HYMS RESEARCH PROFILE

Airborne spread of infection in hospitals - Professor Kevin Kerr

Kevin Kerr, Consultant Microbiologist and Director of Infection Prevention and Control for Harrogate and District NHS Foundation Trust, was appointed HYMS Honorary Clinical Professor of Microbiology in 2003. His principal research interest concerns engineering-based interventions to interrupt the spread of infection. One topic in this field is the airborne route of transmission of infection.

THE foot and mouth epidemic of 2001 and the threat of the deliberate release of infectious agents into the air in acts of bioterrorism have focused attention on the airborne route of infection. However, apart from a few exceptions, airborne transmission has long been considered relatively unimportant for healthcare-associated infection.

Professor Kerr, along with collaborators at the School of Civil Engineering at the University of Leeds and the School of Design Engineering and Technology at the University of Bradford, has been reassessing the importance of the airborne spread of infection in hospitals.

Early studies, which were funded by NHS Estates, looked at ultraviolet irradiation to remove microorganisms from the air but yielded disappointing results - mainly because of the difficulty of ensuring that airborne bacteria are exposed to lethal doses of irradiation.

He secured funds to build a purpose-designed aerobiological test chamber RESEARCH 6 (about the same size as a hospital ward side room) and computational fluid dynamic (CFD) analysis of data from the chamber revealed that, even under relatively simple conditions, the path of microorganisms in the air is extremely complex, underlining the difficulties in killing them through exposure to a UV source.

A bid to the Engineering and Physical Sciences Council (EPSRC) to investigate further the behaviour of microorganisms in the air and factors influencing their susceptibility to UV light was successful with some of the work published in the Journal of Aerosol Science.

He sought an alternative to UV irradiation in the form of negative air ionisation. This technology was evaluated in an NHS Estates-funded study on an intensive care unit in which the multiplyantibiotic resistant nosocomial pathogen, Acinetobacter baumanii, was endemic and had proved refractory to conventional infection control interventions. There was a statistically significant reduction in infections when the ionisers were in use and the results, published in Intensive Care Medicine, were also reported in the national media. Data from the study, however, contradicted the accepted explanation as to how ions remove microorganisms from the air and a large project grant (£280,000) from the EPSRC supported further investigations into the effects of negative ions on the behaviour of airborne bacteria.

Other on-going projects, some of which are funded by commercial partners, include investigating the role of airborne transmission in the spread of norovirus and Clostridium difficile infection.

In addition, the team has discovered that bacteria in the air carry an overall electrical charge and is considering the implications of this for the clinical environment – for example a plastic apron pulled off a dispenser by a nurse before attending to a patient generates a static potential on the apron of up to 5kV and this will repel similarly charged bacteria in the air towards the patient.

September 2006

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