Study on the interzonal migration of airborne infectious particles in an isolation ward using benign bacteria.

UNLABELLED: Negative pressure isolation wards are essential infection control facilities against airborne transmissible diseases. Airborne infectious particles are supposed to be contained in the isolation room. However, negative pressure may break down by door-opening action or by human movement. Understanding the interzonal transport of airborne infectious particles in the isolation wards can aid the design and operation strategy of isolation facilities. In this work, the interzonal migration of airborne infectious particles by human movement was studied experimentally in an isolation ward. Artificial saliva solution with benign E. coli bacteria was aerosolized to simulate bacterium-laden infectious particles. The interzonal migration of aerosolized bacteria was characterized by biological air sampling. Less than 1% of airborne infectious particles were transported to the higher pressure zone when door was closed. With human movement, 2.7% of the particles were transported from the anteroom to the corridor. From high-to-low pressure zones, as much as 20.7% of airborne infectious particles were migrated. Only a minimal amount of particles was transported from the corridor to the positive pressure nurses' station. Infection risk of tuberculosis of the healthcare workers and other occupants in the isolation wards were also assessed based on the measured migration ratios. PRACTICAL IMPLICATIONS: Human movement is an important factor governing interzonal migration. It is the main cause of migration of airborne infectious particles to a relatively negative pressure zone. This study provides a set of experimentally obtained particle migration ratios by human movement. Other than serving as empirical data for further studies on the mechanics, these migration ratios can also be used to assess the infection risk for occupants in the isolation ward.

A methodology for estimating airborne virus exposures in indoor environments using the spatial distribution of expiratory aerosols and virus viability characteristics.

UNLABELLED: This study investigated the feasibility of using the spatial distribution of expiratory aerosols and the viability functions of airborne viruses to estimate exposures to airborne viruses in an indoor environment under imperfectly mixed condition. A method adopting this approach was tested in an air-conditioned hospital ward. Artificial coughs were produced by aerosolizing a simulated respiratory fluid containing a known concentration of benign bacteriophage. The bacteriophage exposures estimated on the basis of the spatial aerosol distributions and its viability function were in reasonable agreement with those measured directly by biological air sampling and culturing. The ventilation flow and coughing orientation were found to play significant roles in aerosol transport, leading to different spatial distribution patterns in bacteriophage exposure. Bacteriophage exposures decreased with lateral distance from the infector when the infector coughed vertically upward. In contrast, exposures were constant or even increased with distance in the case of lateral coughing. The possibility of incorporating the proposed exposure estimation into a dose-response model for infection risk assessment was discussed. The study has also demonstrated the potential application of viability functions of airborne viral pathogens in exposure assessment and infection risk analysis, which are often unavailable in literature for some important communicable diseases. PRACTICAL IMPLICATIONS: The proposed method makes use of the viability function of the virus and the spatial distribution of the expiratory aerosols for virus exposure estimation. Spatial differences in aerosol distribution and its influences on virus exposure in an air space can be determined. Variations in infectious dose with carrier aerosol size could also be considered. The proposed method may serve as a tool for further investigation of ventilation design and infection control in clinical or other indoor environments.

Optimising antimicrobial prescription in hospitals by introducing an antimicrobial stewardship programme in Hong Kong: consensus statement.

OBJECTIVE: To discuss the implementation of an 'antimicrobial stewardship programme' as a means to improve the quality of antimicrobial use in a hospital setting in Hong Kong. PARTICIPANTS: Consensus working group on 'antimicrobial stewardship programme', The Scientific Committee on Infection Control, Centre for Health Protection, Department of Health, comprised 11 experts. The remit of the working group was to discuss the rationale and requirement for optimising antimicrobial prescriptions in hospitals by the introduction of an 'antimicrobial stewardship programme'. EVIDENCE: PubMed articles, national and international guidelines, and abstracts of international meetings published between January 2000 and December 2004 on programmes for improving the use of antimicrobials in hospitals. Only English medical literature was reviewed. CONSENSUS PROCESS: Data search was performed independently by three members of the working group. They met on three occasions before the meeting to discuss all collected articles. A final draft was circulated to the working group before a meeting on 3 January 2005. Five commonly asked questions about an 'antimicrobial stewardship programme' were selected for discussion by the participants. Published information on the rationale, components, outcome measures, advantages, and disadvantages of the programme was reviewed. Recent unpublished data from local studies of an 'antimicrobial stewardship programme' were also discussed. The timing, potential problems, and practical issues involved in the implementation of an 'antimicrobial stewardship programme' in Hong Kong were then considered. The consensus statement was circulated to and approved by all participants. CONCLUSION: The continuous indiscriminate and excessive use of antimicrobial agents promotes the emergence of antibiotic-resistant organisms. Antimicrobial resistance substantially raises already-rising health care costs and increases patient morbidity and mortality. Pattern of prescriptions in hospitals can be improved through the implementation of an 'antimicrobial stewardship programme'. A 'universal' and 'continuous' 'antimicrobial stewardship programme' should now be established in Hong Kong hospitals.