In the fifth version of the guidelines released on February 5,
China modified its classification of confirmed cases to include diagnosis by symptoms only rather requiring confirmation by both clinical symptoms and laboratory tests.

The inclusion of these cases led to a sudden jump in confirmed cases before the authorities reversed the decision more than a week later on February 17.

The HKU team found that if the fifth definition were used throughout the epidemic, the total number of confirmed cases could have reached 232,000 by February 20, instead of the 55,508 confirmed cases throughout the country. The official tally in the HKU paper is slightly higher than the National Health Commission’s 54,965 due to reporting technicalities.