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Preventing SARS-CoV-2 Transmission in Health Care Settings in the Context of the Omicron Variant.

The world is in the midst of an unprecedented surge in SARS-CoV-2 cases attributable to the Omicron variant. This new variant is 2 to 3 times more contagious than the Delta variant. According to a report from the UK, 1109 of 14 606 non–household contacts of individuals with the Omicron variant developed infection vs 2922 of 102 997 non–household contacts of individuals with the Delta variant (7.6% vs 2.8%, respectively; adjusted odds ratio [OR], 2.63 [95% CI, 2.43-2.84]).1 The increased contagiousness of the Omicron variant is not only leading to a surge in community infections but it is also leading to more transmissions in hospitals. During the last week of December 2021 in England, for example, 2525 of 12 424 (20.3%) patients hospitalized with SARS-CoV-2 were first diagnosed more than 7 days after hospital admission. By comparison, the analogous figures for the first week of November 2021 were 434 of 5208 (8.3%) patients. The increase in hospital-onset infections associated with the Omicron variant belies the fact that nosocomial transmission of SARS-CoV-2 has been part of the COVID-19 pandemic from the beginning. The frequency of hospital-based transmission, however, is likely unappreciated. This is because few hospitals systematically test patients throughout and following their hospital stays. Most hospitals only test patients for SARSCoV-2 at the time of admission and therefore may miss some infections acquired after admission, especially because approximately 40% of SARS-CoV-2 infections are mild or asymptomatic and thus do not trigger repeat testing. Furthermore, hospital stays for many non–COVID19–related conditions are short, so some infections will only develop after discharge and will be missed or misattributed to posthospital exposures. Some jurisdictions have gone to great lengths to discern the true frequency of hospital-acquired SARSCoV-2. This is best done using whole-genome sequencing of the virus to demonstrate relatedness to the infections of other patients and staff as well as to eliminate spurious temporal and spatial associations. In a study from the University of Oxford that evaluated 803 inpatients and 329 staff members from 4 hospitals who were diagnosed with SARS-CoV-2 during a 7-week period in late 2020, an estimated 188 of 803 (23.4%) patient infections were deemed to potentially be nosocomial.2 Whole-genome sequencing helped identify multiple cases that were potentially acquired at the hospital despite receiving care on different wards (suggesting unidentified staff intermediaries) or being diagnosed at admission (suggesting exposure during a prior admission). Most hospitals have already implemented multifaceted infection control programs to prevent nosocomial SARS-CoV-2 transmission. These typically include universal mask wearing, strong encouragement or mandates for staff vaccination, requiring symptomatic staff members to stay home, contact tracing, and testing of all inpatients at admission. These measures have markedly reduced hospital-based transmissions, but the increase in nosocomial infections associated with the Omicron variant raises the urgent question of what more can be done to protect patients and staff. Hospitals could invoke 3 additional measures to further reduce the risk of nosocomial SARS-CoV-2 transmission as the Omicron variant continues to surge.