A novel coronavirus has caused a viral pneumonia outbreak in China. There is evidence of person-to-person transmission. But, the researchers have not yet seen reports of COVID-19 transmission from an asymptomatic carrier. The carrier would have a normal chest computed tomography (CT).
The researchers report a possible transmission of COVID-19 through an asymptomatic carrier.
In January 2020, the physicians admitted 5 symptomatic and 1 asymptomatic family members. The symptomatic patients had fevers and respiratory symptoms. The physicians analyzed patient records. All patients received chest CT scans. Physicians used nasopharyngeal swabs and real-time reverse transcriptase polymerase chain reaction (RT-PCR) tests to test for COVID-19.
Let's assume the asymptomatic carrier is patient 1. Patient 1 is a 20-year old woman from Wuhan. She traveled to Anyang on January 10, 2020 to meet patients 2 and 3. On January 13, she went with patients 2 to 6 to visit a relative in another hospital (Figure). This hospital had no reported cases of COVID-19. When the five relatives developed symptoms, physicians isolated patient 1. Patient 1 had no symptoms as of February 11. She had no fever, gastrointestinal, nor respiratory symptoms. Chest CTs on January 27 and 31 had no abnormalities. The table shows she had normal C-reactive protein levels and lymphocyte counts. She tested negative on January 26, positive on January 28, and negative on February 5 and 8.
Patients 2 through 6 developed COVID-19. Four were women, and ages ranged from 42 to 57 years. None of them had traveled to Wuhan or was in contact with anyone from Wuhan except for patient 1. Patients 2 to 5 developed fevers and respiratory symptoms between January 23 and 26. All patients had positive RT-PCR results within 1 day. Patient 6 developed a fever and sore throat on January 17. She went to a local clinic for treatment. There were no reported cases in the clinic. Her symptoms worsened, so she went to the hospital, where she tested positive on January 26. Two patients developed severe pneumonia. The rest of the infections were moderate.
The symptomatic patients had CTs that showed multifocal ground-glass opacities. One also had subsegmental areas of consolidation and fibrosis. All symptomatic patients had increased C-reactive protein levels and reduced lymphocyte counts (Table).
The familial cluster of COVID-19 in Anyang, China had contact with the asymptomatic family member. The timeline of events suggest that the asymptomatic carrier transmitted the coronavirus. The patient had an incubation period of 1 to 19 days, which is long. But, this is within the reported range of 0 to 24 days. Her first PCR test was negative. False negatives are due to the quality of the kit, the quality of the sample, or performance of the test. RT-PCR is often used for viral diagnoses. It has very few false positives. Thus, the positive result was unlikely to be a false positive. The physicians counted this test as the date patient 1 had a confirmed infection.
Another study showed a 10-year old boy was asymptomatic. But, he had an abnormal chest CT. If researchers replicate these findings of asymptomatic transmission, the coronavirus infection will be difficult to prevent. The mechanism in which asymptomatic carriers acquire and transmit the virus needs more research.