Occult SARS-CoV-2 infection; a possible hypothesis for viral relapse

Clinical and epidemiological features of patients with COVID-19 reinfection: a systematic review

Recurrent positivity in a patient with COVID-19 may be due to various reasons, not necessarily reinfection. There is concern about the occurrence frequency of reinfection. Five databases and a preprint/preprint repository were searched. All case reports, case series, and observational studies were included. Bias was assessed for each study with the Newcastle-Ottawa Scale tool and reported according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA-2020). After eligibility, 77 studies were included for qualitative synthesis (52 case reports, 21 case series, and four case-controls; 1131 patients included). Of these, 16 studies described a second contact with the SARS-CoV-2 positive case, five studies described healthcare profession-related infection, ten studies described that the source of reinfection was likely to be from the community, one study described travel-related infection, nine studies described vulnerability-related infection due to comorbidity. The mean number of days from discharge or negative test to reinfection ranged from 23.3 to 57.6 days across the different included studies. The risk of bias for all case report/series studies was moderate/high. For observational studies, the risk of bias was low. Reinfection of patients with COVID-19 occurs between the first and second month after the first infection, but beyond, and 90 days have been proposed as a point to begin to consider it. The main factor for reinfection is contact with COVID-19 positive cases.

Distinguishing repeated polymerase chain reaction positivity from re-infections in COVID-19

BACKGROUND

Possibility of reinfection with SARS-CoV-2 changes our view on herd immunity and vaccination and can impact worldwide quarantine policies. We performed real-time polymerase chain reaction (RT-PCR) follow-up studies on recovered patients to assess possible development of reinfections and re-positivity.

METHODS

During a 6-month period, 202 PCR-confirmed recovering COVID-19 patients entered this study. Follow-up RT-PCR tests and symptom assessment were performed 1 month after the initial positive results. Patients who tested negative were tested again 1 and 3 months later. The serum IgG and IgM levels were measured in the last follow-up session.

RESULTS

In the first two follow-up sessions, 82 patients continued their participation, of which four patients tested positive. In the second follow-up 44 patients participated, three of whom tested positive. None of the patients who tested positive in the first and second follow-up session were symptomatic. In the last session, 32 patients were tested and four patients were positive, three of them were mildly symptomatic and all of them were positive for IgG.

CONCLUSIONS

A positive RT-PCR in a recovering patient may represent reinfection. While we did not have the resources to prove reinfection by genetic sequencing of the infective viruses, we believe presence of mild symptoms in the three patients who tested positive over 100 days after becoming asymptomatic, can be diagnosed as reinfection. The immune response developed during the first episode of infection (e.g., IgG or T-cell mediated responses that were not measured in our study) may have abated the symptoms of the reinfection, without providing complete protection.

A systematic review on the recurrence of SARS-CoV-2 virus: frequency, risk factors, and possible explanations

BACKGROUND

Since late 2019, SARS-CoV-2 which leads to coronavirus disease 2019 (COVID-19), has caused thousands of deaths. There are some pieces of evidence that SARS-CoV-2 genome could be re-detectable in recovered patients.

METHODS

We performed a systematic review in the PubMed/Medline database to address the risk of SARS-CoV-2 recurrence. The last update was for 20 November 2020. Among the 1178 initially found articles, 66 met the inclusion criteria and were considered.

FINDINGS

In total, 1128 patients with at least one-time recurrence of SARS-CoV-2 were included. Recurrence rate has been reported between 2.3% and 21.4% in cohort studies, within a mean of 20 (ranged 1-98) days after discharge; younger patients are being affected more. Following the second course of disease, the disease severity decreased or remained unchanged in 97.3% while it increased in 2.6%. Anti-SARS-CoV-2 IgG and IgM were positive in 11-95% and 58.8-100%, respectively. Based on the literature, three possibilities include reactivation of previous disease, reinfection with the same virus, and false negative, which have been discussed in details.

CONCLUSION

There is a relatively notable risk of disease recurrence in previously recovered patients, even those who are immunised against the virus. More studies are required to clarify the underlying cause of this phenomenon.

The Effect of SARS-CoV-2 on the Spleen and T Lymphocytes

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which has infected millions of individuals in the world. However, the long-term effect of SARS-CoV-2 on the organs of recovered patients remains unclear. This study is to evaluate the impact of SARS-CoV-2 on the spleen and T lymphocytes. Seventy-six patients recovered from COVID-19, including 66 cases of moderate pneumonia and 10 cases of severe pneumonia were enrolled in the observation group. The control group consisted of 55 age-matched healthy subjects. The thickness and length of spleen were measured by using B-ultrasound and the levels of T lymphocytes were detected by flow cytometry. Results showed that the mean length of spleen in the observation group was 89.57 ± 11.49 mm, which was significantly reduced compared with that in the control group (103.82 ± 11.29 mm, p < 0.001). The mean thicknesses of spleen between observation group and control group were 29.97 ± 4.04 mm and 32.45 ± 4.49 mm, respectively, and the difference was significant (p < 0.001). However, no significant difference was observed in the size of spleen between common pneumonia and severe pneumonia (p > 0.05). In addition, the decreased count of T lymphocyte was observed in part of recovered patients. The counts of T suppressor lymphocytes in patients with severe pneumonia were significantly decreased compared with those with moderate pneumonia (p = 0.005). Therefore, these data indicate that SARS-CoV-2 infection affects the size of spleen and T lymphocytes.