Last week, the World Health Organization (Who ) reported a spike in the number of cases of COVID-19 in Hubei, China. The sharp rise in cases is due to a new case definition that now includes both laboratory-confirmed cases and clinically diagnosed cases. The spike in the number of cases in Hubei has raised questions about the case definition used in China for COVID-19. The WHO has requested additional information from China on the clinically diagnosed cases that are now included in the case definition of the disease. Figure 1 presents both laboratory-confirmed cases and clinically diagnosed cases of COVID-19 in Hubei, China. Based on data from the WHO situation reports, the number of daily incident cases, including both laboratory-confirmed and clinically diagnosed, has been decreasing in Hubei, China.

Should the sharp rise in COVID-19 cases be concerning? During an outbreak, a clear case definition should be developed early in order to aid an effective epidemiological investigation of the disease. However, case definitions that are developed during an early outbreak investigation can be broad due to the lack of information about the disease. A substantial amount of information is needed to establish a final case classification. It is not uncommon for case definitions to be revised and for patients to be reclassified based on the new case definition. Case definitions can also vary by degree of certainty of diagnosis, such as confirmed, probable, or suspect. In this particular outbreak, the case definition of COVID-19 has been broadened by China to include clinically diagnosed cases that are based on symptoms and exposure.

The change in the COVID-19 case definition to include clinically confirmed cases reflects the urgency to understand the magnitude of the disease and treat suspected cases early. The expanded case definition will also allow investigators to implement control and prevention measures as early as possible and gain a better understanding of the cause of the disease. However, diagnosing a case based only on symptoms can present additional challenges such as the inclusion of other illnesses that have similar symptoms to COVID-19, which may present challenges when interpreting numbers. As research on COVID-19 continues to grow, the case definition may also change and become more specific. As of now, the broad case definition can allow investigators in China to be more inclusive of all types of COVID-19 cases in order to provide early treatment and gather more data on the disease.