The importance of bioaerosols in hospital infections and the potential for control using germicidal ultraviolet irradiation

In recent years a number of factors have stimulated an increased awareness of the presence of potentially pathogenic bioaerosols in indoor and outdoor environments and the detrimental health effects associated with them. The incidence of hospital acquired infection is a serious and widespread problem, with an estimated 1 in 10 patients acquiring an infection during a hospital stay. There are a whole range of potentially pathogenic microorganisms associated with nosocomial infections many of which are opportunistic pathogens which frequently cause respiratory infections particularly in immunocompromised patients. In order to determine the extent of the problem it may be necessary to carry out sampling in order to verify and quantify the presence of bioaerosols in the air. There are a large number of different air samplers available and the choice of sampler type will be highly dependent upon the location in which the sample is to be taken and the information required. In sensitive locations such as hospitals the primary consideration may be the need to cause as little disturbance to the patients as possible. Once an airborne route of infection has been identified as a transmission route there are several possible control strategies available including the use of germicidal ultraviolet disinfection. In the USA in particular ultraviolet disinfection systems are currently widely used in hospitals and other health care environments in order to protect patients and healthcare workers. Microorganisms are particularly vulnerable to UV light at wavelengths close to 254nm since this represents the maximum absorption wavelength of their DNA molecule. Photons of UV light strike a biological cell and the energy is absorbed by nucleic acids in the DNA molecule leading to the formation of pyrimidine dimers and other lethal photoproducts. The formation of pyrimadine dimers leads to changes to the double helix structure, cell mutation and ultimately to the death of the cell. Research carried out at the University of Leeds and elsewhere has shown that a whole range of potentially pathogenic bacterial species are susceptible to UV. It has also highlighted the importance of environmental factors such as relative humidity and the positive effect high levels of relative humidity can have on the survival of bacteria after UV exposure. Although history shows that the uptake of UV disinfection has progressed slowly the future looks extremely promising. With increasing concerns over rising numbers of TB outbreaks, new pathogens such as SARS and avian flu and also the increased risk of bioterrorism threats the market for new disinfection technologies is great. In addition to clinical applications, this technology would also be similarly applicable to waste management facilities for controlling potential pathogens such as Aspergillus fumigatus.