As of April 7, 2020, a total of 1,481 COVID-19 cases were detected in Singapore. The median age was 37 years (interquartile range [IQR] 27-53 years). The majority of cases (922/1,481, 62.3%) was admitted to NCID.
Of these cases, 923 (62.3%) were Singapore residents, 503 (34.0%) were non-residents and 55 (3.7%) were visitors. Among residents, the incidence was 22.9 cases per 100,000 population. The 20-29 age group had the highest incidence of COVID-19 while the number of detected cases was low among those below 20 years of age (Table 1).
Timely isolation of cases, being a key public health intervention for disease control, was evaluated. The median time of isolation of cases from disease onset was 4 days (IQR 2-7 days) and was longer in older age groups (HR = 0.72 for cases aged ≥ 70, 95% CI 0.55-0.95, p=0.005) (Table 2). However, after adjustment for linkage to a known cluster, age was no longer associated with a difference in the rate at which cases were isolated (aHR = 0.83 for cases aged ≥ 70, 95%CI 0.63-1.09 p=0.19; overall effect of age p=0.16).
The median duration from hospital admission to discharge was 15 days (IQR 11-19 days). The duration of hospitalisation was significantly longer in the older age groups (≥70years compared with < 30 years, HR 0.20, 95%CI 0.07-0.58). The corresponding duration from disease onset to hospital discharge was 20 days (IQR 16-25 days) and was also longer in the older age groups (≥70years compared with < 30 years, HR 0.27, 95%CI 0.09-0.80) (Table 2). As of 7 April 2020, two COVID-19 deaths were recorded.
Age, Oxygen Supplementation and Mechanical Ventilation
Overall, an estimated 11.4% of all cases required oxygen supplementation, with half of them requiring it by day 8 of illness (IQR 6-11 days). Less than 1% of cases below 30 years old required oxygen. This proportion increased to 20% for persons aged 50-59 years and 40.9% for persons aged 70 and above (p<0.001) (Table 2).
This age-specific increased risk was similarly seen for mechanical ventilation needs. Overall, an estimated 4.8% of cases required mechanical ventilation. The median duration from disease onset to mechanical ventilation was 8 days (IQR 5-10 days). None below 30 years required mechanical ventilation, but the proportion increased after age 50 years, with an estimated 19.3% (95% confidence interval [95% CI] 13.2%-27.8%) of cases aged 60 to 69 years requiring it (Table 2).
The median duration of oxygen supplementation was 11 days (IQR 5 – 25 days) and median duration of mechanical ventilation was 14 days (IQR 8-21 days). Older persons required a longer duration of increased care, with statistically significant differences in the rates of oxygen supplementation (p<0.01) and mechanical ventilation (p=0.041) between age groups (Table 2).
Chest Radiography, Oxygen Supplementation and Mechanical Ventilation
In a subgroup analysis of patients at NCID, the finding of pneumonia on CXR at admission was an independent predictor of oxygen supplementation and mechanical ventilation (Table 3). The timing of this investigation in the course of illness corresponded to the time to isolation, which was a median of four days. Patients with pneumonia on CXR had higher risk of requiring oxygen supplementation (aHR 4.15, 95%CI 2.29-7.53, p<0.001) and mechanical ventilation (aHR 3.84, 95%CI 1.36-10.85, p=0.011).
Performance of Age and Abnormal CXR in Predicting Clinical Outcomes
Age discriminated cases who subsequently required oxygen supplementation (area under ROC curve [AUROC] 0.736, 95%CI: 0.667-0.805; Figure 1A) or mechanical ventilation (AUROC 0.772, 95%CI 0.699-0.845; Figure 1B). A cut-off of 55 years and above achieved sensitivity of 57% and specificity of 72% for the outcome of oxygen supplementation, and sensitivity of 64% and specificity of 70% for the outcome of mechanical ventilation.
In the subgroup of patient admitted to NCID for whom CXR data was available, an abnormal CXR had sensitivity of 55% and specificity of 75% for supplemental oxygen, and sensitivity of 60% and specificity of 71% for mechanical ventilation (Table 4).
When the cut-off age ≥ 55 years and abnormal CXR were combined to identify cases who met either criteria, sensitivity of 83% and specificity of 63% were observed for supplemental oxygen while sensitivity of 87% and specificity of 58% were attained for mechanical ventilation (Table 4).