A 20-year-old woman, who showed no symptoms of the new coronavirus and had normal chest CT imaging results but ended up passing the infection to five of her relatives.
Ever since scientists have been asking if a person can have this infection and not be ill. The new case study offers decisive evidence that the virus can be spread asymptomatically, which could make efforts to curb the outbreak even more challenging, say experts.

The researchers of the current study are calling it the first documented case of transmission from an asymptomatic person with normal chest CT findings.

“A novel coronavirus has resulted in an ongoing outbreak of viral pneumonia in China. Person-to-person transmission has been demonstrated, but, to our knowledge, transmission of the novel coronavirus that causes coronavirus disease 2019 (COVID-19) from an asymptomatic carrier with normal chest computed tomography (CT) findings has not been reported,” say the researchers in their findings published in JAMA.

“One previous study reported an asymptomatic 10-year-old boy with COVID-19 infection, but he had abnormalities on chest CT. If the findings in this report of presumed transmission by an asymptomatic carrier are replicated, the prevention of COVID-19 infection would prove challenging. The mechanism by which asymptomatic carriers could acquire and transmit the coronavirus that causes COVID-19 requires further study,” says the team.

The team includes experts from Department of Medical Imaging, Henan Provincial People’s Hospital, China; Department of Radiology, Anyang Hospital of Traditional Chinese Medicine, China; Department of Radiology and Interventional, the Fifth People's Hospital of Anyang, China; Tianjin Medical University Cancer Institute and Hospital, China; and Li Ka Shing Faculty of Medicine, the University of Hong Kong, Hong Kong, China.

A previous report by the Chinese Centers for Disease Control and Prevention (CDC) -- which analyzed a total of 72,314 cases till February 11, 2020 -- found that 889 cases or 1.2% were asymptomatic.

The current research letter describes that patient 1 (the presumed asymptomatic carrier), a 20-year-old woman, lives in Wuhan and traveled to Anyang on January 10, 2020. She initially met with patients 2 and 3 on January 10. On January 13, she accompanied 5 relatives (patients 2 through 6) to visit another hospitalized relative in Anyang District Hospital. There was no report of COVID-19 at this hospital.

“In January 2020, we enrolled a familial cluster of 5 patients with fever and respiratory symptoms, who were admitted to the Fifth People’s Hospital of Anyang, China, and 1 asymptomatic family member,” say medical experts.

All patients underwent chest CT imaging. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) tests for COVID-19 nucleic acid were performed using nasopharyngeal swabs, describe the doctors.

The relatives -- patients 2 to 5 -- developed a fever and respiratory symptoms between January 23 and January 26 and were admitted to the hospital on the same day. All these patients had test results positive for COVID-19 within one day.

Patient 6 developed fever and sore throat on January 17 and went to the local clinic for treatment. There was no report of COVID-19 at the clinic. Her symptoms improved over the next few days but worsened on January 24, when she was admitted to the hospital and confirmed to have COVID-19 on January 26, says the report.

All symptomatic patients had “multifocal ground-glass opacities” on chest CT, and one also had “subsegmental areas of consolidation and fibrosis.” All the symptomatic patients had increased “C-reactive protein levels and reduced lymphocyte counts.”

“Patients 2 through 6 developed COVID-19. Four were women, and ages ranged from 42 to 57 years. None of the patients had visited Wuhan or been in contact with any other people who had traveled to Wuhan, except patient 1,” says the team.

After her relatives fell sick, the woman (patient 1) was isolated and put under observation. However, as of February 11, she had no elevated temperature measured or self-reported fever and no gastrointestinal or respiratory symptoms, including cough and sore throat, reported or observed by the physicians.

“Chest CT images on January 27 and 31 showed no significant abnormalities. Her C-reactive protein level and lymphocyte count were normal. Results of RT-PCR testing were negative on January 26, positive on January 28, and negative on February 5 and 8.”

According to the experts, the sequence of events suggests that the coronavirus may have been transmitted by the asymptomatic carrier. The incubation period for patient 1 was 19 days, which is long but within the reported range of 0 to 24 days, they add.