Investigation of SARS-CoV-2 outbreak in UK office highlights the need for a site-specific COVID-19 prevention strategy

By Neha MathurFeb 4 2022Reviewed by Aimee Molineux

In a recent study posted to the medRxiv* pre-print server, a team of researchers comprehensively investigated a public-facing office in England where a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak occurred during August-September 2021 to identify workplace and worker-related risk factors.

The public office had implemented site-specific control measures to contain the spread of coronavirus disease 2019 (COVID-19). They had imparted COVID-19 training to workers, deployed commercial hand sanitizers, arranged for single occupancy desks with two-meter spacing, and placed plastic dividers between workers and the public.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

About the study

In the present study, the researchers conducted a comprehensive investigation of a three-story public sector facility (outbreak site) where a SARS-CoV-2 outbreak had occurred between August and September 2021. Later, a ‘circuit break’ closure was implemented at the outbreak site to stop transmission within the workplace.

The study team, COVID-19 Outbreak study Investigation to Understand Transmission (COVID-OUT), performed extensive investigations including surface sampling, environmental assessment, molecular and serological testing at the outbreak site between September and October 2021.

Of the 40 facility workers, 12 consented to participate in the COVID-OUT study. The participants completed online questionnaires, two rounds of SARS-CoV-2 antibody testing, and three rounds of the self-administered nose and throat swabs for quantitative reverse transcription-polymerase chain reaction (qRT-PCR) testing. 

To assess the ventilation conditions of the site, CO₂ measurements were used as a proxy; CO₂ concentrations were determined by spot measurements when the facility reopened with continuous measurements logged over the subsequent two-week period in selected locations. 

The researchers also performed two rounds of surface sampling - the first during the circuit break and the second round approximately two weeks after the site re-opened.

Findings

The results confirmed that despite strictly adhering to governmental COVID-19 control guidance and high vaccination coverage, a SARS-CoV-2 outbreak affected 55% of the workforce at the outbreak site, a three-story public sector facility. The overall SARS-CoV-2 attack rate was 55%, and it impacted 75% of cleaning staff, 47% of office staff, and 67% of security staff.

In total, 60 surfaces were tested at the outbreak site in the first round of sampling, of which 10 (16.7%) were confirmed positives, and one (1.7%) was a suspected positive. The surface sampling results highlighted that the security office was a site of enhanced contamination. Six of nine (66.7%) samples from this location tested positive, including three in the 32.0-34.9 C_t bracket. Therefore, before reopening, the site was extensively cleaned. Moreover, routine cleaning procedures were updated, especially for the confined security office area.

Although largely by natural means, the ventilation facilities at the site conformed with current guidance, including the security office. Therefore, CO₂ levels did not exceed 1200 ppm and typically were <700ppm. 

Of the 12 study participants, 41.7% (5/12) were SARS-CoV-2-positive during the outbreak period, as confirmed by COVID-OUT serological testing. All the participants, including the five SARS-CoV-2-positive cases, were immunized with two doses of COVID-19 vaccines. Additionally, SARS-CoV-2-positive individuals were symptomatic, displaying one of the following symptoms: fever, dry cough, productive cough, shortness of breath, and loss of taste or smell. 

Two-thirds of participants reported using face masks both at work and outside of work, with a higher proportion of non-cases using face masks nearly all the time. Two cases and two non-cases reported having direct physical contact with co-workers and the public. 

Conclusions 

Overall, the study findings highlighted the need for continually evolving, site-specific risk assessments that quickly adapt to changes in local community infection rates while recognizing heterogeneity within a workplace.

When this outbreak occurred, government guidelines did not mandate social distancing and mask usage. Over 75% of local residents had received two doses of COVID-19 vaccines before the outbreak. However, two weeks before the outbreak, government guidance was amended, and hence fully vaccinated people were not required to self-isolate even if they came in close contact with someone having COVID-19. Moreover, ventilation on site was adequate, predominately natural, with some forced mechanical general ventilation.

Despite being fully vaccinated, individuals contracted SARS-CoV-2 infections during this outbreak, thus reinforcing the significance of a multi-layered SARS-CoV-2 transmission mitigation strategy, in addition to vaccination. These strategies include appropriate transmission control measures, such as face masks, adequate ventilation, and social distancing to prevent severe COVID-19 illness and death.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.