Discussion:
The global outbreak of novel coronavirus 2019 (COVID-19) has been a matter of international concern due to the fast spread of the disease (25). During the initial phase of COVID-19 outbreak, the diagnosis of the disease was complicated due to the diversity of symptoms and imaging results as well as the severity of disease at the time of presentation (26). Therefore, it is very essential to precisely diagnose the patients suspected with COVID-19 infection for appropriate isolation or treatment. Currently, the RT-PCR amplification of viral DNA is considered as the “gold standard”. However, initial RT-PCR is not always positive in a patients with COVID-19 infection (16, 27). In this case, chest CT images could play an important role to detect the lesions of pulmonary parenchyma in the patients suspected with COVID-19 infection. Nevertheless, it does not mean that the abnormalities of CT images could be observed in COVID-19 infection while the initial RT-PCR is positive or negative (16, 27, 28).
Previous studies have suggested that a false-negative rRT-PCR result may occur in some COVID-19 patients (29, 30). False-negative results may be a function of various factors such as human errors when following the diagnostic kit protocol, the sensitivity of reagents, the site and method of specimen sampling and collection times (31).
In Yang et al. study, the total positive rate of RT-PCR for throat swab samples was reported to be about 30-60% at initial presentation despite limitations of sample collection, transportation, and kit performance. In this study, all patients were evaluated for clinical manifestations and radiological examination (32). One of the studies in Wuhan revealed that a considerable ratio of COVID-19 patients may have had an initial negative rRT-PCR result and that the primarily positive patients had a higher tendency to progress to severe cases. In this study, it was stated that patients with negative rRT-PCR who presented with typical clinical manifestations should not be ignored and suggested that PCR should be repeated (33).
In our study, we also examined the date of symptoms’ onset before admission to the hospital and no significant differences were observed between PCR positive and PCR negative groups. Yang et al. revealed that the sputum sample collected during 8-14 days showed a higher positive qPCR rate than the nasal and throat swabs samples in both severe and mild cases. The positive qPCR rate of throat samples decreased a few days after the onset of symptoms to hospitalization and performing PCR tests. The likelihood of positive throat samples test and symptoms decreased after 15 days (32).
In our study, patients were hospitalized based on clinical manifestations, the results of laboratory tests and positive CT scan corresponding to COVID-19, and RT-PCR test result were ready after 48 hours. We performed RT-PCR on oropharyngeal specimens. In this research, we found 67.6% PCR positive results, a percentage that may be due to the same test conditions, including the operator performing the test, sampling method, diagnostic kit, etc. for all samples. We detected a slight difference between positive and negative RT-PCR patients in terms of clinical and laboratory findings, initial vital signs and comorbidity. Therefore, patients with negative RT-PCR should not be discharged from hospital, especially when presenting similar clinical manifestations to positive RT-PCR patients. It can be strange that those negative RT-PCR results could be problematic.
This study has a number of limitations. First, it was not possible to repeat negative RT-PCR tests due to shortcomings such as the lack of laboratory testing capacity, insufficient staff and limited number of diagnostic kits. Second, RT- PCR tests were performed only on hospitalized patients and did not assess COVID-19 suspects who had been recommended home quarantine and rest. Third, the physicians judged the patient’s hospitalization requirement based on clinical symptoms and CT scan of lungs because it was not possible to perform a rapid RT-PCR test at first. Therefore, we had no patients with negative CT scan and positive RT-PCR. Fourth, incomplete medical records of a few patients due to the high number of patients’ admission to the hospital emergency ward, insufficient number of physicians and nurses to complete the history as well as the patients’ inability to express their history were another limitation of the present research.