Coronavirus patients are not infectious after 11 days of illness even if they test positive: Study
Coronavirus patients are no longer infectious after 11 days of getting sick, even though some may still test positive, according to researchers. A positive test "does not equate to infectiousness or viable virus", says a joint paper by the National Centre for Infectious Diseases (NCID) and the Chapter of Infectious Disease Physicians, Academy of Medicine, Singapore. The findings could have implications for countries that are trying to figure out how to safely reopen their economies.
"Countries that have adopted a policy of repeating respiratory sample PCRs (polymerase chain reaction) to determine negativity (for example two negative PCRs 24 hours apart) to guide discharge and de-isolation policies (China, Korea) have reported that some patients have recurrent positive PCRs after initial negatives. This has led to some speculation of a ‘persistent carrier state’ or ‘recurrent infections’ but these have not been substantiated, to date," researchers say in the study.
Accordingly, the research team studied 73 coronavirus patients to understand the infectiousness of people with Covid-19. The analysis shows that an infected person becomes contagious around two days before symptoms show, and they remain contagious for between seven and 10 days after they start showing signs of the disease. The researchers also found that after day 11 of the illness, the virus could not be isolated or cultured. The findings indicate that infectiousness begins just before and with the onset of symptoms and rapidly declines by the end of the first week of disease. The experts say the results are in keeping with available evidence that indicates that SARS-CoV-2 seems to have a consistent trajectory, and while viral RNA may be detectable for about two to four weeks from the onset of disease, the infectiousness diminishes after seven to 10 days.
"Based on the accumulated data since the start of the Covid-19 pandemic, the infectious period of SARS-CoV-2 (the virus that causes Covid-19) in symptomatic individuals may begin around two days before the onset of symptoms, and persists for about 7-10 days after the onset of symptoms. Active viral replication drops quickly after the first week and viable virus was not found after the second week of illness despite the persistence of PCR detection of RNA," the findings state.
According to the researchers, robust data are lacking regarding the infectiousness of asymptomatic and presymptomatic individuals and how much asymptomatic infection drives the transmission. However, asymptomatic people may have similar viral shedding patterns, say experts. "A Singapore study found pre-symptomatic transmission of SARS-CoV-2 in about 6.4% of 157 locally acquired cases, but no asymptomatic transmission," they add.
The team says that their findings allow for revised discharge criteria based on the data on the time course of infectiousness rather than the absence of RNA detection by testing, taking into consideration both the clinical and public health perspectives, including the individual patient’s physical and mental well being. In addition, given these findings, "resources can focus on testing persons with acute respiratory symptoms and suspected Covid-19 in early presentation", allowing timelier public health intervention and containment, say researchers.
A previous study from South Korea had also concluded that people who test positive despite having recovered from Covid-19 are neither reinfected nor contagious. According to scientists, the finding indicates that the diagnostic tests could be picking up on the genetic material from non-infectious or dead viruses. A second positive test after a negative result may mean the virus is simply taking its time leaving the body and is no longer able to infect others, said experts.