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.