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J Infect
. 2026 Apr 20:106748.
doi: 10.1016/j.jinf.2026.106748. Online ahead of print.
INFLUENZA HOUSEHOLD TRANSMISSION AND GENOMIC DIVERSITY IN THE UNITED STATES: A PROSPECTIVE COHORT STUDY, 2022-2024
Sarah N Cox 1 , Julia C Bennett 1 , Amanda M Casto 2 , Katherine L Hoffman 3 , Collrane Frivold 1 , Marco Carone 3 , Zack Acker 4 , Tara M Babu 2 , Cassandra L Boisvert 5 , Brenna Ehmen 4 , Janet A Englund 6 , Sally Grindstaff 4 , Peter Han 4 , Tara L Hatchie 2 , Jennifer L Kuntz 5 , Christina M Lockwood 7 , Kathryn M McCaffrey 4 , Richard A Mularski 5 , Lani Regelbrugge 4 , Sacha Reich 5 , Mark A Schmidt 5 , Ning Smith 5 , Lea Starita 8 , Jeremy Stone 4 , Alexandra Varga 5 , Ana A Weil 9 , Allison L Naleway 5 , Helen Y Chu 10
Affiliations
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.
Keywords: adolescent; adult; community surveillance; epidemiology; genomics; household transmission; influenza; pediatric.
. 2026 Apr 20:106748.
doi: 10.1016/j.jinf.2026.106748. Online ahead of print.
INFLUENZA HOUSEHOLD TRANSMISSION AND GENOMIC DIVERSITY IN THE UNITED STATES: A PROSPECTIVE COHORT STUDY, 2022-2024
Sarah N Cox 1 , Julia C Bennett 1 , Amanda M Casto 2 , Katherine L Hoffman 3 , Collrane Frivold 1 , Marco Carone 3 , Zack Acker 4 , Tara M Babu 2 , Cassandra L Boisvert 5 , Brenna Ehmen 4 , Janet A Englund 6 , Sally Grindstaff 4 , Peter Han 4 , Tara L Hatchie 2 , Jennifer L Kuntz 5 , Christina M Lockwood 7 , Kathryn M McCaffrey 4 , Richard A Mularski 5 , Lani Regelbrugge 4 , Sacha Reich 5 , Mark A Schmidt 5 , Ning Smith 5 , Lea Starita 8 , Jeremy Stone 4 , Alexandra Varga 5 , Ana A Weil 9 , Allison L Naleway 5 , Helen Y Chu 10
Affiliations
- PMID: 42019633
- DOI: 10.1016/j.jinf.2026.106748
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.
Keywords: adolescent; adult; community surveillance; epidemiology; genomics; household transmission; influenza; pediatric.