The pandemic of COVID-19 caused by a novel corona virus now known as SARS CoV-2 which started in Wuhan, China in December 2019 has to date (April 29, 2020) infected more than three million people worldwide with over 227,000 fatalities. Despite rapid identification and sequencing of SARS CoV-2, the origin and mode of transmission of this virus has not been fully elucidated. At the start of the epidemic, it was suggested that bats might be the primary host and wild animals sold in the Wuhan Huanan Seafood Market could be intermediate hosts of the virus. Subsequent epidemiologic studies did not support the market as the origin and sole source of the outbreak. Detailed examination of the timeline of the epidemic suggests that sewer rats might be an important intermediate host between bats and humans. This hypothesis is parsimonious with current observations and can explain in part the limited success of containing the epidemic in Wuhan with strict quarantine of its human population.