5 Case Diagnosis

Case definitions were classified into “observed cases” and “confirmed cases” in the first edition.

The definition of observed cases is one should meet both the epidemiological exposure history(having a travel history in Wuhan, or relevant local markets, especially having direct or indirect contact history with farmers’ markets two weeks before disease onset)and the clinical definition of unexplained viral pneumonia in 2007(fever, radiographic features of pneumonia, the white blood cell count is normal or decreased in the early stage, or the lymphocyte count is decreased,or the condition is not significantly improved or progressively aggravated after 3 days of standard antibiotic treatment). For confirmed cases, the respiratory tract specimens,such as sputum and oral swab, should be collected fromobserved case for whole genome sequencing and it should be highly homologous with the new coronavirus.

Since increasing cases were not exposed to Wuhan Huanan seafood market and the epidemiological exposure history emphasized “having a history of travel in Wuhan within 14 days before the disease onset”, the second edition changed the “observed cases” to “suspected cases”, and “having a history of travel in Wuhan within 14 days before the disease onset” plus clinical manifestations of viral pneumonia could be considered as suspected cases.That “the 3-day antibacterial treatment is invalid” was deleted. The sensitivity of early detection of cases was enhanced. What’s more, confirmed cases were detected by real-time fluorescence RT-PCR.

Case definitions are different between Hubei Province and other provinces except Hubei in the fifth edition. Cases are still classified into“suspected cases” and “confirmed cases” in provinces except Hubei. But“clinically diagnosed cases” defined as suspected cases with imaging features of COVID-19 has been added in the case classification in Hubei Province.Moreover, the criteria for suspected cases are further broadened to people with “fever and/or respiratory symptoms” and “normal or decreased white blood cell count, or decreased lymphocyte count in the early stage”.

Different case definitions for Hubei Province and other provinces except Hubei are deleted in the sixth edition and unified as “suspected cases” and“confirmed cases”.

Suspected case definitions are based on two different scenarios:(1)“Meeting with any one of the epidemiological exposure histories and in accordance with any two of clinical manifestations(fever and/or respiratory symptoms; have the above-mentioned imaging features of pneumonia; the total leukocyte count was normal or decreased, or the lymphocyte count decreased in the early stage of the disease).” and(2)“Meeting with all three of clinical manifestations(fever and/or respiratory symptoms; having the above-mentioned imaging features of pneumonia; the total leukocyte count was normal or decreased, or the lymphocyte count decreased in the early stage of the disease)but without specific epidemiological exposure history.”.

“Severe cases” has been added to the case classification since the second edition, and the definition of critical cases remains unchanged. “Ordinary type” was added in the fourth edition and severe case definition was slightly modified(“pulmonary imaging shows multiple lobar lesions, or >50% lesions progression within 48 hours and other clinical conditions requiring hospitalization”was deleted). In the fifth edition, the definition of “mild type” is added,namely, the mild clinical symptoms, and no sign of pneumonia observed by imaging diagnosis.