A research letter published this week describes the case of a Chinese woman who spread COVID-19 to five people without any symptoms at all.
While international efforts are in full swing to curb the coronavirus outbreak, some view this recent finding as a cause for concern.
To date, there has been a vast majority of cases in China but the virus has now spread to 29 other countries.
Researchers have shown that the new virus, called SARS-CoV-2, is transmittable from human to human. Studies have also shown that some people may become infected with the virus but show few symptoms or no.
The recent paper, published in JAMA, is the first to describe a transmitting asymptomatic carrier of the virus to others.
Wuhan to Anyang
The paper details the observations of five individuals with respiratory symptoms and fevers admitted to Anyang’s Fifth People’s Hospital, China, and one family member without symptoms.
The asymptomatic individual is a woman, who lives in Wuhan, who is 20 years old. She traveled over 400 miles (645 kilometres) away to see the family in Anyang.
Five of her relatives exhibited SARS-CoV-2 symptoms after a few days, and she was isolated and put under observation.
Wuhan’s wife had no respiratory or gastrointestinal symptoms, and had no fever, cough, or sore throat. A CT scan showed no malfunctions.
After further testing, doctors found that her C-reactive protein levels were normal, meaning no inflammation occurred. The lymphocyte counts of the woman were also normal, suggesting no immune response.
However, reverse transcriptase polymerase chain reaction testing in real time confirmed she had been infected with SARS-CoV-2.
COVID-19 was developed by all five members of her family-four women and one man. None had ever visited Wuhan or had any other contact with anyone who had visited Wuhan.
What does this mean?
The researchers are confident that this case study describes an asymptomatic carrier that transmits the infection to others, but as it is the first report, one has to be careful when drawing conclusions.
The authors, in general, are concerned about the possibility, writing:
“If the findings in this report of presumed transmission by an asymptomatic carrier are replicated, the prevention of COVID-19 infection would prove challenging.”
A letter dated January 30 published in The The New England Journal of Medicine described a similar case. It reported that a woman from Shanghai who had no symptoms had passed the infection to a German man.
The writers of the letter wrote that “The fact that asymptomatic persons are potential sources of[ SARS-CoV-2] infection may warrant a reassessment of the current outbreak’s transmission dynamics.”
However, it turned out that the woman had, in fact, experienced mild symptoms, including that of the current outbreak. Before the material was published the authors had not managed to speak directly with the woman.
Information about this outbreak is being published thickly and quickly; during an epidemic, all are focused on getting data into the public domain.
In an interview with Science, Prof. Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health in Boston, MA, explains how these situations can change the way in which scientific evidence is compiled and disclosed:
“I think peer review is lighter in the midst of an epidemic than it is at normal speed, and the quality of the data that goes into the papers is necessarily greater.
Overall, the current case study is convincing but it needs more analysis.
It should also be remembered that asymptomatic carriers do not sneeze or cough, which are some of the main ways the virus spreads. Because of this, it’s unclear how much of a role these individuals will play in SARS-CoV-2 transmission.