正当中国每天新确诊的新冠肺炎（COVID-2019）人数看似趋稳之际，2月12日确诊数字突然大幅跃升，从2015人升至15152人，增幅超过750%。新增病例中绝大多数来自湖北，该省当天新确诊人数从1638人增至14840人，其中省会武汉的新确诊人数从1104人增至13436人。这一出人意料的猛增，令包括CNN和《纽约时报》在内的多家西方媒体再次指责中国政府缺乏透明度。

这种大幅上升可以用中国国家卫健委公布的数据来解释。它是由于湖北改变了“确诊”定义，为的是与内地其他地区的定义统一，使全国数据具有可比性。而内地其他地区的确诊标准并无改变。

2月12日之前，湖北确定新冠肺炎的标准一直比内地其他地区更严格。在确诊的三、四个标准当中，包括要求患者进行的特定冠状病毒血液检测呈阳性。即使患者符合其他所有标准，并且观察到了临床症状，但测试不呈阳性的话，也不会被归入确诊病例。而根据新定义，只要满足其他条件，这个条件不再是绝对必要的。定义的这种改变，导致之前一些未确诊的病例被归入了确诊病例，其结果就是湖北的确诊人数一次性急剧增加。然而，基本情况是不变的。虽然随着更多旧的病例被重新归类，每日新确诊人数有可能持续几天大量增加，但最终会降到定义改变之前的水平。

我利用中国政府公布的各地数据，试着估计自2月12日以来按旧定义确诊的病例数量。结果显示（图1），按照旧定义（实线），湖北省内省外新确诊人数仍保持着普遍下降的趋势。图1中的虚线是湖北及其武汉、黄冈两个城市按新定义确诊的病例数，在2月12日出现大幅上升后，2月13日大幅下降，2月14日则恢复到改变定义之前的水平。数据急升完全是由于湖北改变了确诊的定义，整个内地新确诊的15034例中，湖北增加14840例，湖北以外的人数则未受影响。

图2显示的是按照新定义，湖北和内地其他地区每天的新确诊人数。很显然，湖北的新确诊人数在2月12日大幅跃升后，到2月14日已经如预期那样基本恢复正常。2月14日新确诊2420人，低于2月9日定义改变之前的2618人。确诊人数下行的趋势将恢复。自从2月3日开始，内地除湖北省以外，其他的病例已经在持续下降，这是最令人鼓舞的，它意味着冠状病毒在内地其他地区已经得到控制，只要湖北继续被封锁，这一状况就会保持下去。

改变对单个病患的确诊定义，使之与内地其他地区所采用的定义相一致，这是完全合理的。也许早就应该这么做，但迟做总比不做好。就在过去几天，湖北经历了政治领导层的更换，新领导是绝对没有理由瞒报新确诊病例数量的。

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.