Diagnostic precision of local and World Health Organization definitions of symptomatic COVID-19 cases: an analysis of Mexico's capital

OBJECTIVES: Case definitions are vital in a pandemic to effectively identify, isolate, and contact trace, particularly where testing is slow, scant, or not available. While case definitions have been developed in the COVID-19 pandemic, their diagnostic properties have not been adequately assessed. This study's objective is to determine the diagnostic properties of local and World Health Organization (WHO) COVID-19 case definitions in the large metropolitan area of Mexico City. 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 May 15th, 2021. RESULTS: All 2,564,782 people included in the analysis met the WHO suspected case definition (sensitivity: 100%, specificity: 0%). The WHO probable case definition was met by 1.2%, while the first and second Mexican suspected case had sensitivities of 61% and specificities of 61% and 67%, respectively. Confirmed case by epidemiological contact had a low sensitivity (32%) but slightly higher specificity (81%). 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.