Background: The epidemics of severe acute respiratory syndrome (SARS) in Hong Kong generates the need to evaluate the effectiveness of control measures. Hong Kong is a densely populated international city with strong communication links between residents which facilitate the rapid spread of infectious diseases. In the early phase of outbreaks, contact tracing followed by quarantine or isolation is an important infection control measure. However, it may not be achievable to trace all contacts with limited resources in a short period of time. Given that resources were top stretched to the limit over a short period of time in early phase of outbreak, resources need to be prioritized and allocated to trace number of identified physical contacts.
Methods and materials: An individual-based mathematical model was developed alongside a resource-constrained contact tracing process for SARS outbreak. We assumed that the outbreak is uncontrolled if the cumulative number of severe/death cases is more than the number of intensive care unit beds in Hong Kong. This simulation environment was tested in scenarios that reflect both actual uncertainties of SARS. We estimate the likelihood to control the outbreak by varying (1) the maximum number of individuals to be traced (2) the proportion successfully to be traced (3) start time to implement the contact tracing since the start of the epidemic.
Results: Given 100% of contacts traced and duration of quarantine of 2 days, varying the resources for the maximum daily number of contacts traced from unlimited to one, the latest start time to implement the contact tracing since the start of the epidemics to ensure at least 95% confidence to control the disease changed from Day 22 to Day 12. Reduction of successful contacts traced to 50% with unlimited resources, the probability of disease containment dropped substantially to ∼28% if contact tracing still started on day 22. Contact tracing was shown to be ineffective if only 1 contact was traced per day with 50% proportion successfully to be traced.
Conclusion: An improved understanding of the transmission dynamics of the SARS outbreak under different scenarios of contact tracing approach helps design the optimal control strategies with the given resources to control new emerging disease in the future.