Diagnostic value of chest CT in outpatient for COVID-19 compare with RT-PCR

Objectives The pneumonia caused by the 2019 novel coronavirus recently break out in Wuhan, China, and was named as COVID-19. With the spread of the disease, it bring numbers of casualties,so now we need a way could fast and accuracy diagnose the disease.This paper aims to compare two way for diagnose COVID-19 in outpatient :Chest CT and RT-PCR. The study picked 248 patients who treated in fever clinical of GanZhou people's hospital,their complete clinical and imaging data were analysed retrospectively.Epidemiological data,symoptoms,laboratory test results include RT-PCR and the CT results include CT features,lesion location,lesion distribution of suspected COVID-19 infected patients were gathered.


Introduction
In the end of 2019, an outbreak of serious and highly infectious pneumonia in Wuhan was caused by a new corona virus infection named COVID-19 (Corona Virus Disease 2019). By February 18, 2020,there are more than 70,000 con rmed cases with more than 1700 deaths [1,2]. From the current epidemiological ndings, the main characteristics of COVID-19: 1, It is mainly spread by respiratory droplets and close contact., aerosol transmission is possible in speci c environment, and fecal-mouth is still to be determined. 2, The population was generally susceptible (R0 about 3.77), the incubation period ranging from 1 to 14 days, mostly 3 to 7 days. 3, Clinical symptoms varied, with fever (98.6%), fatigue (69.6%), dry cough (59.4%) as the main manifestations, other clinical symptoms include anorexia, myalgia, pharyngitis, dyspnea, runny nose, diarrhea, etc., or no obvious symptoms. 4, Effective drugs and virus vaccines are still in the research and development stage, the main treatment methods are symptomatic treatment, prevention and control of the situation is grim. The diagnosis of COVID-19 is based on contact history, clinical symptoms and laboratory examination such as WBC,procalcitonin(PCT), Creactive protein(CRP), lymphocyte count and real-time polymerase chain reaction (RT-PCR). RT-PCR is standard of the disease and widely applicate [3]. Recently, Xie reported 5/167(3%) patients who had negative RT-PCR for COVID-19 at initial presentation despite chest CT ndings typical of viral pneumonia [4].
The purpose of this study was to compare two way for diagnose COVID-19 in outpatient: Chest CT and RT-PCR.

Patients
To avoid spread of COVID-19 and protect the medical staffs,our hospital sets the fever clinical and asks all the fevered patients treated in it. The study comprised 248 patients who presented with a history of 1) travel or residential history in Wuhan or local endemic areas or contact with individuals with fever or respiratory symptoms from these areas within 14 days.or 2) had fever or acute respiratory symptoms of unknown cause treated from 1 January 2020, to 29 February 2020, with complete medical records.All the patients'data were obtained through telephone communication with the doctor in charge or the patient and the patient's family. All the clinic doctors received training for how to sandard sampling, got know typical CT manifestations.

Examination equipment and methods
During this period,nonconstrast chest CT(A GE Discovery CT 750 HD CT system,slice thickness,5 mm) and RT-PCR(Shanghai ZJ BI) was performed for these patients. All the laboratory examination result also recorded.Typical and atypical chest CT ndings were recorded according to CT features previously described for COVD-19. Among all the upper respiratory sampling methods, oropharyngeal aspirate (OPS) had a higher positive rate within 2 weeks of symptom onset, and OPS was the least harmful to medical staff during sampling,so we use OPS swab sample for RT-PCR. [5,6] Data collection and Statistical analysis Epidemiological data,symoptoms,laboratory test results include RT-PCR,and the CT results of suspected COVID-19 infected patients were analysed retrospectively. SPSS19 .0 software was used for statistical analysis.

Discussion
Coronaviruses are a family of viruses widely found in nature, and the newly discovered COVID-19 is the seventh known coronavirus to infect humans [7]. Due to the unpredictability, strong transmissibility and great harmfulness of novel coronavirus, it has brought great harm to the health and economy of people all over the country and even the world [8]. Early screening, isolation and treatment is the key to the prevention and control of COVID-19, Positive RT-PCR is the gold standard of diagnosis [9].Since sampling of the upper respiratory tract is the most convenient and relatively comfortable method for patients,so we usual use it in outpatient department. But at the same time, nucleic acid detection is also affected by many other factors, such as sample quality, patient infection cycle, collection time, experimental factors and kit performance [10,11].In the outpatient, the conditions and equipment are limited,we can't sampling lower respiratory samples [sputum, bronchoalveolar lavage uid (BAL)].As you know outpatient is the rst line in this epidemic, accurate and quick diagnosis is very important. We could admite the sick patient to the hospital in time, avoid the epidermic futher expend. But the sensitivity of RT-PCR is not attained the clinical demand, more evidence about the clinical value of using chest CT in the diagnostic assessment of this disease will be available for clinicians to diagnosis of patients with COVID-19 [12,13].
Based on the results of this study we recommend: (1) All patients with typical clinical symptoms need a lung CT examination.
Patients with typical lung signs should be admit to the hospital for quarantine,receive futher examination and treatment. For

Conclusions
The sensitivity and accuracy of chest CT is better than nucleic acid detection for diagnosis of COVID-19,so we think chest CT play a more important role in outpatient.  Examples of typical chest CT ndings compatible with COVID-19 pneumonia. Chest CT shows extensive ground-glass opacities, consolidation, spider web pattern and interlobular septal thickening.