Importance of adequate COVID-19 case definitions in the SARS-CoV-2 pandemic

Background: Epidemiologic case definitions serve a myriad of purposes during a pandemic, including contact tracing and monitoring disease trends. It is unknown how any COVID-19 case definition fares against the current gold standard of molecular or antigen tests. Methods: We calculated the diagnostic properties of five COVID-19 definitions (three of the Mexican government and two of the WHO) using open data of suspected COVID-19 cases in Mexico City from March 24th 2020 until January 31st 2021. Results: All 1,632,420 people included in the analysis met the WHO suspected case definition (sensitivity 100%, specificity 0%). The WHO probable case definition was met by 1.4%, while the first and second Mexican suspected case had sensitivities of 61 and 62% and specificities of 58 and 62%, respectively. Confirmed case by epidemiological contact had a low sensitivity (33%) but slightly higher specificity (77%). Conclusions: Case definitions should maximize sensitivity, especially in a high-transmission area such as Mexico City. The WHO suspected case definition has the potential for detecting most symptomatic cases. We underline the need for routine evaluation of case definitions as new evidence arises to maximize their usefulness.