Transmission of Infectious Bioaerosols - Sources, transport and prevention strategies for airborne viruses and bacteria

Infectious diseases that can be transmitted via air often spread rapidly, sometimes causing large epidemic and pandemic outbreaks. As an increasing number of people live in crowded urban environments, and with frequent and long-distance traveling across the world, infectious diseases can spread even faster. Yet, our knowledge of how much airborne transmission (here defined as aerosol particles <100 μm that contain infectious agents) contributes to the spreading of diseases is scarce and frequently debated. The aim of this thesis was to increase knowledge about the sources and airborne transport of infectious bioaerosols in order to prevent diseases from spreading via air.
To identify possible sources of infectious bioaerosols, we collected air samples in hospitals for detection of bacteria (in operating rooms) and norovirus (in hospital wards) and correlated the results with possible source events. To study bacterial viability and viral infectivity after airborne transport, we developed an experimental setup in the laboratory where aerosolized model organisms were examined. The setup was also used to evaluate the particle collection efficiency of a novel bioaerosol sampler. In addition, three types of high-airflow ventilation systems for operating rooms were compared for their ability to maintain clean air during ongoing surgery.
We detected norovirus RNA in air samples collected in hospitals during outbreaks of the winter vomiting disease. Our results showed a significantly higher risk of finding norovirus RNA in the air within a short time (3 h) after a patient vomited.
The median bacterial concentrations measured in operating rooms ranged from 0 to 22 CFU m^-3 (colony forming units), with the lowest median bacterial concentrations in the ventilation types with the incoming airflow above the operating table, directed downwards.
Experimentally aerosolized murine norovirus in a laboratory study showed that infectious viruses were collected from air, however with reduced infectivity. We proposed that aerosol droplet drying from a low-solute solution caused the loss of viral infectivity. A similar experimental setup, was used to study the viability of Pseudomonas syringae in air with varying levels of relative humidity. The bacterial survival was higher when aerosolized into air with low relative humidity, corresponding to rapid drying.
With this research, I highlight the importance of studying infectious bioaerosols, in particular for nosocomial infections, by showing that sufficient concentrations of bacteria and viruses are present in hospital air that can trigger new infections, and that bacteria and viruses aerosolized under controlled laboratory conditions remain viable and infectious.