Factors associated with household transmission of SARS-CoV-2 omicron variant to health care workers: A retrospective cohort study

AimThe aim of this study was to determine the risk factors for household transmission of the omicron variant of SARS-CoV-2.BackgroundThe household infection rate has been reported to be higher for the omicron variant than for non-omicron variants of SARS-CoV-2. Determination of the risk factors for household transmission of the omicron variant is therefore important.DesignA Retrospective Cohort Study was conducted.MethodsWhen family members of health care workers (HCWs) were found to be infected with SARS-CoV-2, the HCWs had to receive two nucleic acid amplification tests for SARS-CoV-2: immediately after and 5 to 10 days after the onset of COVID-19 in the family members. Risk factors of household transmission were analysed by comparing cases (HCWs infected with SARS-CoV-2) and controls (HCWs not infected with SARS-CoV-2) using multivariable analysis.ResultsUnvaccinated status (OR: 3.97), age of index cases (<= 6 years) (OR: 1.94) and staying at home with index cases (OR: 10.18) were risk factors for household transmission.ConclusionIf there is a strong desire to avoid household infection, family members infected with SARS-CoV-2 should live separately during the period of viral shedding. What is already known about this topic?During the COVID-19 pandemic, nurses have been exposed to SARS-CoV-2 not only from COVID-19 patients but also from family members infected with SARS-CoV-2 but prevention of SARS-CoV-2 infection to nurses is important to maintain health services function.The household infection rate was reported to be higher for the omicron variant (42.7%) than for non-omicron variants (36.4% for Alpha, 29.7% for Delta and 22.5% for Beta). Determination of the risk factors for household transmission of the omicron variant is therefore important.What this paper adds?Unvaccinated HCWs had higher transmission rates (OR: 3.97, 95% CI: 1.22-12.88) than those of HCWs who received more than two doses of BNT162b2 or mRNA-1273 mRNA COVID-19 vaccines.Index cases aged 6 years or younger had higher transmission rates (OR: 1.94, 95% CI: 1.13-3.35) than those of index cases aged 7 years or older.The odds of transmitting to HCWs was higher (OR: 10.18, 95% CI: 2.98-34.72) for HCWs who stayed at home with the index cases than for HCWs who spent time in a different building from the index cases.The implications of this paper:If there is a strong desire to avoid household infection, family members infected with SARS-CoV-2 should live separately during the period of viral shedding.