Characteristics of patients with Coronavirus Disease 2019 (COVID-19) and seasonal influenza at time of hospital admission: a single center comparative study

Abstract

Background: In the future, co-circulation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza viruses A/B is likely. From a clinical point of view, differentiation of the two disease entities is crucial for patient management. We therefore aim to detect clinical differences between Coronavirus Disease 2019 (COVID-19) and seasonal influenza patients at time of hospital admission.

Methods: In this single-center observational study, we included all consecutive patients hospitalized for COVID-19 or influenza between November 2019 and May 2020. Data were extracted from a nationwide surveillance program and from electronic health records. COVID-19 and influenza patients were compared in terms of baseline characteristics, clinical presentation and outcome. We used recursive partitioning to generate a classification tree to discriminate COVID-19 from influenza patients.

Results: We included 96 COVID-19 and 96 influenza patients. Median age was 68 vs. 70 years (p = 0.90), 72% vs. 56% (p = 0.024) were males, and median Charlson Comorbidity Index (CCI) was 1 vs. 2 (p = 0.027) in COVID-19 and influenza patients, respectively. Time from symptom onset to hospital admission was longer for COVID-19 (median 7 days, IQR 3-10) than for influenza patients (median 3 days, IQR 2-5, p < 0.001). Other variables favoring a diagnosis of COVID-19 in the classification tree were higher systolic blood pressure, lack of productive sputum, and lack of headache. The tree classified 86/192 patients (45%) into two subsets with ≥80% of patients having influenza or COVID-19, respectively. In-hospital mortality was higher for COVID-19 patients (16% vs. 5%, p = 0.018).

Conclusion: Discriminating COVID-19 from influenza patients based on clinical presentation is challenging. Time from symptom onset to hospital admission is considerably longer in COVID-19 than in influenza patients and showed the strongest discriminatory power in our classification tree. Although they had fewer comorbidities, in-hospital mortality was higher for COVID-19 patients.

Keywords: COVID-19; Classification tree; Comparative; Differences; Influenza; SARS-CoV-2.

Fig. 1

Inclusion criteria. Abbreviations: SARS-CoV-2, Severe acute respiratory syndrome corona virus 2; h, hour

Fig. 2

Hospital admission timeline

Fig. 3

Laboratory results (selected values) by patient group. Note: in the AST graphic (b.) one value (AST 538 U/l) is not displayed in the influenza group. Abbreviations: LDH, lactate dehydrogenase; AST, aspartate aminotransferase; CRP, C-reactive protein; Left shift, left shift of neutrophils; WBC, white blood cell count

Fig. 4

Recursive partitioning tree classifying patients into subsets based on symptoms and vital signs. Proportion of COVID-19 or influenza cases ≥80% in Node 4 and Node 8. Abbreviations: Latency, time from first onset of symptoms to admission to the hospital; BDsystolic, systolic blood pressure in mmHg