This is a reference to a plague outbreak in Iraq in 131 AH. Hossein Modarressi cites this reference as an example of the importance of employing external evidence (such as corroborating dates for historical events that appear in various sources) with respect to the use of materials attributed to or about Jaʿfar al-Ṣādiq.
This source is part of the Online Companion to Hossein Modarressi, Text and Interpretation: Imam Jaʿfar al-Ṣādiq and His Legacy in Islamic Law (Harvard University Press, 2022).