正當中國每天新確診的新冠肺炎（COVID-2019）人數看似趨穩之際，2月12日確診數字突然大幅躍升，從2015人升至15152人，增幅超過750%。新增病例中絕大多數來自湖北，該省當天新確診人數從1638人增至14840人，其中省會武漢的新確診人數從1104人增至13436人。這一出人意料的猛增，令包括CNN和《紐約時報》在內的多家西方媒體再次指責中國政府缺乏透明度。

這種大幅上升可以用中國國家衛健委公布的數據來解釋。它是由於湖北改變了“確診”定義，為的是與內地其他地區的定義統一，使全國數據具有可比性。而內地其他地區的確診標準並無改變。

2月12日之前，湖北確定新冠肺炎的標準一直比內地其他地區更嚴格。在確診的三、四個標準當中，包括要求患者進行的特定冠狀病毒血液檢測呈陽性。即使患者符合其他所有標準，並且觀察到了臨床癥狀，但測試不呈陽性的話，也不會被歸入確診病例。而根據新定義，只要滿足其他條件，這個條件不再是絕對必要的。定義的這種改變，導致之前一些未確診的病例被歸入了確診病例，其結果就是湖北的確診人數一次性急劇增加。然而，基本情況是不變的。雖然隨着更多舊的病例被重新歸類，每日新確診人數有可能持續幾天大量增加，但最終會降到定義改變之前的水平。

我利用中國政府公布的各地數據，試着估計自2月12日以來按舊定義確診的病例數量。結果顯示（圖1），按照舊定義（實線），湖北省內省外新確診人數仍保持着普遍下降的趨勢。圖1中的虛線是湖北及其武漢、黃岡兩個城市按新定義確診的病例數，在2月12日出現大幅上升後，2月13日大幅下降，2月14日則恢復到改變定義之前的水平。數據急升完全是由於湖北改變了確診的定義，整個內地新確診的15034例中，湖北增加14840例，湖北以外的人數則未受影響。

圖2顯示的是按照新定義，湖北和內地其他地區每天的新確診人數。很顯然，湖北的新確診人數在2月12日大幅躍升後，到2月14日已經如預期那樣基本恢復正常。2月14日新確診2420人，低於2月9日定義改變之前的2618人。確診人數下行的趨勢將恢復。自從2月3日開始，內地除湖北省以外，其他的病例已經在持續下降，這是最令人鼓舞的，它意味着冠狀病毒在內地其他地區已經得到控制，只要湖北繼續被封鎖，這一狀況就會保持下去。

改變對單個病患的確診定義，使之與內地其他地區所採用的定義相一致，這是完全合理的。也許早就應該這麼做，但遲做總比不做好。就在過去幾天，湖北經歷了政治領導層的更換，新領導是絕對沒有理由瞞報新確診病例數量的。

Just when the daily number of newly confirmed COVID-2019 coronavirus cases seemed to have levelled off in China, it has an unexpected steep jump, from 2,015 to 15,152 on 12 February, or more than 750%. The overwhelming bulk of the increase came from the Province of Hubei, where the number of newly confirmed cases increased from 1,638 to 14,840 on 12 February. Similarly, the number of newly confirmed cases in Wuhan, the capital of Hubei, increased from 1,104 to 13,436 on 12 February. This unexpected steep jump has brought back accusations of lack of transparency on the part of the Chinese government in a number of Western media including the CNN and the New York Times.

This jump can be explained on the basis of data published by the National Health Commission of China. It was the result of a change in the definition of a “confirmed case” adopted by Hubei so that it conforms to the definition used in the rest of the Mainland, making the data comparable nationally. There was no change in the criteria for a confirmed case in the rest of the Mainland.

Before 12 February, Hubei had maintained a stricter criteria for a confirmed coronavirus case than the rest of the Mainland. Among the three or four criteria for the determination of a confirmed case, it was necessary for a patient to be tested positive by a specific blood test for the coronavirus virus. Even if a patient satisfied all of the other criteria, and despite observed clinical symptoms, he or she would not be classified as a confirmed case without this positive test. Under the new definition, this condition is no longer absolutely necessary, as long as the other criteria are satisfied. This change in the definition led to the reclassification of some previously unconfirmed cases as confirmed cases, resulting in a steep one-time increase in the number of confirmed cases in Hubei. However, the underlying situation remained the same. While the high daily numbers may continue for a couple more days as additional old cases are reclassified, they should eventually settle down to the pre-definitional-change levels.

I have made an attempt to estimate the numbers of the newly confirmed cases under the old definition since 12 February, using the geographically disaggregated data published by the Chinese government. The results are presented in Chart 1, which shows that under the old definition (the solid lines), the numbers of newly confirmed cases have continued their generally downward trends both inside and outside of Hubei. The numbers of the newly confirmed cases under the new definition for Hubei and its two cities, Wuhan and Huanggang, are also presented in Chart 1 as broken lines. It shows a steep jump on 12 February, and then a steep fall on 13 February, and a return to a level comparable to the pre-definitional change period on 14 February. The jump was caused exclusively by the change of definition for Hubei, which accounted for an increase of 14,840 out of a total of 15,034 newly confirmed cases for the Mainland as a whole. The numbers of cases outside of Hubei were unaffected.

In Chart 2 we present the daily number of newly confirmed cases in Mainland ex Hubei and in Hubei under the new definition. It is clear that the number of newly confirmed cases in Hubei has returned more or less to normal on 14 February after the steep jump on 12 February, as expected. It was 2,420 on 14 February, lower than 2,618, the number on 9 February, before the change in the definition. It looks ready to resume its downward trend. The number of cases for Mainland ex Hubei has continued to decline since it began doing so on 3 February. This is most encouraging--it means that the coronavirus is under control elsewhere on the Mainland and should remain so as long as Hubei continues to be sealed off.

The change in the definition of a confirmed case to conform to the definition used in the rest of the Mainland is completely justified. It probably should have been done some time ago, but better late than never. Hubei just underwent a change in political leadership within the past couple of days. There is absolutely no incentive for the new leaders to understate the number of newly confirmed cases.