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. 2021 Apr:3:100038.
doi: 10.1016/j.lanepe.2021.100038. Epub 2021 Jan 22.

Infection and transmission of SARS-CoV-2 in London care homes reporting no cases or outbreaks of COVID-19: Prospective observational cohort study, England 2020

Anna Jeffery-Smith  1 , Kate Dun-Campbell  2 , Roshni Janarthanan  2 , Jonathan Fok  2 , Emma Crawley-Boevey  2 , Amoolya Vusirikala  2 , Elena Fernandez Ruiz De Olano  2 , Marina Sanchez Perez  2 , Suzanne Tang  2 , Thomas Aj Rowland  1 , Edward Wynne-Evans  2 , Anita Bell  2 , Bharat Patel  2 , Zahin Amin-Chowdhury  3 , Felicity Aiano  3 , Karthik Paranthaman  4 , Thomas Ma  4 , Maria Saavedra-Campos  4 , Joanna Ellis  1 , Angie Lackenby  1 , Heather Whitaker  1 , Richard Myers  1 , Katja Höschler  1 , Kevin Brown  3 , Mary E Ramsay  3 , Nandini Shetty  1 , J Yimmy Chow  2 , Shamez Ladhani  3   5 , Maria Zambon  1
Affiliations

Infection and transmission of SARS-CoV-2 in London care homes reporting no cases or outbreaks of COVID-19: Prospective observational cohort study, England 2020

Anna Jeffery-Smith et al. Lancet Reg Health Eur. 2021 Apr.

Abstract

Background: Care homes have been disproportionately affected by the COVID-19 pandemic. We investigated the potential role of asymptomatic infection and silent transmission in London care homes that reported no cases of COVID-19 during the first wave of the pandemic.

Methods: Five care homes with no cases and two care homes reporting a single case of COVID-19 (non-outbreak homes) were investigated with nasal swabbing for SARS-CoV-2 RT-PCR and serology for SARS-CoV-2 antibodies five weeks later. Whole genome sequencing (WGS) was performed on RT-PCR positive samples. Serology results were compared with those of six care homes with recognised outbreaks.

Findings: Across seven non-outbreak homes, 718 (387 staff, 331 residents) individuals had a nasal swab and 651 (386 staff, 265 residents) had follow-up serology. Sixteen individuals (13 residents, 3 staff) in five care homes with no reported cases were RT-PCR positive (care home positivity rates, 0 to 7.6%) compared to 13 individuals (3.0 and 10.8% positivity) in two homes reporting a single case.Seropositivity across these seven homes varied between 10.7-56.5%, with four exceeding community seroprevalence in London (14.8%). Seropositivity rates for staff and residents correlated significantly (rs 0.84, [95% CI 0.51-0.95] p <0.001) across the 13 homes. WGS identified multiple introductions into some homes and silent transmission of a single lineage between staff and residents in one home.

Interpretation: We found high rates of asymptomatic infection and transmission even in care homes with no COVID-19 cases. The higher seropositivity rates compared to RT-PCR positivity highlights the true extent of the silent outbreak.

Funding: PHE.

Keywords: Asymptomatic transmission; Care home; SARS-CoV-2 outbreak.

PubMed Disclaimer

Conflict of interest statement

The authors have nothing to disclose.

Figures

Fig 1
Fig. 1
Schematic of care home acute respiratory outbreaks (ARI; blue bars) and total COVID-19 related deaths in care homes in England (pink line) and London (yellow line) reported by ISO week of 2020. The enhanced outbreak testing periods for nasal swabbing SARS-CoV-2 RT-PCR - time-point 0 (T0) - and serology for SARS-CoV-2 antibodies – time-point 1 (T1) - are indicated for the care homes with outbreaks (phase 1 - red), single cases (phase 2 - amber) and those with no reported cases (phase 3 - green).
Fig. 2
Fig. 2
a) Summary data showing percentage IgG seropositivity against SARS-CoV-2 nucleocapsid (N) protein (Abbott®) and 95% confidence intervals for care home staff (left panel) and residents (right panel) for each care home (A-M). Dashed line indicates coincident estimated community seroprevalence in London [11]. b) Correlation of resident and staff seropositivity for each of the 13 care homes (Spearman rank correlation coefficient 0.84, p < 0.001). Colour coding: green = no cases reported at time of investigation; amber = single case reported; red = outbreak reported. Red defined as ‘outbreak’ homes; Amber and green homes defined as ‘non-outbreak’ homes.
Fig. 3
Fig. 3
a) Summary data showing IgG serostatus to SARS-CoV-2 N protein by age for non-outbreak care homes (left panel, N=651) and outbreak care homes (right panel, N=586). Statistical analysis using Kruskal-Wallis test non outbreak homes p=0.84. Statistical analysis using Kruskal-Wallis test outbreak homes p=0.58. b) Summary data showing SARS-CoV-2 recombinant N IgG index value (Abbott®) for all seropositive individuals (n=586) for all care homes. Kruskal Wallis test p=0.30. Age bracket of <60 applied to encompass majority of staff. Categories of 60-84 and ≥85 applied to separate residents based on frequency distribution of age of residents from across the cohort and mean age of 85 years.
Fig. 4
Fig. 4
Maximum likelihood phylogeny of 21 SARS-CoV-2 genomes from individuals across the six non-outbreak care homes with PCR positive individuals. Coloured shapes are used to indicate the care home, with circles denoting residents and triangles staff. The phylogenetic tree was rooted using the midpoint of the phylogeny.
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