Disease surveillance during a large religious mass gathering in India: The Prayagraj Kumbh 2019 experience.

Background: Mass gathering (MG) events are associated with public health risks. During the period January 14 to March 4, 2019, Kumbh Mela in Prayagraj, India was attended by an estimated 120 million visitors. An onsite disease surveillance was established to identify and respond to disease outbreaks.