Covid-19 patients not infectious after 11 days: Study

Covid-19 patients no longer pose a threat of spreading the disease after 11 days, according to a new study by infectious disease experts in Singapore.

The study, which was released on May 23, was conducted jointly by Singapore’s National Centre for Infectious Diseases and the Academy of Medicine. The study examined 73 patients infected with Covid-19.

“Based on the accumulated data since the start of the Covid-19 pandemic, the infectious period of SARS-CoV-2 in symptomatic individuals may begin around two days before the onset of symptoms, and persists for about seven to 10 days after the onset of symptoms,” the study reads.

The study found that positive tests in patients that still had symptoms after two weeks could be picking up sections of the bug that cannot pass the virus on to others. These findings are supported by epidemiological, microbiological and clinical data.

According to the experts, a positive test does not equate to infectiousness or viable virus. The study says the virus could not be isolated or cultured after day 11 of illness.

It also suggests that tests can often mistakenly pick up fragments of the bug that are no longer contagious, meaning tests may still come back positive for two weeks.

“Active viral replication drops quickly after the first week, and viable virus was not found after the second week of illness,” the study read.

The study also indicates that by day 15 from onset of illness, 30 per cent of all Covid-19 patients are PCR (polymerase chain reaction) - negative by nasopharyngeal swab. This rises to 68 per cent by day 21 and 88 per cent by day 28, and by day 33, 95 per cent of all patients are negative by PCR.

PCR is a technique in molecular genetics that permits the analysis of any short sequence of DNA (or RNA) even in samples containing only tiny quantities of DNA or RNA.

The latest findings may have implications on patient discharge policy. The discharge criteria is currently based on negative test results rather than infectiousness.

“These new findings allow for revised discharge criteria based on the data on the time course of infectiousness rather than the absence of RNA detection by PCR testing, taking into consideration both the clinical and public health perspectives, like the patient’s physical and mental well-being,” the study read.