.2% albumin solution, the European suspension test under clean and under dirty conditions, The Kelsey-Sykes test under clean conditions, the AOAC use-dilution method, the practical tests of the AFNOR, of the DGHM, the quantitative carrier test QCT and the quantitative surface disinfection test QSDT. Therefore the results of all these tests are compared to the ranking order of the efficacy of the same preparations in practice tests, in which slides contaminated with stool or infected urine are disinfected. There is no correlation between the results of the suspension tests and those of the practice tests, but the practical tests (DGHM test, QCT and QSDT) correlate well with practice. Practical tests (second stage of the testing schedule) are therefore necessary for the evaluation of surface disinfectants, as suspension tests alone will not suffice.

The results of the testing of 38 preparations intended for surface disinfection are compared in order to evaluate the value of the suspension tests. The studied testing methods are: the in vitro test (IVT) with the disinfectant diluted in distilled water (AD), in standard hard water (WSH) and in 0.2% albumin; the European Suspension Test (EST) under clean and under dirty conditions; the French AFNOR test NF T 72-190; the practical test of the German Society for Hygiene and Microbiology (DGHM); and the Quantitative Surface Disinfection Test (QSDT). The suspension tests yield comparable results (Table 1). These results correlate very well with these of the AFNOR test, to a lesser extent with those of the DGHM test and hardly with the results of the QSDT, which is the most real-life mimicking practical test (Table 2). Suspension tests are not able to exclude only inactive preparations from further testing in practical tests: they are not specific (Tables 3 and 4). Therefore, it is necessary to include practical tests in the testing schedule for the evaluation of the bactericidal activity of surface disinfectants.