This article describes advances in the knowledge of airborne infection in operating rooms since 1867 when Joseph Lister first provided methods of controlling surgical site infection. However, it was not until the mid-20th century that evidence became available to show that airborne microbes were a cause of surgical site infection, and the design of operating rooms was improved to control this route of infection. The contributions from various researchers who investigated the importance of airborne infection and the design of operating rooms are discussed. It was concluded that further progress is still required to fully control airborne infection in operating rooms.

The critical relationship between airborne microbiological contamination in an operating theatre and surgical site infection (SSI) is well known. The aim of this annotation is to explain the scientific basis of using settle plates to audit the quality of air, and to provide information about the practicalities of using them for the purposes of clinical audit. The microbiological quality of the air in most guidance is defined by volumetric sampling, but this method is difficult for surgical departments to use on a routine basis. Settle plate sampling, which mimics the mechanism of deposition of airborne microbes onto open wounds and sterile instruments, is a good alternative method of assessing the quality of the air. Current practice is not to sample the air in an operating theatre during surgery, but to rely on testing the engineering systems which deliver the clean air. This is, however, not good practice and microbiological testing should be carried out routinely during operations as part of clinical audit.

This article discusses the design of unidirectional airflow systems used to ventilate operating theatres and provide low concentrations of airborne micro-organisms during surgical operations. Also described are tests that can be used to confirm that unidirectional airflow systems are well designed and perform correctly when installed and during their lifetime. Reasons are given for the failure of unidirectional airflow systems to provide low concentrations of airborne micro-organisms and reduce joint infection rates after total joint arthroplasty when compared to conventional mixed-airflow operating theatres.

It is necessary to determine locations in a cleanroom where airborne concentrations of particles and microbe-carrying particles (MCPs) should be monitored. It is also necessary to determine the concentrations of airborne contamination that should not be exceeded during manufacturing operations, ie. the alert and action control levels. Both these requirements can be ascertained by simple and informal means. However, should a formal approach be required, the monitoring locations can be determined by a risk assessment, and the control levels by a statistical method. Key Words: Monitoring, airborne particles, control levels, pharmaceutical, cleanrooms

Cleanroom garments are used to control the airborne dispersion of contamination from people into the cleanroom. The effectiveness of the garment in controlling the dispersion of contamination is a function of the fabric and design of garments, and test methods used to ascertain the effectiveness of garments are discussed in this article. These test methods can be used when choosing garments for use in a cleanroom but were used in this article to determine the deterioration of garments through use. Cleanroom garments were subjected to increasing numbers of decontamination cycles, which included sterilisation by gamma radiation, up to a maximum of 70. At defined number of decontamination cycles, the garment’s fabric was compared to a new fabric by visual examination, by a scanning electron microscope, and by physical tests of key performance parameters. It was concluded that the performance of the fabric remained acceptable up to 50 decontamination cycles. This conclusion was supported by the low dispersion rate of particles and microbe-carrying particles in a dispersal chamber from personnel wearing the garments. After 50 decontamination cycles, a low dispersion rate of 0.2/s of microbe-carrying particles from personnel wearing the garments was obtained and a 194-fold reduction in the microbial dispersion rate compared to cleanroom undergarments. Key words: cleanroom garments, garment life, contamination control

The World Health Organization published guidelines in 2016 for preventing surgical site infections. The guidelines contained a conditional recommendation that laminar airflow (LAF) ventilation systems should not be used to reduce the risk of infection after total joint arthroplasty (TJA). This recommendation was largely based on a systematic review and meta-analysis of information from hospital infection surveillance registries. The recommendation contradicts information published in earlier major studies carried out by Charnley and the UK Medical Research Council (MRC). The first aim of this article is to revisit and explain the MRC study, and reply to criticisms of it. The second aim is to suggest reasons why some recent studies have failed to demonstrate that ultraclean air (UCA) systems reduce deep joint infection after TJA. It demonstrates that if a UCA system establishes average airborne concentrations of microbe-carrying particles (MCPs) <10/m3, and preferably <1/m3, then deep joint infection after TJA will be lower than in conventionally ventilated operating theatres.

This paper reports an investigation into the ability of the air supply in non-unidirectional cleanrooms to aid recovery from episodes of airborne contamination, and minimise airborne contamination at important locations. The ISO 14644-3 (2005) recovery test, which measures the rate of decay of test particles, was assessed and a reinterpretation of the test results suggested. This allowed air change effectiveness indices to be calculated and used to evaluate the ventilation effectiveness of the cleanroom's air supply. Air change effectiveness indices were measured in various designs of cleanrooms, and reasons for deviations in the value of the indices investigated.

A sampler that detects and counts viable particles in the air of cleanrooms in real-time was studied. It was found that when the sampler was used to monitor airborne particles dispersed from a number of materials used in cleanrooms, including garments, gloves, and skin, the number of viable particles dispersed from these materials was greater than anticipated. It was concluded that a substantial proportion of these viables were of a non-microbiological origin. When the sampler was used to monitor a non-unidirectional airflow cleanroom occupied by personnel wearing cleanroom garments, it was found that the airborne viable concentrations were unrealistically high and variable in comparison to microbe-carrying particles simultaneously measured with efficient microbial air samplers. These results confirmed previously reported ones obtained from a different real-time sampler. When the real-time sampler was used in a workstation within the same cleanroom, the recorded viables gave results that suggest that the sampler may provide an effective airborne monitoring method, but more investigations are required. LAY ABSTRACT: The airborne concentrations measured by a real-time microbial air sampler within an operational, non-unidirectional airflow cleanroom were found to be unrealistically high due to a substantial numbers of particles of non-microbiological origin. These particles, which resulted in false-positive microbial counts, were found to be associated with a number of materials used in cleanrooms. When the sampler was used within a cleanroom workstation, the counts appeared to be more realistic and suggest that this type of real-time airborne microbial counter may provide a useful monitoring method in such workstations, but further investigations are required.

The redispersion factor of microbe-carrying particles, which is the ratio of the concentration of floor-derived microbes in room air to those on a floor surface, was determined, as was the percentage of floor-derived microbes in room air. These relationships were shown to vary according to conditions in the room. Equations were derived that allow these relationships to be calculated for a variety of room conditions, including air supply rates, levels of personnel activity, and the effect of gravitational deposition on microbe-carrying particles.The redispersion factor in ventilated rooms, such as cleanrooms and operating rooms, when the floor surface concentration was measured by nutrient agar contact dishes, was found to vary from about 1.5 x 10(-4) to 7.4 x 10(-6), and the percentage of floor-derived microbes in room air from about 0.004% to 10.5%. In a typical cleanroom, the redispersion factor is likely to be about 1.0 x 10(-4), and the percentage of floor-derived microbes, 0.7. In a typical operating room, the redispersion factor is likely to be about 5.2 x 10(-6) and the percentage of floor-derived microbes, 2.

The removal efficiency of high efficiency air filters against microbe-carrying particles (MCPs) in the air supply of occupied rooms, such as cleanrooms, was determined. Knowing the size distribution of MCPs in the air to be filtered, and the removal efficiency of a filter against individual particle diameters, the overall removal efficiency was ascertained. A variety of filters were investigated, and it was found that a filter 90% efficient, when tested against sub-micrometre particles, used in standard classification methods such as EN 1822, was greater than 99.99% efficient in removing MCPs. The effect of filter efficiency on the quality of the air supply, and the concentration of MCPs in cleanroom air was also studied. No practical improvement in airborne concentrations was obtained by filters that had a removal efficiency greater than 99.99% against MCPs. Use of a filter suitable for removing MCPs, rather than sub-micrometre particles, would give a reduction of about 6 to 8-fold in the pressure drop over a filter, and a substantial reduction in the cost of running a cleanroom.

Investigations were carried out into the airflow in a non-unidirectional airflow cleanroom and its affect on the local airborne particle cleanliness The main influence was the method of air supply A supply inlet with no diffuser gave a pronounced downward jet flow and low levels of contamination below it, but poorer than average conditions in much of the rest of the room A 4-way diffuser gave much better air mixing and a more even airborne particle concentration throughout the cleanroom Other variables such as air inlet supply velocity, temperature difference between air supply and the room, and the release position of contamination also influenced the local airborne cleanlinessA CFD analysis of airflow fields in a cleanroom was compared with measured values It was considered that a turbulent intensity of 6%, and a hydraulic diameter based on the actual size of the air inlet, should be used for the inlet boundary conditions and, when combined with a k-epsilon standard turbulence model, a reasonable prediction of the airflow and airborne particle concentration was obtained

Air supply volumes and velocities in cleanrooms are monitored by airflow measuring hoods and anemometers but these measuring methods can be inaccurate if used incorrectly. It is demonstrated in this article that measuring hoods are accurate if the air supply passes evenly out of the hood, as occurs when the air volume is measured from a four-way diffuser or no air supply diffuser. However, when a swirl diffuser was investigated, the measuring hood gave readings more than 50% greater than the true volume. The reasons for the inaccuracy, and methods to correct it were established. Vane anemometers give inaccurate readings at the face of high-efficiency air supply filters, and it was found that the most accurate reading was found about 15 cm from the filter face. The number of readings required across the filter face to obtain an accurate average velocity was investigated, as was a scanning method using overlapping passes.

The variables affecting the physical collection efficiency of air samplers of the type that impact microbe-carrying particles onto agar were investigated using a simplified analytical method and computational fluid dynamics. The results from these two techniques were compared, as were the effect of jet velocity, nozzle size, and nozzle distance from the agar surface; also considered was the optimisation of these variables to obtain an efficient design of sampler. A technique is described that calculates the proportion of microbe-carrying particles that a sampler will collect from a typical size distribution of microbe-carrying particles found in an occupied room; the three air samplers studied were found to collect from about 22% to over 99% of the micro-organisms in the room air.

人是洁净室的主要发尘源,因此工人必须穿着无尘服装来降低自身的发尘性.论文列举了三个织物实验,用来测试织物的防尘性能.此外,还介绍了无尘实验室的方法用以测试服装的防尘性能.实验结果说明,孔径在17～103 μm之间的织物对于直径≥0.5 μm的微尘的过滤率在75%之内.发尘室实验显示,紧密织物和无纺布的防尘效率较好.

The use of isolators and barrier technology in pharmaceutical manufacturing may cause design problems, some of them unrecognised. These design problems are highlighted in this paper and, where possible, solutions are given.

The routes of airborne contamination, during Blow-Fill-Seal (BFS) production, were studied using tracer gas, particles and bacteria. The prevention of airborne contamination, by the air shower at the point of fill, was effective (> 99.2% efficient). However, microbe-carrying particles could gain access, by deposition or air exchange, when the containers were cut open and before they shuttled under the protection of the air shower. The use of SF6 tracer gas demonstrated that when the air shower was not on, 50% of the air within the containers came from the area round the machine. When the air shower was switched on, only about 5% of the air came from the surroundings. Airborne microbial contamination of containers is in proportion to: the number of airborne microbes around the machine, the time the container is open, the neck area and the amount of air left within the container. The likely microbial contamination rate can be calculated from a model incorporating these variables. Microbial contamination of containers during BFS manufacturing is normally very low, but by increasing the naturally occurring bacteria in the air of the production rooms by about 100-fold, it was possible to verify the accuracy of this model. The contamination model agrees well with the observation that microbial contamination levels of between 1 in 10(5) and in 10(7) will be found when small containers (< 10 ml) are filled in conventionally ventilated rooms. To achieve similar contamination rates when filling of larger bottles, it is likely that unidirectional flow, or barrier technology will be required.

During pharmaceutical production the quality of the air in manufacturing areas is monitored by volumetric samplers and settle plates. Settle plates are often assigned a secondary role, their usefulness in predicting airborne contamination of containers not being fully recognised. In this paper criticisms of settle plates are answered and the advantages of settle plates explained. It is concluded that using settle plates is the best method of quantifying the likely airborne microbial contamination of containers filled in pharmaceutical production areas.