242521 Novel Statistical Approach for Identification of Household Secondary Attack Rate During Pandemic H1N1 in Los Angeles County

Wednesday, November 2, 2011: 11:10 AM

Jonathan Sugimoto, PhD, MHS , Fred Hutchinson Cancer Research Center, Center for Statistics and Quantitative Infectious Diseases, Seattle, WA
Brandon Dean, MPH , Emergency Preparedness and Response, County of Los Angeles-Department of Public Health, Los Angeles, CA
Background: Household secondary attack rate (SAR) estimates for symptomatic pandemic influenza A (H1N1) 2009 (pH1N1) were lower than expected given the speed of spread within communities worldwide. Methods: Our work demonstrates a novel statistical method accounting for confounding by unobserved immunity and asymptomatic infection. We provide the first SAR for pH1N1 infection estimated without serological confirmation. We estimate age, sex, and antiviral prophylaxis effects for transmission. Results: Ninety-nine symptomatic pH1N1 cases occurred among the 299 members of 58 households during the Spring of 2009. The SAR for symptomatic pH1N1 was 7% (95% confidence interval [CI]: 5%-10%), whereas the SAR for pH1N1 infection was 37% (95% CI: 18-62). Children (<18 years) were 2.5-times (95% CI: 1.2-5.0) more susceptible than adults (≥18 years) to symptomatic pH1N1. The age-group odds ratio for pH1N1 infection was 4.4 (95% CI: 1.4-13.4). Prophylactic antiviral efficacy was 42% for symptomatic pH1N1 and 21% for infection. Conclusions: The SAR for symptomatic pH1N1 is confounded by unobserved immunity and asymptomatic infection. Age is an important determinant of susceptibility. Our novel method extracts additional information from data routinely-collected for outbreak investigations, so we advocate its application in other transmission investigations. Further prospective cohort studies of influenza transmission are needed.

Learning Areas:
Protection of the public in relation to communicable diseases including prevention or control

Learning Objectives:
1-Define novel statistical method used to identify household secondary attack rate for symptomatic pandemic H1N1 in Los Angeles County. 2-Identify and discuss lessons learned and operational barriers to implementation of novel disease investigation approach in Los Angeles. 3-Identify opportunities and benefits of this statistical approach to improve epidemiological based decision making capabilities; in other jurisdictions and for other communicable disease investigations and analysis.

Keywords: Data/Surveillance, Infectious Diseases

Presenting author's disclosure statement:

Qualified on the content I am responsible for because: Postdoctoral Fellow with Center for Statistics and Quantitative Infectious Diseases-Vaccine and Infectious Disease Institute, working to develop more applicable and effective emergency public health preparedness tools and measures for local implementation in Los Angeles County for 3 years.
Any relevant financial relationships? No

I agree to comply with the American Public Health Association Conflict of Interest and Commercial Support Guidelines, and to disclose to the participants any off-label or experimental uses of a commercial product or service discussed in my presentation.