This multicenter study indicated that from the 1357 COVID-19 patients, survived from the first admission, 99 individuals (7.29%), were readmitted. The number of underling diseases and being treated with GC during hospitalization were associated with a significantly higher rate of readmission.
Rate of readmission in this study was comparable with that of the studies from the other countries(3, 11). Some diseases like HTN, CAD, CKD, COPD, CVA, and Cancer increased the rate of readmission; however, their effect vanished after multivariate adjustment. Adjustment was done for the main contributing factors smoking, opium use, the number of underlying disease, ICU admission, and chest CT infiltration. After multivariate adjustment, GC therapy and the number of underlying disease ( > = 1) were associated with an increase in the rate of readmission.
The association between COVID-19 readmission and various underlying diseases has been previously reported in different studies. HTN, COPD, and pulmonary fibrosis have been frequently associated with a higher risk of readmission(7, 12). A Spanish study showed that immunocompromised patients were also more likely to be readmitted(11). Moreover, some studies, including ours, showed the higher number of comorbidities is associated with a higher rate of readmission(3, 9). In line with our results, a large Koran study showed higher risk of readmission in patients with some underlying diseases like DM, HTN, Dementia and those who had at least one underlying disease(3).
The reason why GC therapy increases readmission rate, is probably due to the fact that patients who received GC, had more severe pulmonary involvement and less oxygen saturation than patients treated with oral antiviral therapy (according to Iranian national protocol for the treatment of COVID19 (10). As it is recommended in many international guidelines, we do not start treatment with GC until oxygen saturation is decreased. As a result, patients who are candidates for treating with corticosteroids have more pulmonary involvement. Perhaps The greater risk of readmission in patients treated with GC is related to more pulmonary involvement.
In contrast of our results, prescribing GC did not increase the rate of readmission in Spanish study; This difference may be related to the time of prescription; we considered prescription of GC during the hospitalization while they included only the patients who discharged with GC (11).
The univariate analysis showed that smoking or opium use were risk factors for hospital readmission. This effect might be mediated by various factors such as socioeconomic condition, employment, education, social support, and social determinants of health(13).
As shown in previous studies, pneumonia and respiratory distress were the most common causes of readmission (9). Hospital readmitted patients with COVID-19 has not yet been widely evaluated, however, assessing the causes of readmission is necessary to identify preventable causes (9).
According to this study, patients with a medical condition have higher risk of readmission than patients with no underlying disease and this is justifying some therapeutic guidelines (like Iranian national protocol) of COVID-19 that recommends patients with at least one underlying disease were considered as the priority for hospitalization. Therefore, it seems that in the emergency department, patients with underlying diseases should be given priority to diagnostic and therapeutic procedures and also in allocation of the facilities. Also, related to use of medical treatment, the patients who received GC had a higher rate of readmission versus to the patients received Kaletra, HCQ, and Sofosbuvir. Similar to our study, the Korean one showed lower rate of readmission in patients who were treated with HCQ and Kaletra and it may be due to milder type of the disease in patients treated with oral agents(3). Similar to ours, an American study showed the type of ventilation and intubation rate had no difference between readmitted and non-readmitted patients(9).
We showed no difference in sex, age and the duration of the admission in two groups; but a Korean study showed a higher rate of readmission in male and older patients and also in those with shorter length of staying at the first admission in readmitted group; These differences may be related to the larger number of study population in the Korean one (7590 patients) compared with ours (1357 patients) (3).
Limitations and strength
Obtaining and gathering information from several tertiary centers and including a relatively large number of patients were the strength of our study. However, there are some limitations. First of all, we could not provide more detailed information such as clinical characteristics of the patients. A lot of missing data were detected in records. Moreover, this study was conducted at the middle of the pandemic and the characteristics might be differing during the pandemic.