Between 21 February and 31 November 2020, our clinical centres admitted 1,179 COVID-19 patients: 921 Italians (78.1%) and 258 immigrants (21.9%). Figure 1 shows monthly enrolment during the study period: there was no difference in the proportion of immigrants enrolled during the first wave of the pandemic (21 February-30 April) and the second (1 October-31 November).
Table 1 shows the patients’ baseline demographic and clinical characteristics. The Italians were significantly older than the immigrants (median age 70 years, IQR 58–79 vs 51 years, IQR 41–60; p < 0.001), and more frequently had one or more co-morbidities (79.1% vs 53.9%; p < 0.001), particularly cardiovascular (60.6% vs 29.5%) and oncological diseases (14.5% vs 6.9%) (p < 0.001 for both). The median time between the onset of COVID-19 symptoms and hospital admission was shorter among the immigrants (6 days, IQR 3–9 vs 7 days, IQR 3–19; p = 0.026), but there was no between-group difference in disease severity upon hospital admission.
Ninety-nine of the immigrants (38.4%) came from Latin America (mainly from Peru, Ecuador, and El Salvador); 72 (27.9%) from Asia (mainly from The Philippines, Bangladesh, and China); 50 (19.4%) from Africa (mainly from Egypt and Morocco); and 37 (14.3%) from central/eastern Europe (mainly Ukraine, Albania, and Romania). Table 2 shows the differences in the demographic and clinical characteristics of the immigrants by region of origin. The patients from central/eastern Europe included more women (51%) than the other groups (p = 0.015). The patients from Latin America were characterised by a non-statistically significant higher prevalence of obesity and a longer time interval between symptom onset and hospital admission than the other non-Italians (p = 0.015), and less frequent diagnoses of mild disease upon admission (p = 0.011).
Two hundred and seventy-eight of the 1,179 patients (23.5%) died in hospital within a median of 12 days after admission (IQR 6–20 days). The mortality rate was higher among the Italians (245/921, 26.6%) than among the immigrants as a whole (33/258, 12.8%) (p < 0.001). However, the mortality rate was higher among the immigrants from Latin America (21%) than among those from Asia (8%), central-eastern Europe (8%) or Africa (6%) (p = 0.016), and this difference remained after adjusting for potential confounders (p = 0.028).
Figure 2A and B show the Kaplan–Meier and adjusted survival curves of the Italians and immigrants. The overall probability of COVID-19-related death within 30 days of hospital admission was higher among the Italians: 24%, 95 CI: 21–27% vs 11%, 95 CI: 8–15%.; however, after adjusting for age, biological sex, time from symptom onset, obesity, and disease severity upon hospital admission, there was no between-group difference in 30-day mortality.
Figures 3A and B show the Kaplan–Meier and adjusted survival curves of the patients by region of origin. Latin Americans had the second highest probability of dying within 30 days of hospital admission (17%, 95 CI: 10–25%) but, after adjusting for age, biological sex, time from symptom onset, obesity, and disease severity upon hospital admission, it was the highest.
Uni- and multivariable Cox proportional hazard models assessing the effect of immigrant status and region of origin on the risk of COVID-19-related death
Table 3 shows the results of the uni- and multivariable analyses of the factors associated with COVID-19-related death.
The crude risk of COVID-19-related death among the immigrants was lower than among the Italians (HR 0.43, 95% CI 0.30–0.63; p < 0.0001). Moreover, the risk of COVID-19-related death among the immigrants from Africa (HR 0.20, 95% CI 0.06–0.63; p = 0.006), Asia (HR 0.28, 95% CI 0.12–0.63; p = 0.002), and central/eastern Europe (HR 0.27, 95% CI 0.09–0.84; p = 0.024) was lower than that of the Italians, whose risk was not significantly different from that of the Latin Americans (HR 0.74, 95% CI 0.47–1.15; p = 0.183) (Table 4).
However, when the Cox model was adjusted for possible confounders, there was no significant difference in the risk of death between the immigrants and the Italians (adjusted HR [aHR] 1.04, 95% CI 0.70–1.55; p = 0.831). Moreover, being of Latin American origin was independently associated with an increased risk of COVID-19-related death (aHR vs Italians 1.95, 95% CI 1.17–3.23; p = 0.010). The multivariable analyses also confirmed that age (aHR 1.07 per 1 year more, 95% CI 1.06–1.08; p < 0.0001), male biological sex (aHR: 1.46, 95% CI 1.12–1.92; p = 0.006), obesity (aHR: 1.64, 95% CI 1.23–2.20; p = 0.001), and disease severity upon hospital admission (severe disease (HR 3.76, 95% CI 1.78–7.93; p = 0.001; critical disease: aHR 8.52, 95% CI 4.09–17.76; p < 0.0001) were all independently associated with a higher risk of COVID-19-related death.
The integrated AUC-ROC values of the final model were 0.828 (Italians vs immigrants as a whole) and 0.824 (Italians vs immigrants stratified on the basis of their region of origin), and the GVIF values did not indicate the presence of multi-collinearity among the independent variables included in the final model.