Development and Validation of Simple Risk Scores to Predict Hospitalization in Outpatients with COVID-19 Including the Omicron Variant

Mark H. Ebell; Roya Hamadani; Autumn Kieber-Emmons

doi:10.3122/jabfm.2022.AP.220056

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Figure 1.
Receiver operating characteristic curves.

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Table 1.

Characteristics of Included Patients in the Derivation and Internal Validation Cohort

Clinical Parameter	Not Hospitalized	Hospitalized	P Value
Vital signs
Mean age	41.9	60.2	< 0.001
Age category
< 50 years	5960	91 (1.5%)	< 0.001
50 to 59 years	1631	84 (4.9%)
60 to 69 years	1032	100 (8.8%)
70 + years	623	128 (17.0%)
Respiratory rate > 30/min	3/9246 (0.03%)	3/403 (0.74%)	< 0.001
Respiratory rate > 20/min	261/9246 (2.8%)	43/403 (10.7%)	< 0.001
Oxygen saturation ≤ 95%	330/9246 (3.6%)	111/403 (27.5%)	< 0.001
Temperature ≥ 100.4 F	433/9246 (4.7%)	36/403 (8.9%)	0.008
Comorbidities
Type 1 or 2 diabetes mellitus	806/9246 (8.7%)	142/403 (35.2%)	< 0.001
Asthma	918/9246 (9.9%)	51/403 (12.7%)	0.07
COPD or chronic bronchitis	192/9246 (2.1%)	68/403 (16.9%)	< 0.001
Hypertension	1950/9246 (21.1%)	257/403 (63.8%)	< 0.001
Cardiovascular disease	356/9246 (3.9%)	88/403 (21.8%)	< 0.001
Chronic kidney disease	151/9246 (1.6%)	55/403 (13.7%)	< 0.001
Chronic liver disease	362/9246 (3.9%)	40/403 (9.9%)	< 0.001
Cancer	340/9246 (3.7%)	49/403 (12.2%)	< 0.001
Any of the above comorbidities	3028/9246 (32.8%)	308/403 (76.4%)	< 0.001
Symptom
Dyspnea	828/9246 (9.0%)	168/403 (41.7%)	< 0.001

Notes: For age, percentage shown is percentage within an age category who were hospitalized. For all other parameters, it is the percentage of hospitalized and non-hospitalized with that comorbidity or parameter.
Abbreviation: COPD, Chronic obstructive pulmonary disease.

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Table 2.

Multivariate Models, Showing Assignment of Points Based on the Beta-Coefficients

Variable	β-Coefficient	P > z	β/Lowest β	Points
Model A: Base score, AUROCC = 0.847
Dyspnea	1.3740	0.000	1.50	1.5
Any comorbidity *	1.1146	0.000	1.22	1
Age 50 to 59 years	0.9165	0.000	1.00	1
Age 60 to 69 years	1.4885	0.000	1.62	1.5
Age 70 + years	2.1250	0.000	2.32	2.5
Constant	−5.0277
Model B: Adds fever, AUROCC = 0.850
Dyspnea	1.3807	0.0000	1.77	2
Any comorbidity *	1.1059	0.0000	1.42	1.5
Age 50 to 59 years	0.9013	0.0000	1.16	1
Age 60 to 69 years	1.4902	0.0000	1.91	2
Age 70 + years	2.1290	0.0000	2.73	3
Temperature ≥ 100.4	0.7798	0.0020	1.00	1
Constant	−5.0753
Model C: Adds respiratory rate > 20/min, AUROCC = 0.853
Respiratory rate > 20/min	0.8615	0.000	1.11	1
Dyspnea	1.3167	0.000	1.69	1.5
Any comorbidity *	1.0753	0.000	1.38	1.5
Age 50 to 59 years	0.8967	0.000	1.15	1
Age 60 to 69 years	1.4709	0.000	1.89	2
Age 70 + years	2.1074	0.000	2.71	3
Temperature ≥ 100.4	0.7784	0.002	1.00	1
Constant	−5.0856
Model D: Adds oxygen saturation ≤ 95%, AUROCC = 0.872
Oxygen saturation ≤ 95%	1.4937	0.000	2.37	2.5
Dyspnea	1.2769	0.000	2.03	2
Any comorbidity *	1.0810	0.000	1.72	1.5
Age 50 to 59 years	0.7538	0.001	1.20	1
Age 60 to 69 years	1.1124	0.000	1.77	2
Age 70 + years	1.6574	0.000	2.63	2.5
Temperature ≥ 100.4	0.6295	0.018	1.00	1
Constant	−5.1852

↵Notes: *Type 1 or 2 diabetes mellitus, asthma, COPD or chronic bronchitis, hypertension, cardiovascular disease, chronic kidney disease, chronic liver disease, or cancer.
Abbreviation: AUROCC, The area under the ROC curve.

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Table 3.

Classification Accuracy of 3 Novel Risk Scores and 2 Externally Derived Risk Scores in the Early Derivation, Late Validation, and Omicron Cohorts

	Early Derivation Cohort	Late Validation Cohort	Omicron Cohort
	Data Collection: 20 March 2020–28 February 2021	Data Collection: 1 March 2021–30 September 2021	Data Collection: 20 December 2021–7 January 2022
Risk Score (Points)	n Hospitalized/Total (%)	n Hospitalized/Total (%)	n Hospitalized/Total (%)
Overall	233/5839 (4.0%)	157/3775 (4.2%)	74/6138 (1.2%)*
Model A risk score
Low (0)	9/2660 (0.34%)	15/1849 (0.81%)	7/3144 (0.22%)
Moderate (1.0 – 2.5)	105/2600 (4.0%)	84/1623 (5.2%)	34/2613 (1.3%)
High (≥ 3.0)	120/583 (20.6%)	70/334 (21.0%)	33/381 (8.7%)
Model B risk score
Low (0 – 1.0)	15/3188 (0.47%)	19/2135 (0.89%)	7/1724 (0.41%)
Moderate (1.5 – 3.5)	96/2035 (4.7%)	80/1320 (6.1%)	22/1302 (1.7%)
High (≥ 4.0)	123/620 (19.8%)	70/351 (19.9%)	35/327 (10.7%)
Model C risk score
Low (0 – 1.0)	14/3172 (0.44%)	18/2119 (0.85%)	7/1823 (0.38%)
Moderate (1.5-3.5)	98/2043 (4.8%)	82/1328 (6.2%)	20/1478 (1.4%)
High (≥ 4.0)	131/637 (20.6%)	69/359 (19.2%)	42/445 (9.4%)
Model D risk score
Low (0 – 1.0)	10/3205 (0.33%)	16/2020 (0.79%)	5/2106 (0.24%)
Moderate (1.5- 4.5)	106/2349 (4.5%)	79/1481 (5.3%)	28/2026 (1.4%)
High (≥ 5.0)	117/465 (25.2%)	74/305 (24.3%)	50/356 (14.0%)
COVID-NoLab risk score
Low (0 to 1)	142/3544 (4.0%)	70/2488 (2.8%)	12/2081 (0.6%)
Moderate (2 to 5)	259/2254 (11.5%)	132/1302 (10.1%)	45/1253 (3.6%)
High (≥ 6)	29/45 (64.4%)	9/16 (56.3%)	7/19 (36.8%)
OutCoV risk score
Low (< 3)	163/4340 (3.8%)	81/2929 (2.8%)	18/2534 (0.71%)
Moderate (3.0 – 5.0)	220/1392 (15.8%)	112/818 (13.7%)	32/769 (4.2%)
High (≥ 5.5)	47/111 (42.3%)	18/59 (30.5%)	14/50 (28.0%)