Effectiveness of COVID-19 case definition in identifying SARS-CoV-2 infection in northern Mexico

Abstract

INTRODUCTION In Mexico, a new COVID-19 case definition was released on 24 March 2020, this definition is no different from the one used for epidemiological surveillance of influenza-like illness since 2009. We aim to evaluate the effectiveness of the COVID-19 suspected case definition in identifying SARS-CoV-2 infection in Tijuana, a US-border city in Mexico. METHODS A cross-sectional database study was conducted, including entries from 11 March to 1 May 2020. COVID-19 case definition was compared to RT-PCR results using 2×2 tables to estimate sensitivity, specificity, PPV, NPV, accuracy and likelihood ratios (LR). Categorical variables were analyzed using χ2 test. Stratification by gender, age group, history of chronic disease and severity of presentation was performed to control for confounding. RESULTS From a total of 10216 entries, 897 patients with results from RT-CPR for SARS-CoV-2 were included. There was no significant association between COVID-19 case definition and RT-PCR result (χ2=0.750, df=1, p=0.386). A sensitivity of 87.45%, specificity of 10.61%, PPV of 61.69%, and NPV of 33.96% were calculated, with an overall accuracy of 58.42%, LR+ was 0.98 and LR- was 1.18. Stratifying by age, homogeneity of OR=0.024 showed an association between case definition and test result particularly among those aged 16–39 years (p=0.014). Only 4 individual symptoms had a statistical association with RT-PCR result. These were dyspnea (p<0.001), odynophagia (p<0.001), rhinorrhea (p<0.001) and fever (p=0.008). CONCLUSIONS Satisfying criteria for COVID-19 case definition neither showed a significant association nor is it a powerful predictor for SARS-CoV-2 infection among the study population. However, this COVID-19 case definition better identifies those cases in those aged 16–39 years, suggesting a possible relation between the type of the clinical presentation and age.