Chest CT for Typical 2019-nCoV Pneumonia: Relationship to Negative RT-PCR Testing

Abstract

Introduction

In December 2019, an outbreak of 2019-nCoV pneumonia began in Wuhan (Hubei, China) and spread rapidly [1]. Without a therapeutic vaccine or specific antiviral drugs, early detection and isolation becomes essential against novel coronavirus. The use of chest computed tomography (CT) as a screening tool for patients with suspected 2019-nCoV not well understood. In our experience, some patients with likely 2019-nCoV infection may have initial negative reverse transcriptase (RT) polymerase chain reaction (PCR) results. Reasons for false negative RT-PCR may include insufficient cellular material for detection and improper extraction of nucleic acid from clinical materials.

The purpose of the study was to describe CT imaging features of five patients with initial negative or weakly positive RT-PCR results but high suspicion of 2019-nCoV infection.

Materials and methods

This study was approved by Medical Ethical Committee (Approved Number.2020002), which waived the requirement for patients’ informed consent referring to the CIOMS guideline.

Results

167 patients were evaluated; of these 5 (3%) patients initially had negative RT-PCR but positive chest CT with pattern consistent with viral pneumonia (figure 1). After positive CT findings, all patients were isolated for presumed 2019-nCoV pneumonia. Repeat swab testing and RT-PCR tests 2019-nCoV infection in all patients. In 7 patients (4%), CT was initially negative while RT-PCR was positive. In 155 patients (93%), both RT-PCR and CT were concordant for 2019-nCoV infection. Of the 5 patients with negative RT-PCR and positive CT at initial presentation, the median CT involvement score was 4. The highest CT involvement score was 14 while the minimum was 2.

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Figure 1:

Patient flowchart. Of 167 patients screened, 5 (3%) had negative RT-PCR results and chest CT findings compatible with 2019-nCoV pneumonia.

The description of 5 patients with positive CT and negative RT-PCR results are presented below:

• Patient 1: A 62-year-old male with recent travel history to Wuhan, China, the epicenter of the 2019-nCoV outbreak[5], was admitted to the hospital with fever and mild cough of 6 days duration. The chest CT showed multi-focal ground glass opacity (GGO) and parenchyma consolidation, predominantly involving subpleural regions of both lung (Figure 2). The CT involvement score was 14. During isolation for presumed 2019-nCoV pneumonia, the patient became dyspneic and developed type I respiratory failure five days after admission. The second swab test of 2019-nCoV was positive five days after CT scanning.
  

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  Figure 2:

  Chest CT imaging of patient1.A-D, CT images show bilateral multifocal GGOs and mixed GGO and consolidation lesions. Traction bronchiectasis(fat arrow) and vascular enlargement are also presented (thin arrow).

• Patient 2: A 60-year-old male with fever of 39°C was referred for hospital evaluation. His wife had been previously diagnosed with 2019-nCoV pneumonia. His CT images showed multi-focal GGO and mixed consolidation that most appeared at peripheral area of lung. (Figure 3). The CT involvement score was 11. The first swab test was negative and the male patient was quarantined at home. Over the next week, multiple swab tests returned negative results but his symptom remained. On day 8, the swab test was positive and the patient was hospitalized for further treatment.
  

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  Figure 3:

  Chest CT imaging of patient 2. A-D, CT images showed multi-focal GGO and mixed consolidation that most appeared at peripheral area of both lungs. The CT involvement score was 11.

• Patient 3: A 25-year-old female appeared with cough, dizziness and debility but had no fever. Her RT-PCR results were weakly positive on the first swab test. Both her parents were diagnosed with 2019-nCoV pneumonia. She was quarantined at home. A second mouth swab test conducted the next day was negative, but a CT at that time that showed bilateral subpleural GGO indicating viral pneumonia (Figure 4). The CT involvement score was 4.Two days after CT examination, the third swab test result was positive for 2019-nCoV, confirming CT results.
  

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  Figure 4:

  Chest CT imaging of patient 3. A-D, CT images showed bilateral subpleural bandlike areas of GGO compatible with viral pneumonia.

• Patient 4: A 66-year-old male with ongoing fever was admitted to hospital. His social history was positive for close contact with an individual having confirmed 2019-nCoV pneumonia. A swab test and RT-PCR for 2019-nCoV was negative. CT scanning was performed at the same time and showed patchy GGOs in the subpleural regions of both lungs suggesting viral pneumonia. The CT involvement score was 3. The patient was kept under observation and home isolation. During the period of isolation (2 days after chest CT scanning), the swab test turned positive, confirming prior CT results.
• Patient 5: A 29-year-old male with onging fever was admitted to hospital. He had a travel history to Wuhan during the 2019-nCoV outbreak. A swab test and CT scanning were performed. The CT images showed multi-focal mixed GGO and parenchyma consolidation involving the subpleural regions of both lungs suspicious for viral pneumonia. The CT involvement score was 2. Two RT-PCT tests were both negativ and the patient was kept on home-isolation. A third swab test was positive 8 days after CT scanning. The patient was sent to hospital for isolated treatment.

Discussion

Based on clinical data obtained from the Radiology Quality Control Centre, Hunan province, we evaluated radiographic characteristics of 5 patients with confirmed 2019-nCoV infection and initial negative or weakly positive RT-PCR. All patients presented characteristic radiographic features of 2019-nCoV pneumonia from the first scan and then were confirmed by positive repeat swab test during the isolated observation or treatment. The review of these five cases suggested typical CT findings can help early screening suspected cases and may predict severe complications such as acute respiratory diseases.

According to current diagnostic criteria, laboratory examination such as swab test has become a standard and formative assessment for the diagnosis of 2019-nCoV infection [2]. However, the current laboratory test is time-consuming, and a shortage of supply test kits may not meet the needs of a growing infected population. RT-PCR testing for 2019-nCoV may be falsely negative due to laboratory error or insufficient viral material in the specimen.

Previous radiographic studies showed that the majority of cases had similar features on CT images, like GGO or mixed GGO and consolidation. 2019-nCoV pneumonia is likely to have a peripheral distribution with bilateral, multifocal lower lung involvement [6-8]. In the context of typical clinical presentation and exposure to other individuals with 2019-nCoV, CT features of viral pneumonia may be strongly suspicious for 2019-nCoV infection despite negative RT-PCR results. In these cases, repeat swab testing and patient isolation should be considered.

Acknowledgments

References