Somewhat higher secondary attack rates
occurred among contacts who were family or household members of their source case-patient and among contacts of probable case-patients.
Although the overall 26% secondary attack rate
of laboratory-confirmed 2009 pandemic influenza A (H1N1) virus infection appears comparable to that for laboratory-confirmed seasonal influenza, more studies are needed to better understand the secondary attack rates
in both traditional and nontraditional household settings.
Household transmission of the 2009 pandemic A/ H1N1 influenza virus: elevated laboratory-confirmed secondary attack rates
and evidence of asymptomatic infections.
Sixth, the secondary attack rate
for cabin contacts may be an overestimate because passengers with negative NAT results were not tested for other respiratory infections, and passengers with onset of symptoms >24 hours after symptoms developed in a cabinmate were assumed to be secondary, rather than co-primary cases.
Because early case finding was most intensive among high school children associated with school outbreaks, our cohort may have been biased in favor of households where the index case-patients were children; however, this would not explain a lower secondary attack rate
among adult household contacts.
Secondary attack rate
for influenza A pandemic (H1N1) 2009, by travel history, Sichuan Province, China, June 2009 Group Total no.
cases of transmission 3 1 Time between carrier scan 2 h 17 min 32 min and case scan Hospital A A Secondary attack rate
, 60 (17.
Secondary attack rates
in susceptible persons are difficult to estimate and distinguish from carriage rates (2), and we varied these from 5% to 50%.
Among 3,916 contacts of the 1,099 primary case-patients, the crude secondary attack rate
Because of the low infectious dose of the agent (10-100 viral particles can induce symptoms), outbreaks are characterized by a high secondary attack rate
For 240 household members for whom information was available, rash that met the clinical case definition developed in 20 in 7 to 21 days after exposure to [is greater than or equal to] 1 index cases in a household (household secondary attack rate
Over the 4-year study period, the secondary attack rate
for colds in the intervention group was 7%, versus 20% in the control group.