The high volume of patients admitted during the SARS-CoV-2 pandemic has an independent harmful impact on in-hospital mortality from COVID-19

Abstract

Background: During the Coronavirus disease 2019 (COVID-19) pandemic, advanced health systems have come under pressure by the unprecedented high volume of patients needing urgent care. The impact on mortality of this "patients' burden" has not been determined.

Methods and findings: Through retrieval of administrative data from a large referral hospital of Northern Italy, we determined Aalen-Johansen cumulative incidence curves to describe the in-hospital mortality, stratified by fixed covariates. Age- and sex-adjusted Cox models were used to quantify the effect on mortality of variables deemed to reflect the stress on the hospital system, namely the time-dependent number of daily admissions and of total hospitalized patients, and the calendar period. Of the 1225 subjects hospitalized for COVID-19 between February 20 and May 13, 283 died (30-day mortality rate 24%) after a median follow-up of 14 days (interquartile range 5-19). Hospitalizations increased progressively until a peak of 465 subjects on March 26, then declined. The risk of death, adjusted for age and sex, increased for a higher number of daily admissions (adjusted hazard ratio [AHR] per an incremental daily admission of 10 patients: 1.13, 95% Confidence Intervals [CI] 1.05-1.22, p = 0.0014), and for a higher total number of hospitalized patients (AHR per an increase of 50 patients in the total number of hospitalized subjects: 1.11, 95%CI 1.04-1.17, p = 0.0004), while was lower for the calendar period after the peak (AHR 0.56, 95%CI 0.43-0.72, p<0.0001). A validation was conducted on a dataset from another hospital where 500 subjects were hospitalized for COVID-19 in the same period. Figures were consistent in terms of impact of daily admissions, daily census, and calendar period on in-hospital mortality.

Conclusions: The pressure of a high volume of severely ill patients suffering from COVID-19 has a measurable independent impact on in-hospital mortality.

Fig 1. Distribution of inpatients over time at San Gerardo Hospital.

The number of daily admissions (gray) increased progressively until a peak of 58 patients on March 18, and the number of total hospitalized patients (black) peaked on March 26, with 465 subjects.

Fig 2. Crude-incidence curves of in-hospital mortality at San Gerardo Hospital, stratified by age strata (A) and sex (B).

Fig 3. Crude-incidence curves of in-hospital mortality at San Gerardo Hospital, stratified by “hospital stress” variables.

Variables of “hospital stress” are considered as fixed variables measured at patient hospital admission. A: number of daily admissions; B: total daily census; C: calendar period before or after the peak.

Fig 4. Risk of death in the time-dependent Cox model by hospital stress variables.

Circles and bars represent the age- and sex-adjusted hazard ratios (HR) and the corresponding 95% Confidence Intervals of death, according to A) daily number of admissions (per increase of 10 units), B) total daily census (per increase of 50 units, C) calendar period (after versus before the peak). On the left: San Gerardo Hospital. On the right: Bassini Hospital.