Lymphocyte monocyte ratio is an effective and simple predictor for nosocomial influenza outbreaks

Abstract ObjectivesNosocomial influenza outbreak detection remains challenging. We evaluated the diagnostic utility of blood cell parameters, along with their capacity to differentiate between hospital acquired influenza and coronavirus disease 2019 (COVID-19).MethodsWe retrospectively analyzed patients diagnosed with nosocomial influenza from January 2017 to December 2019, and patients with COVID-19 in early 2020 at a tertiary teaching hospital in Beijing, China. We compared the differences between blood cell count and ratios (lymphocyte-to-monocyte ratio [LMR], neutrophil-to-lymphocyte ratio [NLR], lymphocyte-to-platelet ratio [LPR]) at symptom onset, before (admission), and after (recovery) nosocomial influenza. We also compared the abovementioned parameters between influenza and COVID-19 patients.ResultsLymphocyte count, LMR, and LPR were significantly lower in the symptom onset than in the admission and recovery groups (p < 0.001), while NLR was higher (p < 0.001). LMR and NLR exhibited similar and consistent tendencies among different subgroups of patients with nosocomial influenza (p < 0.001). The area under the receiver operating curve (AUC) of LMR, NLR, LPR, and lymphocyte count were 0.914, 0.872, 0.806, and 0.866, respectively. The optimal LMR cut-off value was 2.50, with specificity and sensitivity of 92.0% and 81.3%, respectively. Peripheral blood cell ratios can help diagnose nosocomial influenza significantly earlier than conventional methods. For differentiating influenza and COVID-19, the AUCs of LMR was 0.825.ConclusionsLMR effectively predicts nosocomial influenza outbreaks, particularly during the COVID-19 pandemic when simultaneous transmission can be a substantial threat.