In this prospective study, the results of clinical, laboratory and radiological examinations were used to identify the factors associated with readmission. Diabetes, abnormal blood creatinine levels, lung involvement, and duration of first-time hospitalization were the most important predictors of readmission. The readmission rate was 3.1% for one week after discharge, 7.6% for one month after discharge, and 8.6% for two months after discharge.
In this study the rate of readmission at similar time intervals was consistent with other studies (9), in which readmission in the first week after discharge was between 2 and 4% (13, 14 22) and was reported 10% for two months after discharge (9). In the follow-up of 279 discharged patients in Rhode Island of the United States, 30 days after discharge, readmission rate was reported 6.7% (11). In a study done in Turkish study, 7.1% of discharged patients were readmitted (15). The readmission rate of 106,543 COVID-19 patients discharged from the hospital two months after discharge was 9% in the United States (9). Donnelly et al followed up 1,775 discharged patients in the United States and reported readmission in 20% of the patients two months after discharge (19). In another study, 10.3% of discharged patients were readmitted to hospital 80 days after discharge (23). However, in different findings in the Korean study, the readmission rate of the patients with COVID-19 after discharge was 4.3% (12) and in Spanish study, the readmission rate was 4.4% up to three weeks after discharge (10).
The median length of stay in hospitals for the first time was 4 days which was similar to the findings of previous studies in Iran (24, 25). A review of 52 studies estimated the median length of stay in hospitals about 5 days (26), which was similar to the median length of stay in New York hospitals performed on 5,700 patients (13). Length of stay was very different in Korean hospitals (17 days) (12). Also, in the present study, the median length of stay for readmitted and non-readmitted patients was 5 days (IQR: 3–9) and 4 days (IQR: 3–6), respectively, while in the Turkish study, the median length of stay in the patients was 4 days and 3 days, respectively (15).
In the Spanish study, the median length of stay in the readmitted patients with COVID-19 was lower than other patients (6 days vs. 9 days) (10). In a review of 7,590 patients admitted to Korean hospitals, the median length of stay was lower than other patients (10, 12), but since the median length of stay in the patients who were not readmitted was shorter than in readmission patients, most patients were likely to be discharged on time. Hospitalization of patients has some conditions which include the capacity of the medical system, the quality of care and the demand for hospital beds in the pandemic period (15, 16). Different quality of post-discharge care can also have consequences on its effective after the discharge and we should pay attention to it in analyzing the results (14, 23).
Old age and underlying disease, especially diabetes, were two important characteristics of patients who were readmitted. The odds ratio of readmission in the patients over 60 years and diabetics compared to the younger patients and free of underlying disease was 1.83 and 3.43 times higher, respectively. In a study by Jeon et al, the odds ratio of readmission in the patients over 65 years and underlying disease was 2.23 and 4.39, respectively (12). Wu and McGoogan (27) and another study (13) the odds ratio of readmission in elderly patients was higher than in other age groups. Underlying diseases, especially hypertension and diabetes, have also been confirmed in other COVID-19 studies (10, 11, 14, 15). As the response of immune cells to the corona virus decreases with age, so the virus may be able to stay in the body longer. COVID-19 and readmission complications in older patients increase (28), however these two factors may be strong predictors of readmission in hospitalized patients (29). Highly creatinine level in hospitalized patients was another predictor of the risk of readmission in the COVID-19 patients, so that a creatinine level greater than 1.2 mg/dl, the odds ratio of readmission was 2.15 times higher than in other COVID-19 patients. Patients with a history of ICU hospitalization had higher creatinine levels (23). Findings of previous studies on other diseases also consider creatinine level as an effective factor in hospital readmission of the COVID-19 patients (32 − 30).
In this study, more than 84% of the patients who were readmitted had abnormal chest CT scans. Also, most readmitted patients (64%) had a negative PCR test and the time interval between discharge and readmission was higher in the patients with a negative test than in patients with a positive test. This finding was consistent with the findings of previous studies that introduced abnormal chest imaging results as a predictor of readmission (12, 33), making it a suitable tool for managing COVID-19 patients (34–36). Also, the possibility of a false negative result in PCR test was reported in previous studies (34).