New Crown Pneumonia Is Difficult To Track: Can The Image CT Be Standard?

"Do not superstitious nucleic acid testing, and strongly recommend CT imaging as the main basis for 2019-nCoV pneumonia." A circle of friends of Professor Zhang Xiaochun, Professor of imaging at Zhongnan Hospital of Wuhan University, has triggered a heated debate. Professor Zhang Xiaochun pointed out in his circle of friends: "at present, the incidence of family clustering is increasing in Wuhan, and most of them are hidden from the onset. Once or even a few times, the nucleic acid is negative, without any clinical symptoms, such as taking the way of home observation, which will inevitably lead to further spread of the epidemic."

According to the office of the national health and Health Committee issued in February 3rd, the new pneumonia diagnosis and treatment plan for new coronavirus infection (trial version fifth) issued the diagnostic criteria as follows: suspected cases, with one of the following etiological evidence: first, respiratory tract specimens or blood samples were detected by real-time fluorescent RT-PCR for new coronavirus nucleic acid positive; Two, respiratory tract specimens or blood samples are highly homologous to known new coronaviruses.

In February 3rd, at the press conference of the Information Office of the State Council, Tian Yulong, chief engineer of the Ministry of industry and commerce, said that in February 1st, the daily output of reagents had reached 773 thousand people, 40 times that of suspected patients, and basically met the requirements. In fact, since January 24th, the State Food and Drug Administration (FDA) has opened a fast examination and approval channel for some new coronavirus detection kits manufacturers, the problem of capacity and supply of new coronavirus detection kits has been significantly improved.

However, the problem of "diagnosis is difficult" is restricted by the restrictions caused by laboratory and laboratory personnel. After testing the capacity of the kit, the test capability can not meet the actual needs of Wuhan.

Is CT imaging diagnosis of pneumonia feasible? What are the advantages of nucleic acid test and CT imaging?

The "gold standard" of the kit is under pressure.

As a "gold standard", the reagent kit is still difficult to solve in the face of the reality of large-scale outbreaks.

The diagnosis of new coronavirus depends on only two methods. One is PCR (polymerase chain reaction) detection kit and one gene sequencing technology, but the technology of gene sequencing is relatively expensive and the detection efficiency is limited.

PCR is the process of nucleic acid amplification, which can be confirmed only by trace nucleic acid. However, PCR is susceptible to contamination of particulates and liquids in the air. It requires a high level of protection for the testing laboratories. It is necessary to have a special laboratory partition to complete the four experimental processes, such as reagent preparation, sample processing, nucleic acid amplification and product analysis, in order to ensure the accuracy and effectiveness of the test results.

At present, Wuhan is in line with the protection requirements, and the biological laboratory with detection ability is still relatively tense. The Wuhan Health Protection Commission disclosed in a notice released in January 23rd that only more than 200 samples could be detected per day before January 22nd.

In January 22nd, after obtaining the consent of the higher authorities, Wuhan only designated the designated hospitals for treatment, hospitals for the diagnosis and treatment of fever, the city's centers for Disease Control and prevention, and other biosafety laboratories with corresponding protection levels to carry out the detection of pathogenic nucleic acids in the relevant samples. After the whole operation, the detection capacity is expected to reach nearly 2000 copies per day.

Although laboratories and hospitals with testing capabilities in Wuhan are all at full load, it is still difficult to fully meet the testing needs. From 0 to 24 February 3rd, the number of suspected cases increased to 3260 in Hubei Province, which exceeded the upper limit of previous detection.

In addition, the detection of nucleic acid kit also has the possibility of missed detection and wrong examination. The diagnostic criteria are too harsh, confined to nucleic acid positivity (the clinical discovery rate is not guaranteed, and many cases need to be repeated), leading to a large number of highly contagious suspected cases which can not be isolated.

In vitro testing, the industry has revealed that one of the difficulties of nucleic acid kit detection is sample collection. "Now the biggest problem of nucleic acid detection is the collection of specimens. The diagnosis of new crown has its particularity. It is mainly due to the early symptoms of asymptomatic or mild diseases. The throat swabs from upper respiratory tract are easy to be missed, and the lower respiratory tract samples are not convenient to sample.

As for the defects in nucleic acid testing, the test related person said: "any product can not be 100% perfect at the beginning of research and development and at the beginning of its application. There is usually a process of continuous improvement, continuous improvement and continuous improvement. Just because of the quality of the reagent, it is unreasonable to conclude that using CT instead of nucleic acid detection.

CT imaging controversy

In Wuhan, is the current detection of nucleic acid kit deficient, can it help diagnose and screen isolation cases based on clinical CT images?

In fact, the identification of new pneumonia through CT images is not just a voice of Professor Zhang Xiaochun. A doctor in a hospital in Wuhan bluntly pointed out that for today's Wuhan, "it is recommended to amend the diagnostic criteria, epidemiological history + viral pneumonia (no serious epidemiological history is needed in severe epidemic areas)", that is, clinically confirmed cases, all need to be transferred to designated hospitals for isolation treatment.

Meanwhile, the radiology department of Wuhan Union Hospital and the radiology department of Wuhan Jin Yin Tan Hospital, in January 22nd, published a preliminary report on the imaging findings of 19-nCoV pneumonia in Wuhan, and discussed the feasibility of identifying and diagnosing new pneumonia through clinical imaging. According to the report, "2019-nCoV pneumonia is characterized by various imaging manifestations. CT is easy to detect early grind lesions. Chest X-ray can detect lesions of lung consolidation, bedside examination and curative effect evaluation."

But the report also clearly pointed out that the new pneumonia is not easy to distinguish from other kinds of pneumonia. It needs to be identified by other personal information. 2019-nCoV pneumonia is overlapped with other viral pneumonia and organic pneumonia and eosinophilic pneumonia. Combined with patient contact history, tourism history, first symptom and laboratory examination, it helps to identify.

In addition to the confirmation of the "golden standard", whether there is any image CT, there are also some objections from the test. Inspectors said: "imaging as the main basis, this loss we have eaten in SARS, the rate of misdiagnosis is very high, and CT image detection cross infection risk. At the same time, if Wuhan is to be included in the diagnostic standard, the CT machine in CT is virtually impossible to meet the demand. Using CT images as an isolation criterion rather than a diagnostic standard seems to be more consistent with the actual situation in Wuhan. CT is the early screening of suspected patients, rather than early diagnosis, reduce the isolation criteria to reduce the possibility of transmission of suspected cases. "

At the press conference of the national health and Health Committee in February 4th, Li Xingwang, a member of the national medical expert group and the chief expert of infectious disease diagnosis and treatment center of Beijing Ditan Hospital, also pointed out that in the published versions of the diagnosis and treatment plan, CT imaging examination has always been one of the diagnostic criteria, but the final diagnosis of infectious diseases still depends on etiology, such as nucleic acid determination. However, the suspected cases reflected in the imaging should be sent to the designated hospitals in time for timely treatment.

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