Public health response to a tuberculosis cluster in a high-rise apartment block

Objectives: A genetic cluster of eight tuberculosis (TB) cases residing in various units in a single high-rise apartment block in Singapore was detected. A mass screening exercise for active case finding was conducted, and site assessments and simulations were performed to understand potential transmission routes. Methods: All eligible persons were offered screening for TB infection. A site survey was conducted to understand potential environmental factors that might have contributed to the intense transmission, and an airflow model of the block was developed to explore possible mechanisms for inter-unit airborne transmission using computational fluid dynamics simulations. Results: Of 739 persons screened, 212 persons (28.7%) had a positive QuantiFERON Gold Plus test. Of 212 persons with a positive TB infection test, 15 were diagnosed to have TB disease. Of those with a positive culture, six cases were added to the cluster. Computational fluid dynamics simulations suggested that inter-unit transmission could be facilitated in scenarios with a lack of cross ventilation within apartments. Conclusion: The possibility of inter-unit transmission suggests that as with routine TB contact tracing that is based on likelihood of exposure, screening may be expanded based on parameters, such as proximity to the index, infectivity of the index and the attack rate.