Around 17% of COVID-19 Survivors Tested Positive Again During Follow-Up

In a study from Italy published in September, researchers found that, for unknown reasons, COVID-19 patients who had been hospitalized and discharged — approximately one in 6, at least 2 weeks later — had a positive PCR test again.

Sore throat and rhinitis (nasal inflammation) were the only symptoms associated with testing positive again. The study's lead author, Dr. Francesco Landi, said, "Patients who continued to have respiratory symptoms, in particular, were more likely to have a new positive test result".

Persistent Respiratory Symptoms After COVID-19 Should Not Be Underestimated

The findings of this study, which many people find surprising, show that persistent respiratory symptoms must not be underestimated and that all patients thought to have recovered from COVID-19 should be adequately assessed. Current practice worldwide assumes that people recover within 14 days of a COVID-19 diagnosis unless their condition worsens, and no end-of-illness PCR test is performed (some places test high-risk workers, such as healthcare staff).

Other reports have detected viral RNA using PCR after discharge, but this study found that only two of many symptoms — sore throat and rhinitis — were more frequent in those with a positive PCR result.

This study was published on September 18 in the American Journal of Preventive Medicine.

The findings may have important implications for people who continue to have some respiratory symptoms despite recovering from COVID-19. Dr. Francesco Landi, associate professor of internal medicine at the Catholic University of the Sacred Heart in Rome, Italy, said, "It is sensible to remain cautious after recovery, avoid close contact with others without a mask, and possibly have another nasopharyngeal swab for an additional PCR test".

Despite these findings, even if a PCR test is positive after recovery, the coronavirus RNA signal detected here does not necessarily mean that infectious virus is present. Further comprehensive viral RNA analyses are needed to answer this question.

Details of the Study Determining the Rate of Positive Tests After COVID-19

To identify clinical risk factors and the likelihood of testing positive after COVID-19, researchers evaluated 131 people after hospital discharge.

All participants met the criteria, including two negative tests at least 24 hours apart, for the World Health Organization's release from isolation and were assessed between April 21 and May 21.

• The patients' mean age was 56, and 39% were women. The average body mass index was only slightly higher in the positive group, at 27.6 kg/m2 compared with 25.9 kg/m2 in those testing negative.
• Among those discharged from hospital after COVID-19, 51% reported fatigue, 44% shortness of breath and 17% cough, but rates did not differ significantly between the groups.
• By contrast, 18% of those remaining positive after discharge and 4% of those remaining negative had sore throat; and 27% versus 12%, respectively, reported rhinitis.

People returned for follow-up visits an average of 17 days after their second negative nose-and-throat swab test.

Asymptomatic COVID-19 Carriers?

The researchers stated, "These findings suggest that a substantial proportion of patients who have recovered from COVID-19 may still be asymptomatic carriers of the virus. Even in the absence of specific guidelines for this situation, the 22 patients who tested positive for COVID-19 were advised to quarantine for a second time."

No SARS-CoV-2 infections were reported in family members or close contacts of the people who subsequently tested positive.

The researchers noted that all patients continued wearing masks and following social distancing advice, making it "very difficult to verify whether these patients were actually infectious."

Next Steps

The authors state, "Testing all COVID-19 survivors to identify those who test positive again would make a crucial contribution to better understanding both the natural history of COVID-19 and the public health implications of viral shedding".

The weakest aspect of this study is that the PCR test detects genetic sequences specific to COVID-19, but does not show whether the virus is alive or capable of replicating and causing infection.

Further studies are therefore needed to better understand whether prolonged PCR positivity for COVID-19 is actually associated with potential infectiousness.

Landi and colleagues said that their findings should be regarded as preliminary and that larger samples are needed to confirm the results.

How Protective Are Antibodies in Recovered COVID-19 Patients? On the Risk of Reinfection

The study above concerned the "risk of COVID-19 becoming chronic," but what does research say about the "risk of a second infection"?

The results were published on October 29 in NEJM; the Iceland study showed that, among 1215 people who recovered from SARS-CoV-2 infection, or COVID-19, 1107 (91.1%) developed measurable blood antibodies (IgG) against the virus, that these antibody levels continued to rise for 2 months and that elevated antibody levels lasted at least 4 months.

People who develop antibodies of the IgG type against the virus are not expected to become infected with the same virus again as long as their antibody levels remain sufficient. 

In conclusion, the Iceland study shows that antiviral antibodies against SARS-CoV-2 did not decline in 91% of patients during the 4 months after diagnosis.

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