Risk of tuberculosis transmission by tissue transplantation: a quantitative risk assessment

Two recent tuberculosis outbreaks in the United States implicated a contaminated bone graft product containing living cells. Evidence-based donor selection criteria may help prevent future tragic events like these. However, the development of such criteria must be informed by estimates of the risk of tuberculosis transmission by tissue transplantation, which are currently lacking. Therefore, we aimed to estimate the risk of tuberculosis transmission through tissue transplantation in Québec, Canada. We developed a deterministic model to assess the risk of tuberculosis transmission through the transplantation of skin, cardiovascular, musculoskeletal, and ocular tissues. Transmission risk was estimated according to three scenarios (i.e., most-likely, optimistic, and pessimistic). Except for ocular tissues, the estimated risk was consistently < 1 in 1 million transplantations, even after inflating some parameters by 50% or 100%. In the most-likely scenario, the risk of transmission by ocular tissue transplantation was estimated at only 1 in 312,160. The calculated risk of tuberculosis transmission by tissue transplantation is extremely low in our jurisdiction and does not warrant the implementation of additional risk mitigation measures beyond those currently in place. Albeit low, the estimated risk was higher for ocular grafts in part because they contain living cells, which is not the case of gamma-irradiated tissues. Our work showcases how the selection criteria of tissue donors can be informed by risk estimates derived from mathematical models.