People with Covid-19 may be infectious days before symptoms: study

PARIS: People infected with the new coronavirus may start spreading the virus several days before they have any noticeable symptoms, according to a new modelling study published Wednesday. The study comes as nations have broadened restrictions aimed at curbing the epidemic, amid concerns over patients who may be infectious despite not showing signs of ill health. The findings challenge key assumptions behind measures put in place to stop the spread of the pandemic, such as tracing contacts of an infected person only as far back as the time at which they began to show symptoms. Experts have long conjectured that some people who do not even know they are infected may transmit the virus. But the new study suggests that even those who get visibly sick may be highly infectious before the onset of symptoms. “More inclusive criteria for contact tracing to capture potential transmission events two to three days before symptom onset should be urgently considered for effective control of the outbreak,” the authors said in the paper published in Nature Medicine.

INFECTIOUS BEFORE SYMPTOMS SHOW: Researchers compared clinical data on virus shedding from patients at a hospital in China with separate data on “transmission pairs” — where one person is believed to have infected the other — to draw inferences about periods of infectiousness. The research team co-led by Eric Lau of the University of Hong Kong took throat swabs from 94 patients admitted to Guangzhou Eighth People´s Hospital and measured infectiousness from the first day of symptoms for 32 days. They found that the patients, none of whom were classed as severe or critical, had the highest viral load soon after the onset of symptoms, which then gradually decreased.