Background: The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), led to global actions to limit the transmission. Extensive testing quickly led to a worldwide shortage of testing equipment, including nasopharyngeal swabs (NPS), warranting novel specimen collection methods. Social restrictions were implemented on children, although the children’s role in the household transmission of respiratory infections, both negative and positive for SARS-CoV-2, is lacking. This thesis was conducted to investigate novel specimen collection methods and household transmission of SARS-CoV-2.

Methods: We assessed the performance of saliva and Finswab, NPS made via plastic injection molding, compared to a reference NPS for SARS-CoV-2 detection. Household transmission of SARS-CoV-2 was examined by prospectively following acute respiratory tract infections in 700 participants in 175 households with school-aged children. Symptomatic and exposed participants were tested by SARS-CoV-2 PCR, and SARS-CoV-2 antibodies were determined five weeks after SARS-CoV-2 infection in household. Secondary attack rates were calculated.

Results: The number of virus-positive cases for Finswab and reference swab, and for saliva and NPS, were similar. SARS-CoV-2 CT values for saliva were higher compared to NPS. Most (90%) SARS-CoV-2 infections occurred from January to April 2022, when Omicron BA.1 and BA.2 were dominant variants. SARS-CoV-2–positive infections were transmitted more often than other respiratory infections, i.e. SARS-CoV-2–negative infections. Transmission of SARS-CoV-2–negative infections, but not that of SARS-CoV-2–positive infections, was higher for child index cases.

Conclusions: Finswab and saliva are both viable alternatives to the routinely used flocked nylon NPS in SARS-CoV-2 diagnostics. The household transmission of SARS-CoV-2 Omicron variants was higher compared to other respiratory infections, with children being more infective than adults only for SARS-CoV-2-negative infections.