Sept. 2 (UPI) — People with confirmed COVID-19 should be retested four weeks after symptoms first appear to minimize their risk for spreading the virus, according to the authors of a study published Wednesday by BMJ Open.
In more than 1,100 infected adults in Italy, retesting four weeks later showed that 61% no longer had the virus in their systems, the research showed.
However, a second retest to confirm the initial findings showed that as many as one in five of these were “false negatives,” meaning the virus still was present.
These false negatives might have stopped self-isolating and unknowingly infected others had patients not been retested, the researchers said.
It takes an average of 30 days for the virus to clear from the body after the first positive test result and an average of 36 days after symptoms first appear, the study findings show.
“To avoid generating secondary cases, either the isolation period should be longer — 30 days from the start of symptoms — or at least one follow-up test should be done before ceasing isolation,” the researchers wrote.
It’s not yet known how infectious a person could be in the recovery phase, they said.
The World Health Organization recommends a 13-day isolation period for those with symptoms of the virus and 10 days for those without symptoms.
Earlier research has indicated that people may be contagious for as long as 37 days after COVID-19 symptoms resolve.
For this study, the team of Italian researchers tracked the progress of 4,480 residents of the Reggio Emilia province in the Emilia-Romagna region of Italy, all of whom tested positive for the virus between Feb. 26 and April 22.
By mid-April, Italy ranked third in the world for the number of cases and related deaths, and Emilia-Romagna was one of the country’s three coronavirus regional hotspots, the researchers said.
Of the 4,480 study participants, 1,259 achieved viral clearance by the end of May, as determined by at least one negative swab test after the initial positive test, and 428 died, the data showed.
The average time to viral clearance was 31 days from the first positive swab test.
The researchers then looked at the speed of viral clearance in 1,162 people out for whom at least 30 days had passed since the first positive swab by retesting them an average of three times — around 15 days after the first positive swab, 14 days after the second and nine days after the third.
Viral clearance was detected initially in 61% of the participants. However, a second test confirmed the finding in roughly 79% of them, the data showed.
The average time to viral clearance in this group was 30 days after the first positive swab and 36 days after the start of symptoms, the researchers said.
“[However], the evidence on the risk of transmission during the convalescent phase characterized by a positive [swab test] is weak, and current serological data have not provided any additional insight,” they wrote.