Figure 1.

Date of confirmation of primary cases among cabinmates and secondary transmission on Diamond Princess. Numbers of individuals with infected cabinmates are shown according to the date of the first positive polymerase chain reaction (PCR) result for the primary case (n=266); primary cases were classified as with or without secondary transmission events. Following the onboard quarantine starting on 5 February 2020, and assuming a mean incubation period of 5 days and a lag from illness onset to diagnosis of 2 days, the curve indicates that the proportion of exposures within cabins resulting in secondary transmission was greatly reduced by the quarantine.