Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: Polio Lab Leak Caught with Wastewater Sampling, published by Cullen on April 7, 2023 on The Effective Altruism Forum. I hadn't seen this discussed here: The near complete eradication of wildtype polioviruses (WPV) means that strict containment by facilities for essential work with infectious WPV is required. In the Netherlands, we have implemented environmental surveillance around all poliovirus essential facilities (PEFs) premises to monitor possible breaches of containment. After the isolation and identification of WPV3 Saukett G strain in a sewage sample collected on 15 November 2022 by the National Polio Laboratory (NPL) in the Netherlands, an immediate response was required to assess any possible ongoing WPV3 shedding and mitigate the risk. Here we describe this response, including the isolation of WPV3 in a sewage sample, and identification, isolation and monitoring, as well as tracing of contacts of an infected employee. Thanks for listening. To help us out with The Nonlinear Library or to learn more, please visit nonlinear.org.