COVID-19 lung alterations still evident at 60-day follow-up chest CT in asymptomatic patients despite negative rRT-PCR testing

Several patients who have recovered from COVID-19 pneumonia showed persistent infection at follow-up chest CT (31-63 days after disease onset) despite being asymptomatic and testing negative at rRT-PCR. based on chain and include The purpose of this report is to compare the findings of chest CT with the rRT-PCR results in the follow-up of patients discharged after hospitalization for COVID-19 pneumonia. (d), of and (1%), residual (f).


Introduction
Italy was the first European country to confront the COVID-19 pandemic outbreak. Despite a high death toll, it is now observing the aftermath of the disease.
The Centers for Disease Control have issued return-to-work criteria based on real-time reverse transcriptionpolymerase chain reaction (rRT-PCR) and symptoms improvement [1], which, however, do not include imaging findings.
The purpose of this report is to compare the findings of chest CT with the rRT-PCR results in the follow-up of patients discharged after hospitalization for COVID-19 pneumonia.

Patient Population
The Institutional Review Board of (*BLINDED*) approved this retrospective study; informed consent was acquired before every CT. Medical records of all consecutive patients admitted for COVID-19 pneumonia from January to April 2020 in (*BLINDED*) were reviewed. Inclusion criteria were: a) hospitalization for SARS-CoV-2 confirmed by positive rRT-PCR b) non-contrast chest CT at admission c) hospital discharge with full clinical recovery d) followup chest CT performed at least 30 days after initial symptoms onset.

Chest CT visual and quantitative analysis
Chest CTs were acquired without contrast administration on a 64-row scanner and reformatted with 2 mm slice thickness. A single reader (*BLINDED*) visually evaluated all the exams and assessed the presence of features attributable to residual COVID-19 pneumonia.

Statistical analysis
Logistic regression tests were performed to find the best lung volume to monitor COVID-19 pneumonia at followup. The dependent variable was the visual evidence of residual disease. Statistical significance was set at p<.05.

Results
From January 25th to April 21st, 2020, 401 patients hospitalized for COVID-19 underwent a CT scan at admission. Thirty-six patients who had a follow-up chest CT from April 11th to 24th were included in the study.

Discussion
Our study suggests that several patients with COVID-19 discharged after hospitalization still present an active infection at follow-up CT, despite being asymptomatic and having tested negative at rRT-PCR in the majority of cases. These results are in keeping with a similar report for chest X-Ray [4] and highlight the lack of an evidencebased algorithm for declaring a patient as disease-free.
Asymptomatic transmission is considered the Achilles' Heel of the current global strategy to control COVID-19 [5], and there is no available evidence that patients with positive CT findings are not capable of transmitting the infection. The premature reinstatement in the community of an individual with active disease may prevent the pandemic curve from decreasing.
Although preliminary and from a single center, our results may warn the medical community that 1) COVID-19 disease span is wide and may exceed 60 days 2) rRT-PCR alone seems inadequate to declare a patient as disease-free 3) chest CT may be the ideal tool not only for early diagnosis but also for disease monitoring and infection-control strategies, especially with the added value of quantitative analysis.

Declarations
Our study has been approved by the Institutional Review Board of Humanitas Clinical and Research Hospital (Rozzano, Milan).

Figure 1
Chest CT of a 75-year-old man admitted for COVID-19 pneumonia. a) Bilateral peripheral ground-glass opacities and consolidation, predominantly in the left lung b) Quantitative analysis highlights in blue the ground-glass volume (%GGO), in yellow the poorly aerated (%PAL) and in green the non-aerated (%NAL) c) Pie chart