Coronavirus Disease Case Definitions, Diagnostic Testing Criteria, and Surveillance in 25 Countries With Highest Reported Case Counts

Amitabh B. Suthar; Sara Schubert; Julie Garon; Alexia Couture; Amy M. Brown; Sana Charania


Emerging Infectious Diseases. 2022;28(1):148-156. 

In This Article

Abstract and Introduction


We compared case definitions for suspected, probable, and confirmed coronavirus disease (COVID-19), as well as diagnostic testing criteria, used in the 25 countries with the highest reported case counts as of October 1, 2020. Of the identified countries, 56% followed World Health Organization (WHO) recommendations for using a combination of clinical and epidemiologic criteria as part of the suspected case definition. A total of 75% of identified countries followed WHO recommendations on using clinical, epidemiologic, and diagnostic criteria for probable cases; 72% followed WHO recommendations to use PCR testing to confirm COVID-19. Finally, 64% of countries used testing eligibility criteria at least as permissive as WHO. We observed marked heterogeneity in testing eligibility requirements and in how countries define a COVID-19 case. This heterogeneity affects the ability to compare case counts, transmission, and vaccine effectiveness, as well as estimates derived from case surveillance data across countries.


Novel infectious pathogens can pose major challenges to global health and security. Tracking the geography, demographics, and suspected mode of transmission of these pathogens by using a standardized case definition remains the foundation for infectious disease surveillance.[1] Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease (COVID-19), was first characterized in December 2019.[2] By January 2020, the first national case definition was developed[3] and the World Health Organization (WHO) declared a public health emergency of international concern.[4] WHO's interim guidance for global COVID-19 surveillance, released on January 31, 2020, provided a hierarchy of confirmed, probable, and suspected case definitions.[5] This guidance encouraged the use of all available clinical, epidemiologic, and laboratory evidence for case classification purposes and noted that countries might need to adapt these definitions to their unique epidemiologic situations. Recommendations for testing suspected cases and widespread testing on the basis of transmission intensity, number of cases, and available resources were included.

Both WHO and national case definitions have evolved as knowledge about COVID-19 etiology and the myriad of ways the disease manifests after infection has grown.[5–7] Early on, surveillance emphasized a travel history to Wuhan, China, where the initial outbreak occurred, and a narrowly defined set of symptoms. However, the virus rapidly spread to other provinces in China and then internationally, and reports of patients who experienced new symptoms or remained asymptomatic increased.[8] Confirming a COVID-19 case relies on diagnostic testing; therefore, testing capacity has played a vital role in COVID-19 surveillance efforts. The types of tests available have expanded to include molecular and antigen tests to detect the presence of the SARS-CoV-2 virus and serologic tests to detect antibodies produced from previous SARS-CoV-2 infection.[9,10] However, the availability of these tests and the resources needed to collect, handle, and process clinical specimens have varied widely across nations.[11] Shortages of test kits and reagents and lack of laboratory capacity have forced officials in many locations to make difficult decisions about testing eligibility.[12]

Differences in testing eligibility criteria and case definitions pose a challenge not only to detecting the actual number of cases within countries, but also to understanding the global burden of disease and adequately responding to pandemics. Global guidelines have been developed for testing eligibility criteria and case definitions but are usually reviewed at a national level and are subject to adaptation on the basis of laboratory and health system considerations. Earlier evaluations of global COVID-19 case definitions do not reflect the latest changes to national case definitions and testing eligibility criteria and do not target the full range of countries with the highest number of reported COVID-19 cases.[13–15] We analyzed national COVID-19 case definitions from the 25 countries with the largest number of reported COVID-19 cases as of October 1, 2020 (collectively representing ≈85% of the global cases at that time), and the specific criteria used to determine eligibility for diagnostic testing. We also determined the implications of intercountry differences on ongoing efforts to understand global disease burden and control the pandemic.