Study suggests a time frame for COVID-19 retest

There has been a lot of speculation about the timing for the second swab test for patients infected with the new coronavirus. While the time frame varies from country to country, a new study suggests that the patient should be retested after four weeks to minimize the risk of spreading the virus. 

From the first positive test date, it would take an average of 30 days for the SARS-CoV-2, the virus that causes the COVID-19 infection to get flushed out from the patient, according to a peer-reviewed study published in the online journal BMJ Open on Thursday. 

If the time is calculated from the day when the symptom of the infection started showing, then patients must wait for around 36 days to get a second swab test.

"It's not yet known how infectious a person may be in the recovery phase," researchers warned.

According to previous studies, a coronavirus patient may not be infectious after recovering from the infection, even if they test positive. The findings prompted the World Health Organization (WHO) to recommend isolation for 13 days for patients with symptoms and 10 days for those showing no signs of the infection.

"An accurate assessment of how long it takes the body to clear SARS-CoV-2 is key to curbing the risk of onward infection and minimizing the enforced isolation period for patients who no longer have symptoms," said the researchers. 

In order to calculate the time frame for the coronavirus retest, researchers studied 4,538 COVID-19 patients at the Reggio Emilia province in the Emilia-Romagna region of Italy, which was one of the three coronavirus hotspots in the country.

The average time to viral clearance was 31 days of the first positive swab test, the study found. Around 1,160 patients were selected to further study the speed of viral shedding, with each of them retested thrice after the first positive test. 

"Retesting 14 days after a positive swab will, in most cases, produce the same result, and that there's still a relatively high rate of false-negative results when retesting up to three weeks later," said the study.

(A migrant worker undergoes a COVID-19 swab test at a dormitory in Singapore, April 28, 2020. /Reuters)