Letter to the Editor: Chest CT and RT-PCR: radiologists’ experience in the diagnosis of COVID-19 in China

by Ruili Li, Guangxue Liu, Xiaochun Zhang, Hongjun Li (zxcylxyr@163.com, lihongjun00113@126.com)

Dear Editor,

In December 2019, corona virus disease (COVID-19) initially occurred in Wuhan, China, which was associated with the infection of severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2), and the number of infected people increased rapidly in local and spread all over the country [1]. After adopting a strict infection control (including isolation and quarantine), the COVID-19 epidemic in China had been preliminarily controlled in early March, and the number of new infected patients was gradually decreasing. However, COVID-19 cases increased rapidly in countries outside of China and caused an pandemic in world widely, including Italy, Iran, Spain, Germany, and France, at the same time, United Kingdom and United States were also threatened by SARS-CoV-2 [2].

The clinical diagnosis of suspected cases depends on the combination of epidemiological, clinical, laboratory (reduced lymphocytes count) and CT findings [1, 3]. In China, a definitive diagnosis requires the positive results in reverse transcription-polymerase chain reaction (RT-PCR) assay for SARS-CoV-2 [4]. However, many Chinese first-line radiologists found that there was some difference between chest CT findings and the results of RT-PCR assay for the throat/nasal swabs. Some suspected cases with CT features of acute pneumonia showed negative results of RT-PCR at initial, and positive results could be observed in repeated assays subsequently. One possible explanation was the limited sensitivity of existing laboratory testing methods or low viral load concentrations which exceeded the limit of detection [5-9]. In a retrospective analysis of 51 patients, the sensitivity for COVID-19 infection of CT (98%) was significantly higher than that of RT-PCR assay (71%) [7]. Moreover, two recent studies reported that the range of ground glass density patches on the chest CT of COVID-19 patients increased in a short-term follow-up, which suggested the disease progressed [10, 11]. Therefore, excluding COVID-19 with only once RT-PCR assay may lead to delay the diagnosis and treatment in a certain extent, and affect the control and prevention of COVID-19 pandemic eventually.

In order to improve diagnosis and treatment, we first drew up the “Guidelines for Imaging Diagnosis of COVID-19” on January 30, 2020 [12], and brought forward our suggestion to the health policy maker on February 3, 2020. We proposed that chest CT examination should be recommended as an imaging marker for clinical diagnosis in major epidemic areas (such as Wuhan), and the diagnosis flow chart was shown in Figure 1. Our views are widely supported by many radiologists in China and have caused widespread concern. On February 4, 2020, the National Health Committee of China (NHC) temporarily added chest CT as a complementary criterion of clinical diagnosis for COVID-19 in Hubei Province in the 5th edition clinical guidelines [13]. Suspected cases with CT features of pneumonia should be regarded as clinically diagnosed cases and treated immediately. This measure has improved and speed up the standardization of treatment for COVID-19 patients, and is beneficial to the control of the entire epidemic.

On February 13, 2020, Hubei Province announced that the number of clinically diagnosed cases was counted as the number of confirmed patients, which was a reply to our suggestion and an affirmation of CT imaging diagnosis. From 00:00 to 24:00 on February 12, 2020, Hubei Province reported 14,840 new infections of COVID-19 (including clinically diagnosed cases, 13,332) [14]. On February 3, 2020, several mobile cabin hospitals (Fangcang hospital, temporary healthcare units with multi-beds) for infected patients with mild symptoms were built up in Wuhan to relieve the pressure on the healthcare system as the number of COVID-19 cases increases. The mild patients can be better and more efficiently treated in cabin hospitals rather than isolation at home or in general hospitals crowded with severe patients.

Controlling the source of infection and treating patients as earlier as possible are the key to prevent the pandemic. Chest CT played a crucial role in the early diagnosis and evaluation of COVID-19 due to its sensitivity. RT-PCR assay for SARS-CoV-2 still is the gold standard for the diagnosis, due to the possible false positive result of chest CT. However, prevention the rapidly spreading of COVID-19 has the top priority at present. A possible diagnosis of COVID-19 and timely isolation and treatment should be considered after chest CT findings with acute pneumonia and excluding the other common respiratory pathogens, which will benefit the emergency infectious disease control.

Funding

This study is supported by the National Natural Science Foundation of China (No: 81771806, 61936013), Peking University Medicine Seed Fund for Interdisciplinary Research (No: BMU2018MX027), and Capital medical university research and incubation funding (No: PYZ19162). The sponsors had no role in the investigation of issues, data collection, decision to publish, or preparation of this manuscript. The authors declare their independence.

Acknowledgments

We are grateful to all persons who are fighting on the front lines against COVID-19. We also thank the medical personal of Beijing Youan Hospital and Wuhan Zhongnan Hospital for their efforts.