The CDC’s Emerging Infections Diseases journal will publish in April a study (PDF file) examining household transmission of H1N1.
The investigators tracked patients in San Antonio, TX, (in April and May of 2009) who had lab-confirmed H1N1. They also recorded any “secondary case-patients” among housemates of the flu sufferers — i.e., people who were (presumably) sickened by their H1N1-infected housemates.
The study concludes that children (people under 18) were “disproportionately affected” by H1N1:
The highest proportion of laboratory-confirmed pandemic (H1N1) 2009 and secondary attack rates occurred in children, a finding consistent with the epidemiology of seasonal and pandemic influenza, where we know children experience higher rates of illness [...] and higher secondary attack rates [...]
It also determines that the “secondary attack rate” (contagiousness) appeared to be lower than for seasonal flu:
The secondary attack rate was 4% for laboratory-confirmed pandemic (H1N1) 2009, 9% for ILI [influenza-like illness], and 13% for ARI [acute respiratory infection]. In general, these rates are lower than for seasonal influenza and lower than anticipated for a pandemic strain [...].
You can read up on the full scope and “several limitations” of the study here (PDF file).












