Survival of Hospitalized COVID-19 Patients in Northern Italy: A Population-Based Cohort Study by the ITA-COVID-19 Network

Figures & data

Table 1 Baseline Patient Characteristics, Deaths, and Case Fatality Rate per 1000 Person-Days, by Study Area, Age, Sex, and the Charlson Index

	All patients		Person-time (days)	No. deaths	CRF (per 1,000 p-d)
	No.	(%)
Total	42,926		1,016,708	11,205	11.02
Study area
Lombardy	38,715	90.2	965,129	10569	10.95
Veneto	3229	7.5	39,640	439	11.07
Reggio E.	982	2.3	11,939	197	16.50
Age, years
18-49	5561	13.0	159,252	141	0.89
50-59	7172	16.7	204,144	451	2.21
60-69	8754	20.4	233,431	1484	6.36
70-79	10,953	25.5	244,025	3867	15.85
80-89	8880	20.7	154,177	4343	28.17
≥90	1606	3.7	21,679	919	42.39
Gender
Males	26,873	62.6	635,776	7662	12.05
Females	16,053	37.4	380,932	3543	9.30
Charlson index
0	29,775	69.4	753,537	5805	7.70
1-2	10,575	24.6	220,501	4018	18.22
≥3	2576	6.0	42,670	1382	32.39

Abbreviation: No, number; CFR, Case Fatality Rate; p-d, person-days; Reggio E., Reggio Emilia.

Figure 1 Kaplan–Meier survival curves for hospitalized COVID-19 patients in Northern Italy, 21 February–21 April 2020. (A): overall; (B): stratified by age groups; (C): stratified by sex at birth; (D): stratified by the Charlson Index.

Table 2 Proportion of Surviving Patients at 30 Days from Hospitalization, Estimated Using the Kaplan–Meier Survival Function, by Study Area, Age, Sex, and the Charlson Index

	Cumulative survival rate % (95% CI)
	All patients	Age category
		18-49 years	50-59 years	60-69 years	70-79 years	80-89 years	≥90 years
Overall	72.4 (71.9–72.8)	97.2 (96.0–97.7)	93.3 (92.0–94.0)	82.0 (81.0–82.9)	63.0 (62.0–64.0)	47.5 (46.4–48.7)	35.1 (32.4–38.0)
Study area
Lombardy	71.9 (71.5–72.4)	97.1 (96.6–97.6)	93.3 (92.7–93.9)	81.5 (80.6–82.4)	62.0 (61.0–63.0)	46.6 (45.4–47.8)	34.4 (31.5–37.4)
Veneto	72.8 (69.0–76.5)	99.5 (98.5–100)	94.6 (91.5–97.7)	86.6 (77.9–96.2)	68.7 (61.4–77.0)	52.4 (45.6–60.2)	37.3 (27.3–51.1)
Reggio E.	71.1 (66.5–76.0)	-	90.3 (83.1–98.1)	83.2 (73.3–94.5)	69.1 (59.6–80.1)	59.2 (52.0–67.4)	39.4 (26.5–58.6)
Sex
Males	70.1 (69.0–70.7)	96.6 (96.0–97.3)	92.0 (91.0–92.8)	79.4 (78.0–80.5)	58.7 (57.5–59.9)	41.1 (39.6–42.6)	28.6 (24.5–33.3)
Females	76.3 (75.0–77.0)	98.1 (97.0–98.7)	96.1 (95.0–96.9)	87.7 (86.4–89.1)	71.5 (70.0–73.1)	56.0 (54.3–57.8)	39.2 (35.7–42.9)
Charlson index
0	79.3 (78.0–79.8)	97.7 (97.0–98.1)	94.5 (93.9–95.1)	85.5 (84.0–86.4)	67.2 (66.0–68.4)	51.7 (50.1–53.3)	38.7 (34.9–42.9)
1-2	59.8 (58.8–60.8)	92.0 (89.0–95.0)	87.9 (85.6–90.2)	73.8 (71.7–76.0)	59.5 (57.8–61.2)	45.6 (43.7–47.4)	34.4 (30.2–39.3)
≥3	41.9 (39.8–44.1)	75.4 (60.0–94.7)	64.3 (54.2–76.3)	55.9 (50.3–62.1)	43.7 (40.1–47.6)	36.6 (33.5–40.0)	23.4 (16.8–32.5)

Abbreviation: 95% CI, 95% confidence interval; Reggio E., Reggio Emilia.

Figure 2 Kaplan–Meier survival curves for hospitalized COVID-19 patients in Northern Italy stratified by age and the Charlson Index, 21 February–21 April 2020. (A): age 18–49 years; (B): age 50–59 years; (C): age 60–69 years; (D): age 70–79 years; (E): age 80–89 years; (F): age 90+ years.

Table 3 Risk of Death for Hospitalized COVID-19 Patients, Estimated Using Cox Proportional Hazards Models for Age, Sex, and Charlson Index. The Model is Adjusted for All Reported Variables and Study Area and Shows the Interaction Between Charlson Index and Age

	HR (95% CI) Unadjusted	HR (95% CI) Adjusted	HR (95% CI) Adjusted*
Age, years
18–49	ref	ref	ref
50–59	2.49 (2.06–3.01)	2.39 (1.98–2.89)	2.43 (1.95–3.02)
60–69	7.04 (5.92–8.37)	6.46 (5.44–7.68)	6.60 (5.40–8.06)
70–79	16.8 (14.2–19.8)	14.8 (12.5–17.5)	17.8 (14.7–21.7)
80–89	27.6 (23.3–32.6)	24.3 (20.5–28.8)	31.7 (26.1–38.5)
≥90	37.5 (31.4–44.8)	36.2 (30.3–43.3)	52.6 (42.6–65.0)
Sex
Males	ref	ref	ref
Females	0.77 (0.74–0.80)	0.66 (0.63–0.68)	0.65 (0.63–0.68)
Charlson Index
0	ref	ref	ref
1–2	2.24 (2.15–2.33)	1.32 (1.26–1.37)	3.74 (2.45–5.70)
≥3	3.65 (3.44–3.87)	1.76 (1.66–1.87)	15.2 (7.08–32.7)
Sex x Charlson Index
Age 18–49 × CCI 0			ref
Age 50–59 × CCI 1–2			0.67 (0.42–1.08)
Age 60–69 × CCI 1–2			0.53 (0.34–0.81)
Age 70–79 × CCI 1–2			0.34 (0.22–0.52)
Age 80–89 × CCI 1–2			0.31 (0.20–0.48)
Age ≥90 × CCI 1–2			0.26 (0.17–0.41)
Age 50–59 × CCI ≥3			0.46 (0.20–1.08)
Age 60–69 × CCI ≥3			0.25 (0.11–0.54)
Age 70–79 × CCI ≥3			0.13 (0.06–0.28)
Age 80–89 × CCI ≥3			0.09 (0.04–0.20)
Age ≥90 × CCI ≥3			0.07 (0.03–0.16)

Notes: *Interpretation of HR with the interaction term: in the model with the interaction terms, the HRs of CCI decline with increasing age. For instance, the HR of CCI 3+ for the age class 50–59 is equal to the HR of CCI 3+ (15.2) multiplied by the interaction term of CCI 3+ and age class 50–59 (0.46) -> 15.2 × 0.46 = 6.99. Similarly, HR for CCI 3+ and age 70–79 is equal to 15.2 × 0.13 = 1.98.

Abbreviations: HR: hazard ratio; CI: confidence interval; ref.: reference; CCI: Charlson Comorbidity Index