key: cord-0988382-tref7dq9
authors: Olea, Beatriz; Albert, Eliseo; Torres, Ignacio; Gozalvo-Rovira, Roberto; Carbonell, Nieves; Ferreres, José; Poujois, Sandrine; Costa, Rosa; Colomina, Javier; Rodríguez, Jesús; Blasco, María Luisa; Navarro, David
title: Lower respiratory tract and plasma SARS-CoV-2 RNA load in critically ill adult COVID-19 patients: relationship with biomarkers of disease severity
date: 2021-06-01
journal: J Infect
DOI: 10.1016/j.jinf.2021.05.036
sha: 9c5ab1c08d50dd8ea95c94744654d11dc549d63c
doc_id: 988382
cord_uid: tref7dq9

nan

We read with interest the work published by Lui and colleagues in the Journal of Infection [1] , in which the dynamics of SARS-CoV-2 RNA at different body sites was investigated in a rather small cohort including 5 patients with critical/severe COVID-19.

The authors supported the assumption that viral loads in lower respiratory tract (LRT) better reflected clinical progression in severe disease than those in upper respiratory tract (URT) samples. To further address this issue, we conducted an observational study ( Table 1 ). Patients were admitted to ICU at a median of 9 days (range, 2-25) after onset of symptoms. Sixty-four patients underwent mechanical ventilation, from whom 165 tracheal aspirates (TA) were collected (median of 2 specimens/patient; range, 1-11). A total of 340 plasma specimens (median, 4 samples/patient; range, 1-16) were available from the 73 patients. SARS-CoV-2 RNA quantitation in TA and plasma was carried out by the Abbott RealTime SARS-CoV-2 assay Abbott Molecular (Des Plaines, IL, USA) (See Supplementary Material). SARS-CoV-2 viral loads (in copies/ml) were estimated using the AMPLIRUN® TOTAL SARS-CoV-2 RNA Control (Vircell SA, Granada, Spain). The analytical sensitivity of the RT-PCR assay in TA and plasma specimens was 100 copies/ml (95%) for both matrices.

SARS-CoV-2 RNA (median, 6.5 log 10 copies/ml; range, 3.03-10.6 log 10 ) was detected in 109 TA from 56 patients (91.8%). Viral load remained relatively stable across the first two weeks from symptoms onset and began to decrease afterwards (Fig. 1A) . No patient tested positive for SARS-CoV-2 RNA in TA beyond day 42. As reported for URT [2, 3] , neither remdesivir nor tocilizumab administration appeared to have a major impact on the dynamics of SARS-CoV-2 RNA load in TA (Supplementary Table 2 ). SARS-CoV-2 RNAemia (median, 3.03 log 10 copies/ml; range, 1.69 to 5.27 log 10 ) was detected in 37 plasma specimens from 26 patients (35.6%). Median time to first detection of viral RNA in plasma was 10 days after symptoms onset (range, 3-32 days) Viral RNA cleared faster in plasma than in TA (Fig. 1B) . Previous studies using a droplet-based digital PCR, which seemingly outperforms conventional RT-PCR assays in terms of sensitivity, reported higher rates of viral RNAemia detection in ICU patients (77% in [4] and 88% in [5] ) than found in the current study. This discrepancy could also be related to different timing of sample collection across studies.

A moderate yet significant correlation was found between SARS-CoV-2 RNA levels in TA and in paired plasma specimens (rho, 0.41; P<0.001). SARS-CoV-2 RNA load in TA was significantly higher (P<0.001) in presence than absence of concomitant viral RNAemia (median, 9.5 log 10 copies/ml; range, 4.3 to 10.4 log 10 copies/ml vs. median, 6.2 log 10 copies/ml; range, 3.0-10.6 log 10 copies/ml), this suggesting that LRT may be a substantial source of SARS-CoV-2 RNA.

Plasma levels of ferritin, lactose dehydrogenase (LDH), but not interleukin-6 (IL-6), Creactive protein (CRP), or D-Dimer (D-D), were significantly higher when SARS-CoV-2 RNA was detected in paired TA or plasma specimens (Table 1 ), yet SARS-CoV-2 RNA loads in these specimens correlated modestly (Rho<0.31) with plasma levels of ferritin and LDH (Supplementary Fig 1) . Lymphocyte counts were significantly lower in the presence of SARS-CoV-2 RNA in TA and plasma (Table 1) . Nevertheless, the level of correlation (inverse) between SARS-CoV-2 RNA load in TA and plasma and lymphocyte counts was modest ((rho, -0.43; P<0.01 and rho, -0.25, P<0.01, respectively). A significant association between SARS-CoV-2 RNAemia detection and blood levels of IL-6, interleukin-10, CRP, ferritin, D-D and LDH was previously reported [4, 6] . In these studies, a single time point specimen per patient collected at ICU admission was considered for the analyses, as opposed to the serial specimens used herein.

Dynamics of SARS-CoV-2 RNA load (initial, peak and trajectory) in TA following ICU admission were comparable across patients who either died or survived ( Figure 1C ). Moreover, neither initial nor peak viral load in TA was associated with increased mortality (OR, 0.81; 95% CI, 0.68-2.24; P=0.68, and OR, 0.39; 95% CI, 0.22-1.82; Table 3 ). Other studies, in contrast, pointed to an association between protracted SARS-CoV-2 RNA clearance in LRT and/or simple presence of SARS-CoV-2 RNA in LRT and increased risk of mortality [7] [8] [9] . In these studies, a wide variety of LRT specimens were used, and no data proving a dosedependent relationship between SARS-CoV-2 RNA load in LRT and mortality were provided.

We found a trend towards an association between qualitative detection of SARS-CoV-2 RNA in plasma and increased mortality in adjusted multivariate logistic regression models (OR, 2.82, 95% CI, 0.94-8.47), and failed to demonstrate such a trend for initial or peak viral loads (supplementary Table 3 ). SARS-CoV-2 RNAemia has been previously associated with poor clinical outcome in series including only ICU patients, in which patients who died displayed higher viral RNA loads in plasma collected at ICU admission than those who survived [4] .

The main limitation of the current study is its relatively small sample size. Analysis of sequential specimens from patients could be considered a strength of the research.

The current study provides a further insight into the pathogenesis of SARS-CoV-2 infection in ICU patients. In our view, our data fit better with a pathogenetic model, in which SARS-CoV-2 replication in the LRT or its presence in blood at a certain point over the course of ICU stay might not be a major driver of systemic inflammation, lymphopenia, lung dysfunction, multisystemic organ failure and death. This does not invalidate the importance of virus replication rate in the URT in the early stage after infection in determining the clinical course of COVID-19 [10] . Further studies are needed to resolve this issue.

No public or private funds were used for the current study. We are grateful to all personnel who work at Clinic University Hospital, in particular to those at Microbiology laboratory and the Intensive Care Unit for their commitment in the fight against COVID-19. Eliseo Albert holds a Juan Rodés Contract (JR20/00011) from the Health Institute Carlos III. Ignacio Torres holds a Río Hortega Contract (CM20/00090) the Health Institute Carlos III.

This work received no public or private funds.

The authors declare no conflicts of interest. 

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