Multi-zone modeling of probable SARS virus transmission by airflow between flats in Block E, Amoy Gardens

More than 300 residents of a private high-rise housing estate were infected with severe acute respiratory syndrome within a short period during the 2003 epidemic in Hong Kong. The outbreak occurred after the identified index patient visited a flat on a middle floor in Block E of the Amoy Gardens estate on two nights. Approximately 45% of the subsequently infected people resided in Block E, while the other 55% of infected cases mainly resided in six other blocks close to Block E. The distribution of the infected flats in Block E conformed to a non-uniform spatial pattern. Probable environmental causes for airborne transmission associated with the air movements between flats in Block E are identified. The well-established multi-zone airflow modeling method was used to analyze the virus-laden bio-aerosol dispersion between flats through door and window leakage areas in Block E under six different scenarios. The distribution of infection risk in Block E matched with the virus concentrations in flats predicted with the use of multi-zone modeling. Our study shows the importance of ventilation design in high-rise residential apartments.