Prospective cohort study uncovers a 9.5% secondary influenza attack rate in households, indicating that symptomatic children with high viral loads drive domestic viral transmission.
OBJECTIVES: To analyze the extent and risk factors of household influenza transmission using molecular testing and viral genomes. METHODS: In a community-based cohort in the United States during 2022-2024, participants self-collected weekly nasal swabs. Swabs were tested for influenza by RT-PCR; genomic sequencing was performed. Index cases had the first influenza detection within households. Factors associated with household transmission were evaluated using Poisson regression. RESULTS: Influenza transmission was detected in 56/303 influenza-positive households with a distinct index case. Most (82%) index cases were symptomatic; 16% of children vs 28% of adults were asymptomatic. 89/941 household contacts were infected 1-7 days after the index (secondary household infection risk: 9.5%, 95% CI: 7.3, 12.2). Index and secondary case median ages were 11 and 24 years, respectively. A greater proportion of contacts were infected when the index case was symptomatic (11%) vs asymptomatic (5%). Higher viral load was associated with 3.1 (1.7, 5.8) times higher risk of secondary infection. Most (13/16) index-secondary case pairs with available sequences differed by ≤3 nucleotides. CONCLUSIONS: Most household index cases were symptomatic children. Higher viral load and presence of symptoms among index cases were associated with household transmission. Home-based surveillance can assess household transmission using case chronology and genomics.
No takes yet. Share an insight, caveat, or question.
Cox et al. (2026) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: