Background: Comparative data on the transmission of respiratory infections positive and negative for SARS-CoV-2 in households with children are limited.

Methods: In June-August 2020, we recruited 700 participants (175 households, 376 children, 324 adults) to be prospectively followed for all respiratory tract infections. Follow-up lasted from recruitment till April 2022. Daily symptoms were monitored by weekly electronic questionnaires. SARS-CoV-2 PCR testing from nasopharyngeal specimens was performed for symptomatic participants and twice (one-week interval) for the household members of positive participants. Clinical features and secondary attack rates (SARs), based on the onset of symptoms, were compared between SARS-CoV-2-positive and -negative respiratory infections.

Results: Most (90%) SARS-CoV-2 infections occurred from January to April 2022 when Omicron BA.1 and BA.2 were the dominant variants. SARS-CoV-2-positive infections were transmitted more often than SARS-CoV-2-negative infections (SAR, 41% vs 24%; P < .001). SARS-CoV-2 transmission was similar for child and adult index cases (SAR, 40% vs 43%; P = .47), but the transmission of SARS-CoV-2-negative infections was higher for child index cases (SAR, 27% vs 18%; P < .001).

Conclusions: Our findings demonstrate that SARS-CoV-2 Omicron viruses spread more effectively within households compared to other respiratory infections.