The COVID-19 pandemic brought many changes to the medical environment and processes of emergency departments (EDs). The total number of patients visiting the ED decreased significantly during the COVID-19 period, although the proportion of admitted patients increased in one study [1]. The COVID-19 pandemic increased the number of people leaving emergency rooms without being seen [2,3]. One study found that ED length of stay (LOS) was significantly longer during the COVID-19 period than before, despite a smaller volume of patients in the COVID-19 period [4]. The time to provide medical care to patients was delayed due to concerns about the spread of COVID-19 in hospitals [5]. Admission to most Korean hospitals was allowed only after confirming negative COVID-19 polymerase chain reaction (PCR) results and isolating accordingly. In one study, PCR-based testing on admission was an effective component of COVID-19 diagnosis and reduced risk of in-hospital transmission [6]. During the pandemic, there were many efforts to decrease the time to a COVID-19 test result [7,8]. Nevertheless, the ED LOS for patients admitted through the ED continued to increase [4].

A number of studies have shown that the longer the LOS in the ED, the worse the patient’s outcome, because longer ED LOS often involves delay of timely and appropriate interventions, which increases condition severity and risk for poor outcomes [9–13]. Such treatment delays might have contributed to the development of time-dependent complications and subsequently higher intensive care unit (ICU) or general ward (GW) mortality [14]. For situations requiring urgent treatment, admission delays may worsen patient prognosis [15,16].

We hypothesized that COVID-19 had negative effects on patient prognosis. The purpose of this study was to determine whether there was a difference in in-hospital mortality among patients admitted through the ED before and after the COVID-19 pandemic.

After adjusting for confounding variables, in-hospital mortality of patients admitted through the ED in the after-COVID-19 period was significantly higher than before the COVID-19 period. Although we could not compare severity between the two groups, there were no differences in the proportion of vasopressor or CRRT use before and after COVID-19. Rather, the proportion of patients receiving mechanical ventilation was significantly lower after COVID-19 than before, although in-hospital mortality was higher. The number of patients admitted to the ICU from the ED did not differ significantly before and after COVID-19.

We investigated changes between the before-COVID-19 and after-COVID-19 periods for ED LOS and prognosis of patients admitted through the ED. Several studies have reported an association between ED LOS and patient prognosis. Furthermore, associations between COVID-19 and ED LOS have been reported [1,4,17–19]. The sample size of this study is relatively large. Another strength of our study is that the treatment protocol was consistent for all patients given the single-center study design. Although severity could not be directly compared between the time points, the variables that could affect patient prognosis did not show a statistical difference between the two periods, and some variables with a difference did not appear to have a clinical effect.

There are several possible explanations for a patient’s poor prognosis during the after-COVID-19 period. Since the spread of COVID-19, more people are staying at home to maintain social distance. Meanwhile, the numbers of remote treatments and postponed scheduled treatments are increasing [20]. In addition to the shift toward remote treatment, COVID-19 has also impacted hospital admissions and visits unrelated to COVID-19 itself [21]. Studies in Spain and Italy have shown a reduction in hospitalizations and procedures related to myocardial infarction and acute coronary syndrome [22,23]. Thus, it is possible that these patient did not receive timely treatment before their conditions worsened, and the severity was already high when patients arrived at the ED. In addition, as shown in an out-of-hospital cardiac arrest study, the longer the prehospital transport time, the worse the patient’s treatment outcome [24]. In patients who visited the ED for other conditions, the delay in prehospital transport due to lack of isolation rooms might be the cause of increased in-hospital mortality. However, our data do not have information about prehospital transport time and cannot be verified. Changes in the number and proportion of patients by hospital department before and after COVID-19 may also be associated with an increase in in-hospital mortality after COVID-19. Compared with the before-COVID-19 period, the number and proportion of internal medicine and general surgery inpatients increased after the COVID-19 pandemic. However, it is difficult to conclude that the increase in the number of patients admitted to internal medicine and general surgery in the after-COVID-19 period is the cause of the increase in in-hospital mortality without adjustment for severity or diagnosis. Increased workload, lack of rest, and fear of infection or infecting others were observed in the after-COVID-19 period, especially among healthcare workers in the ED and ICU [25]. These factors might adversely affect in-hospital patient care in the after-COVID-19 period.

Several studies have shown that ED crowding and long ED LOS are associated with poor patient prognosis, hospital LOS, and cost [10]. ED crowding increases the waiting time to enter the ED, which delays the final diagnostic test or definitive treatment. In our hospital, patients had to wait in the ED until their PCR test results were confirmed, and due to a lack of isolation beds, ED crowding increased. The wait time from ED arrival to meet with medical staff also seemed to increase, leading to an increased ED LOS. Similar to another study, the number of patients who left the ED without being seen was significantly higher after COVID-19 in our hospital [3]. A main reason for leaving without being seen was the long waiting time from arrival to ED entrance. In our hospital, people arrived at the ED but were often not registered immediately if there were many waiting patients. In these instances, although not specifically calculated, it is estimated that the actual ED LOS was longer in the period after COVID-19. Frequent shifts between nurses and doctors can impede continuity of care and prioritize new patients, resulting in poor-quality care. PCR testing is essential for COVID-19 diagnosis, and as the number of confirmed COVID-19 patients in Korea increased, most Korean hospitals were admitting patients to the GW or ICU after confirming their test results [26]. One study showed that the time spent in the ED increased after COVID-19 compared with before COVID-19 [27]. In that study, it was suggested that the cause of the increase in LOS and ED crowding was the time needed to obtain results from the COVID-19 PCR test. A study that analyzed changes in elderly patients before and after COVID-19 onset reported that the number of ED visits decreased after COVID-19, but that mortality increased, possibly due to the screening process or testing to differentiate between infected and noninfected patients [28].

This study has several limitations. First, because this is a single-center retrospective analysis, our results cannot be generalized to other medical institutions. Nevertheless, this single-center study has the advantage of a consistent treatment protocol, limiting the effect of treatment on patient outcomes. There is no international guideline stating that PCR results of all patients should be verified prior to admission from the ED to a ward or ICU. Therefore, it is not appropriate to generalize our findings regarding increased ED LOS to other medical institutions and other countries. Second, severity scores that could affect patient prognosis, such as sequential organ failure assessment score or acute physiology and chronic health evaluation scores, could not be analyzed. However, underlying disease, vital signs, and blood test results that might affect patient prognosis showed no clinically significant difference between the two groups. Moreover, proportions of vasopressor and CRRT use were not significantly different between the before-COVID-19 and after-COVID-19 periods. Considering that the frequency of mechanical ventilation has decreased since COVID-19, in-hospital mortality has not seemed to increase due to differences in severity. Finally, it cannot be concluded that an increase in ED LOS leads to an increase in in-hospital mortality. Variables that could affect a patient’s in-hospital mortality were adjusted through multivariable analysis; however, it is uncertain whether the adjustment is sufficient due to the possibility of unmeasured confounders. In addition, we cannot infer causality with our findings.

In conclusion, the after-COVID-19 period was significantly associated with increased in-hospital mortality among patients hospitalized via the ED. This study suggests that the outcome of ED patients might worsen during the COVID-19 pandemic, but further research is required about what factors affected the outcome.