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A young woman from Wuhan, China visited five family members, who all contracted novel coronavirus, COVID-19, in the first-ever documented case of an asymptomatic carrier with normal chest CT imaging results, researchers found.

The woman, age 20, was afebrile and had no respiratory symptoms, including cough and sore throat, no gastrointestinal symptoms, no significant abnormalities on chest CT imaging, and no laboratory abnormalities.

Yet, she tested positive for the novel coronavirus, reported Meiyun Wang, MD, PhD, of Henan Provincial People's Hospital in Henan, China, and colleagues.

More concerning may be that the incubation period for the woman was documented as 19 days, outside of the long-held belief about a 14-day incubation period, the authors wrote in a research letter in .

In fact, they sounded a note of warning if what they discovered in this case turns out to be true elsewhere:

"The sequence of events suggests that the coronavirus may have been transmitted by the asymptomatic carrier ... 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 team wrote.

While this research was not specifically referenced, a reporter asked Nancy Messonnier, MD, director of CDC's National Center for Immunization and Respiratory Diseases in Atlanta, about asymptomatic transmission on a press call with reporters on Friday.

"We need to fully understand what [asymptomatic] means in those individual patients. Are patients being caught early, who then go on to get disease? How hard are [clinicians] looking for symptoms?" she said, noting that in similar illnesses, a patient can recall "mild symptoms" following a deeper dive into their history.

That appeared to be the case with the first report of asymptomatic transmission when a woman from China visited Germany back in January and several of her colleagues contracted the illness, although additional information revealed vague symptoms when the patient was asked later.

Wang and colleagues noted that asymptomatic carriers had been demonstrated, citing the case of an infected boy, , but not asymptomatic transmission with normal imaging.

In this case, the woman left Wuhan, China on Jan. 10 and accompanied five relatives to visit another hospitalized relative in Anyang, China, where there was no report of COVID-19 at the time. These five relatives ranged in age from 42 to 57, four were women, and none had been in contact with anyone who visited Wuhan except the index patient. All developed COVID-19 infection.

From Jan. 23 to Jan. 26, four of the patients developed fever and respiratory symptoms and were admitted to the hospital. The fifth developed fever and sore throat on Jan. 17, and was ultimately admitted to the hospital on Jan. 24. Three had moderate infection, and two developed severe pneumonia.

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

However, as of Feb. 11, the presumed asymptomatic carrier had no fever, no symptoms, and no lab abnormalities, including C-reactive protein level and lymphocyte count. She tested negative on Jan. 26, before testing positive on Jan. 28, and negative on Feb. 5 and 8. Chest CT images taken on Jan. 27 and 31 showed no abnormalities, the authors said.

They also disputed the idea that the second reverse transcription polymerase chain reaction result could have been a false positive, as the test has been "widely deployed" and yielded "few false-positive outcomes." But they acknowledged that asymptomatic carriers in general require further study.

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