| Preventing person-to-person transmission of infectious agents through air is an important part of the agenda in nosocomial infection control practice. This study utilized the traditional bacteriophage recovery technique to establish a cause-effect relation for airborne viral infection in a full-scale general hospital ward, by using benign Escherichia coli ( E. coli) phage (T1) to simulate infectious virus carried on expiratory aerosols, and its host bacterium (E. coli) as the susceptible individual. The expiratory aerosols were artificially simulated by using a tryptone broth as the spraying medium, which has similar dissolved content and mass concentration as sputum. Aerosol size distribution following the literature reported data was used in simulating actual cough events in the experiments. The spatial bacteriophage exposures were estimated by collecting air samples using an Anderson sampler with the host bacterium (E. coli) pre-inoculated on the plate in the sampler. Incorporating with the spatial aerosol distribution measured by an aerosol spectrometer, the bacteriophage viability functions at spatial locations of the ward were estimated. By inputting the measured aerosol data together with literature reported infection dose data of influenza into a cumulative dose model, a spatial distribution of hypothetical airborne viral infection risk was estimated for the ward.The experimental results demonstrated that E. coli phage T1 can withstand the aerosol injection mechanics, but lost about 83% biological viability by dehydration. After a sufficient evaporation (within about 1 seconds), the variation of viability functions were minor in the 6-minute test duration, which was the nominal air turnover rate of the ward. The viability functions obtained at various spatial locations exhibited a location independent characteristic. The ventilation flow pattern played significant roles in the expiratory aerosol transmission, leading to the different exposure distribution patterns in the ward. The measured bacteriophage exposures were in reasonable agreement with those estimated by using aerosol counting data, which reveals the possibility of numerical simulation for further study on airborne diseases transmission. The proposed methodology developed in this research may provide understandings on developing efficient ventilation strategies on the basis of nosocomial infection control practice. |
