Until January 18th: A suspected novel coronavirus-infected pneumonia (NCIP) case was defined as a case that fulfilled all of the following criteria: "fever, with or without recorded temperature; radiographic evidence of pneumonia; low or normal white-cell count or low lymphocyte count; and no reduction in symptoms after antimicrobial treatment for 3 days, following standard clinical guidelines " OR was linked to Huanan Seafood Wholesale Market or contact with other patients with similar symptoms and fulfilled the first three criteria above.

January 18th and later: Cases were determined by a travel history to Wuhan or direct contact with patients from Wuhan who had fever or respiratory symptoms, within 14 days before illness onset. A confirmed case was "a case with respiratory specimens that tested positive for the 2019-nCoV by at least one of the following three methods: isolation of 2019-nCoV or at least two positive results by real-time reverse-transcription–polymerase-chain-reaction (RT-PCR) assay for 2019-nCoV or a genetic sequence that matches 2019-nCoV."