Evaluation of COVID-19 and Influenza-like Illness Surveillance Case Definitions in a Prospective Cohort of Healthcare Personnel in Peru

Background Public health agencies employ case definitions for influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections to optimize surveillance, monitor disease trends, and inform decision-making, particularly in limited resource settings. Methods Using a prospective healthcare personnel cohort in two hospitals in Lima, Peru (July 2022–June 2023), we compared and evaluated the performance of three symptom profiles of three common surveillance case definitions to identify influenza and SARS-CoV-2 infections: influenza-like illness, coronavirus disease 2019–like illness (CLI), and acute respiratory infection. Participants with an acute respiratory illness reported symptom progression twice weekly. Participants self-collected nasal swabs for SARS-CoV-2 and influenza reverse transcription real-time polymerase chain reaction testing. Sensitivity, specificity, and positive and negative predictive values of each case definition were evaluated. Results Of 1623 participants enrolled, 1450 illness episodes were reported; 92 (6%) were positive for influenza, 350 (24%) for SARS-CoV-2, and 3 (0.2%) were positive for both. For the four influenza-like illness case definitions evaluated, all yielded low sensitivity for detection of influenza (points estimate range, 23%–35%) and SARS-COV-2 (range, 21%–29%), but high specificity (83%–90% and 86%–92%, respectively). In contrast, the acute respiratory infection and coronavirus disease 2019–like illness definitions both yielded high sensitivity (83%–100%) and low specificity (2%–41%) for detection of both influenza and SARS-CoV-2. Conclusions The performance of case definitions was similar for influenza and SARS-CoV-2 supporting the use of the same definitions by surveillance networks. The substantial differences in sensitivity and specificity across the case definitions necessitate surveillance objectives and cost considerations in selecting a case definition fit for purpose.