Study population and local epidemic curves
Between November 25th 2019 and May 7th 2020, 112 patients were hospitalized with COVID-19, and 118 with seasonal influenza. Thereof, 96 COVID-19 and 96 influenza patients were included in the study (Figure 1). Whereas patients with influenza were hospitalized between November 25th and March 26th (with a peak in February 2020), the first COVID-19 patient was admitted on March 10th; a peak of hospitalized COVID-19 was reached by the end of March 2020 (Figure 2).
Patients had a median age of 68 years (IQR 57-81) for COVID-19 and 70 (IQR 57-80) years for influenza (p=0.90); males were more common among COVID-19 patients (72% vs 56%, p=0.024); COVID-19 patients were more often transferred from long-term care or rehabilitation clinics than influenza patients (15% vs 5%, p=0.030). The proportion of active smokers was lower in COVID-19 compared to influenza patients (4% vs 13%, p=0.033). COVID-19 patients had less comorbidities compared to influenza patients (median CCI 1 vs 2, p=0.027), which was mostly due to less chronic renal disease (21% vs 35%, p=0.025), less oncological disease (8% vs 26% p=0.001), and less chronic respiratory disease (10% vs 21%, p=0.047) (Table 1).
Time from onset of symptoms to hospital admission was longer in the COVID-19 group (median 7 days, IQR 3-10) compared to the influenza group (median 3 days, IQR 2-5, p<0.001). The most commonly reported symptoms were cough (69% vs 76%, p=0.258) and fever (68% vs 65%, p=0.647) in both groups. Symptoms were similar between groups except that COVID-19 patients more frequently reported dyspnea compared to influenza patients (49% vs 32%, p=0.019). On the other hand, coryza (7% vs 13%, p=0.029) and sore throat (2% vs 18%, p=0.006) were less common among COVID-19 compared to influenza patients (Table 2).
Vital signs and clinical scores
COVID-19 patients had a higher systolic blood pressure of 137 mmHg (IQR 120-150 mmHg) compared to influenza patients (median 129 mmHg, IQR 116-138mmHg, p=0.008). The median oxygen saturation (on room air) was slightly lower in the COVID-19 group (93%, IQR 91-95% versus 94%, IQR 92-97%, p=0.033). CURB-65 and quick-SOFA scores were similar between groups (Table 3).
COVID-19 patients had a higher median lactate dehydrogenase of 381 U/l (IQR 276-513 U/l) in comparison to 286 U/l (IQR 233-372 U/l, p=0.001) in influenza patients. Furthermore, gamma-glutaminetransferase (median 44 U/l, IQR 28-69 U/l vs 31 U/l, IQR 22-52 U/l, p=0.004) and aspartate transaminase (median 47 U/l, IQR 32.5-70 U/l vs 33 U/l, IQR 22-43 U/l, p=0.001) were higher in COVID-19 compared to influenza patients. Median C-reactive protein (CRP) was similar in both groups (72 mg/l, IQR 28-146 vs 50 mg/l, IQR 19-118). The median white blood cell count was lower in COVID-19 (5.9 G/l, IQR 4.3-8.3G/l) in comparison to influenza patients (7.5 G/l, IQR 4.8-9.9 G/l, p=0.040), and band neutrophils were also less common, with 10% (IQR 5-14%) in the COVID-19 group versus 18% (IQR 9-27%, p=0.006) in the influenza group (Figure 3).
Other microbiology results
Blood cultures were positive with relevant pathogens in 2/77 (2%) COVID-19 and in 8/73 (8%) influenza patients (p=0.100). Zero out of 10 (0%) COVID-19 patients and two out of nine (2%) influenza patients had a positive streptococcal urine antigen (p=0.368).
The following variables were predictive for COVID-19 in the recursive partitioning tree (Figure 4): longer time from symptom onset to hospital admission (>5 days), systolic blood pressure >141 mmHg, lack of productive sputum, and lack of headache. No laboratory values were identified as relevant predictors in this analysis. Two out of five classification subsets including 86 of 192 patients (45%) were considered as clinically helpful: node 4 (a combination of symptom onset ≤ 5days, systolic blood pressure ≤141mmHg, and presence of headache) with 96% of influenza patients and node 8 (combination of symptom onset >5 days and lack of productive sputum) with 80% of COVID-19 patients (Figure 4). The three other subsets, including 106 patients (55%), included similar proportions of the two diseases and therefore provided no useful information. In other words, if the associated variable combinations had been used for diagnosis, 73 patients (38%) would have been diagnosed correctly, 13 patients (7%) would have been diagnosed incorrectly, and no diagnosis would have been made for 106 patients (55%).
The proportion of ICU admissions was similar between COVID-19 and influenza patients (19% vs 16%, p=0.566). The median ICU LOS was 4 days (IQR 1.5-15) for COVID-19 and 2 days (IQR 1-8, p=0.138) for influenza patients. However, median hospital LOS was 8 days (IQR 4-12 days) for COVID-19 and 5 days (IQR 3-9 days) for influenza patients (p=0.014). Antibiotic treatment was less (22% vs 46%, p<0.001) and corticosteroids were more frequently (10% vs 1%, p=0.005) administered to COVID-19 patients than to influenza patients. In-hospital mortality was considerably higher in COVID-19 patients in comparison to influenza patients (16% vs 5%, p=0.018).