A new research paper from China published on the preprint server medRxiv* claims that recurrent positive results for SARS-CoV-2 are due to the presence of low levels of viral RNA fragments and not the shedding of infectious virus particles.
Recurrent Positives: The Risk
The ongoing COVID-19 pandemic has spread all over the world, causing over 659,000 deaths and an astonishing 16.67 million-plus confirmed cases. Of these, approximately 6.5 million are currently infected, and almost 10 million have recovered.
Almost from the beginning, reports have cropped up of patients who apparently recovered and were discharged testing positive on reverse transcriptase-polymerase chain reaction (RT PCR) testing for the viral RNA. These are called recurrent positives. In most cases, these reports dealt with small numbers of patients, who were typically asymptomatic or had only mild symptoms.
The concern with recurrent positives (who have repeatedly tested negative before this result) is that they might be silent carriers of the virus, driving community transmission. In response, the Chinese government places such patients in quarantine for 14 days, a complicated and expensive effort.
The Study: Recurrent Positives
The current study is aimed at filling in the knowledge gap concerning these patients, their viral RNA level, the antibody responses, and the risk of viral spread. This will, it is hoped, help evolve more suitable management methods.
The paper is based on an observational study of 479 recovered COVID-19 patients who were discharged between February 1, 2020, and May 5, 2020. All these patients had been discharged following a normal temperature recording for 3 or more days, the resolution of all airway symptoms, and a significant decrease of pulmonary lesions on chest computed tomography (CT), as well as two negative successive RT PCR tests, carried out at an interval of one day.
Discharged patients were quarantined at home or in quarantine facilities for two weeks, with repeated RT PCR tests of nasopharyngeal and rectal swabs, on the 7th and 14th days, up to March 18, or on day 1, 3, 7 and 14 after that date. On the latter days, serologic testing was performed. Specimens were taken from 147 discharged patients with recurrent positives for RNA detection by RT PCR, at 1-4 samples per person.
Of the 479 patients, there were 93 (19%) recurrent positives, with 9% who had multiple positive tests after two consecutive negatives and discharge. Of the 93, 75% tested positive during the 14-day quarantine, and the rest during their follow up. The median period from discharge to the first recurrent positive test was 8 days. Still, the final recurrent positive test occurred at a median of 15 days from discharge, and 46 days from disease onset.
In this small cohort, about 60% were female, and significantly younger, at 34 years, compared to the median age of 45 years for the rest of the patients. Both recurrent and non-recurrent positive patients had similar characteristics as far as the severity of the disease, steroid use, or period of hospitalization. However, the former had markedly higher C-reactive protein levels at first presentation but not at discharge.
Among the recurrent positives, those with multiple positive tests had more prolonged periods of hospitalization, at 24 vs. 18 days for single recurrent positive patients, and double the period of detection of viral RNA at 65 days vs. 33 days.
Symptoms were absent in 72% of recurrent positive patients, while the rest had mild symptoms only. Only one patient had a single sign of inflammation in the form of a high IL-6 level. In 80% of patients, the lung lesions had improved (73%) or remained unchanged from the first discharge (8%).
In about three of four patients, only the nasopharyngeal swabs were positive, in 15% only rectal swabs, and in less than a tenth, both were positive. All blood tests proved negative for viral RNA. The viral RNA titers were much lower than at the onset of disease, at below 5 log copies/ml in over 95% of patients. This was a consistent finding across single and multiple recurrent positive patients. Moreover, the titer went down with an increasing number of days from discharge.
Almost every recurrent positive patient was IgG positive, with 62% being IgA positive and 88% positive for neutralizing antibody. These values were comparable to those of non-recurrent positive patients. The titer of neutralizing antibodies was 1:32 and 1:16, respectively.
Virus isolation was unsuccessful from 9 selected recurrent positive nasopharyngeal swabs, while whole genome sequencing methods retrieved only fragments of the genome.
Do Recurrent Positives Spread the Infection?
The patients identified as recurrent positives were analyzed for viral transmission to 96 close contacts. Follow up for two weeks revealed that none were symptomatic, with all having negative PCR results. Anti-RBD antibodies were not found in 20 tested samples from these contacts.
One notable recurrent positive was a student who attended school for 11 days before testing positive 90 days from discharge. All of the 1,200 teachers and classmates who came in contact with him had negative tests for viral RNA and did not have any symptoms. Overall, no evidence was found of even one new case related to these recurrent positives.
All the recurrent positive patients were tested until their viral RNA detection tests became positive. None of them returned further recurrent positive tests after this second discharge. The vast majority of them had neutralizing antibodies with a median titer of 1:32.
Characteristics of Recurrent Positives
The common characteristics of recurrent positive patients, based on this study, include younger age, mild or absent symptoms, nonprogressive disease, low viral RNA titers, and long periods of positive testing for the viral RNA for up to 113 days. The lack of significant differences in antibody titers or neutralizing antibody levels indicates that humoral immunity development is similar in both classes of patients. Finally, the risk of viral transmission is low among these recurrent positive patients. With a neutralizing antibody titer of 1:32 or more in 60% of patients who fully recovered, this could be a possible benchmark for future vaccine trials.
What Causes Recurrent Positive Tests?
The reasons for recurrent positivity are not clear but may include false-negative RT PCR tests leading to discharge, true recurrent infection after discharge, and persistence of the virus due to weakened immunity. However, the present study does not support any of these hypotheses. The researchers consider that dead virus particles are possibly being shed, leading to the lack of live particles along with repeat positives for the viral RNA test.
They point out that more sensitive methods of live virus detection are needed to rule out this theory since, at present, prior studies show that it is not possible to isolate live virus when the viral load is less than 106 copies per ml. They propose that “intermittent and non-stable excretion of low levels of viral RNA” is likely to be the cause for recurrent positive testing.
Implications and Future Directions
The study concludes: “Our study found that intermittent detection of low levels of SARS-CoV-2 RNA [in discharged patients] is not rare and that the timing of RP detection varies (up to 90 days post-discharge). The transmission risk posed by RP-DC patients is likely low.” The researchers recommend a relaxed approach to managing discharged patients, given this, to minimize the economic and psychological cost of more extended quarantine periods, while maintaining proper personal protection and follow up.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.