Study of the outbreak in Italy suggests Covid-19 recoveries should be retested about a month later

  • More infected patients would be pronounced clear of the coronavirus if tested a month after symptoms appear 
  • This will help reduce testing costs and overloading the system, according to a study
  • They also found that people should be also be isolating themselves for longer after symptoms disappear

You got infected with Covid-19, recovered and now want to return to your daily life. But a new study on Italian survivors indicate that you might still be carrying the virus around a month after you started exhibiting symptoms.

Published in BMJ Open, the research focused on how long viral shedding of SARS-CoV-2 goes on for, based on population data. This is important to understand as healthcare workers could be swamped with retesting to clear an infected patient.

They also wanted to determine the probability of viral clearance confirmation with two negative swabs, and what factors might possibly influence their outcomes.

READ | Retroactive Covid-19 testing indicates numbers in Wuhan and Seattle initially far higher 

Italian patients

They assessed the follow-ups of 1 162 patients in the Regio Emilia province in northern Italy, one of the hardest-hit regions during their outbreak a month after diagnosis and symptom onset to see how many patients were still carrying the viral load of the virus, and how many had been completely cleared.

From that group, 172 people died, most having been hospitalised with an average age of almost 80 years. 

"During follow-up, each patient underwent an average of three swabs, with a range of from one to nine. The mean time of retesting after positive swabs was 14.7 days after the first positive, 14.0 days after the second positive, and 9.2 days after the third positive swab," explain the researchers.


Their study showed that 60.6% of patients was cleared of the coronavirus viral load at an average of 30 days from diagnosis, and 36 days from symptom onset. They also found that one in five tests was a false negative in their cohort.

Age also played a factor. Viral clearance from symptom onset was on average 35 days for those under 50, and 38 days for those over the age of 80. A similar pattern was also noticed when it came to disease severity – those who were hospitalised took longer to clear the virus.

"The probability of confirmed viral clearance reached 86.8% after 34 days from symptom onset and increased with time, even when adjusting for age and sex."

The researchers concluded that this might mean that testing should be postponed after a patient recovers to ensure efficiency and increase testing performance.

READ MORE | Testing for Covid-19? All you need to know about antibody tests 

Key considerations

It is, however, important to note that viral clearance was only confirmed at the time of the swab, and could have happened much earlier after the previous swab, which means the more time between tests, the more likely that the time to clearance will be overestimated. 

The tests are also designed to pick up even the tiniest fragment of the virus, meaning you might test positive even if you're no longer infectious. 

"The half-life of up to three months of respiratory epithelial cells and the detectability of genetic materials from a live virus, or even from fragments of dead virus by [testing] should also be considered in order to understand the inconsistency in negative results over a prolonged period."


However, this study reflects real-world data and practice in terms of delayed testing due to overloaded healthcare systems, strengthening its recommendations. 

"Our data indicate that testing at 14 days from diagnosis, as many regional surveillance protocols recommend, will result in most cases still being positive.

"So that at least half of these tests are negative, testing should be done after more than four weeks once patients are symptom-free. What’s more, given the high probability a priori of viral persistence, negative tests three weeks from diagnosis have a high probability of being false negatives."

They also don't believe indicators like sex, age and disease severity should be used to test earlier or later, as this is insignificant. 

Another implication for their results is recommended isolation for those who have tested positive for Covid-19. If clearance is only achieved after 30 days – and even longer – it might mean that people should be isolating themselves for longer than common policies dictate after symptoms have cleared.

"To avoid generating secondary cases, either the isolation period should be longer (over 30 days from symptom onset), or at least one follow-up test should be done before ceasing isolation."

WATCH | Why are scientists testing a TB vaccine to see if it protects against Covid-19?

Image credit: Yu

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