A new SARS-CoV-2 variant poorly detected by RT-PCR on nasopharyngeal samples, with high lethality
Authors: Fillatre Pierre , Dufour Marie-José , Behillil Sylvie , Vatan Remi , Reusse Pascale , Gabellec Alice , Velmans Nicolas , Montagne Catherine , Geffroy Sophie , Droumaguet Edith , Merour Véronique , Enouf Vincent , Buzele Rodolphe , Valence Marion , Guillotel Elena , Gagniere Bertrand , Baidaluk Artem , Zhukova Anna , Tourdjman Mathieu , Thibault Vincent , Grolhier Claire , Pronier Charlotte , Lescure Xavier , Simon-Loriere Etienne , Costagliola Dominique , Van Der Werf Sylvie , Tattevin Pierre , Massart Nicolas 
Published: May 2021

Background

In early January 2021, an outbreak of nosocomial cases of COVID-19 emerged in Western France, with RT-PCR tests repeatedly negative on nasopharyngeal samples but positive on lower respiratory tract samples. Whole genome sequencing (WGS) revealed a new variant, currently defining a novel SARS-CoV-2 lineage: B.1.616. In March, WHO classified this variant as ‘under investigation’ (VUI). We analyzed the characteristics and outcomes of COVID-19 cases related to this new variant.

Methods

Clinical, virological, and radiological data were retrospectively collected from medical charts in the two hospitals involved. We enrolled patients with at least one of the following: i) positive SARS-CoV-2 RT-PCR on a respiratory sample; ii) seroconversion with anti-SARS-CoV-2 IgG/IgM; iii) suggestive symptoms and typical features of COVID-19 on chest CT scan. Cases were categorized as either: i) B.1.616; ii) variant of concern (VOC); iii) unknown.

Findings

From January 1st to March 24th, 2021, 114 patients fulfilled the inclusion criteria: B.1.616 (n=34), VOC (n=32), and unknown (n=48). B.1.616-related cases were older than VOC-related cases (81 years [73-88], vs 73 years [67-82], P<0.05) and their first RT-PCR tests were less often positive (5/34, 15% vs 31/32, 97%, P<0.05). The B.1.616 variant was independently associated with severe disease (multivariable Cox model HR 4.2 [1.3– 13.5], P=0.018), and increased lethality (logrank test P=0.01): 28-day mortality 15/34 (44%) with B.1.616, vs. 5/32 (16%) for VOC, P=0.036.

Interpretation

We report a nosocomial outbreak of COVID-19 cases related to a new variant, B.1.616, poorly detected by RT-PCR on nasopharyngeal samples, with high lethality.

Research in context

Evidence before this study

Among the numerous SARS-CoV-2 variants described worldwide, only 3 are currently classified as Variant of Concern (VOC) by the WHO, since they are associated with either an increased risk in transmissibility, severity, or significant reduction in neutralization by antibodies: B.1.1.7, B.1.351 and P.1 (Pango lineage nomenclature). With the ongoing circulation of SARS-CoV-2 in many places worldwide, the emergence of new variants may reduce the efficacy of vaccines and jeopardize our prospects to control the pandemic. In early January 2021, an outbreak of cases highly suggestive of COVID-19 despite negative RT-PCR tests on repeated nasopharyngeal (NP) samples was reported in Western France, leading to several nosocomial clusters. Whole-genome sequencing (WGS) from lower respiratory tract samples identified a new lineage of SARS-CoV-2 virus, classified as B1.616. Consequently, the French public health agency (Santé publique France) and the WHO classified B.1.616 as ‘variant under investigation’ (VUI).

Added value of this study

Our observational study, conducted from January 1st to March 24th 2021 in the B.1.616 identified area, provides the first clinical and virological description of B.1.616-associated COVID-19. The 34 cases had clinical, biological and radiological findings in line with classical features of COVID-19, while RT-PCR tests on nasopharyngeal (NP) samples failed to detect SARS-CoV-2 in most patients. Indeed, this gold-standard test was positive in only 15% of the first tests in B.1.616-related COVID-19 patients. Of note, the diagnostic performance of RT-PCR tests was satisfactory on lower respiratory tract samples, suggesting that failure to detect B.1.616 on NP samples would be due to a viral load below the limit of detection in the upper respiratory tract, rather than to genomic mismatches between routine RT-PCR targets and this variant. In our cohort, B.1.616 was independently associated with worse clinical outcome, with high 28-day mortality (44%).

Implications of all the available evidence

Diagnosis of B.1.616-related COVID-19 cases should not rely on RT-PCR tests on NP samples. In the epidemic area, strict infection control measures must be maintained as long as COVID-19 diagnosis is not ruled out, in order to limit nosocomial clusters and case fatality. Further studies are needed to confirm and investigate the association between genomic characteristics of B.1.616, and i) poor detection by RT-PCR tests on NP samples; ii) prognosis.