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Abstract #162817

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Eric Lofgren, BA¹, Nina Fefferman², Yuri N. Naumov, PhD³, Jack Gorski, Pd D⁴, and Elena Naumova, PhD². (1) School of Public Health, Department of Epidemiology, University of North Carolina - Chapel Hill, 100-301 Timber Hollow Ct., Chapel Hil, NC 27514, 303-912-2595, Eric.Lofgren@unc.edu, (2) Department of Public Health and Family Medicine, Tufts University, 136 Harrison Avenue, Boston, MA 02111, (3) Pathology, University of Massachusetts, S2-135, 55 Lake Avenue North, Worcester, MA 01605, (4) Blood Research Institute, BloodCenter of Wisconsin, P.O. Box 2178, Milwaukee, WI 53201

The seasonal occurrence of influenza is well characterized, but lacks a definitive cause. Seasonal variations in P&I mortality in Wisconsin between 1967 and 2004 was examined, with respect to the dominant circulating strains of H3N2, H1N1 and B influenzas.

Using Poisson regression adapted for time series analysis, annual epidemic curve characteristics for outbreak timing, amplitude, duration and average mortality rates were estimated. The characteristics for three population subgroups, 65+ years, 6-64 years and 0-5 years were compared to known circulating strains using ANOVA.

From 1967 to 1969, the A/Hong Kong/1/68 pandemic strain was responsible for an increase in mortality of 1.93 deaths/million in 0 to 5 and 0.58 deaths/millions in those 6 to 64, compared to the average rate throughout the duration of the series (Tukey's HSD, α=0.10). No rise was seen in the 65+ mortality rate; however, it was higher for an 11 year period between 1986 and 1996, when H1N1 viruses of the A/Singapore/6/86-like strain circulated. During this period, the average mortality rate in this subgroup increased by 1.98 deaths/million (Tukey's HSD, α=0.10) compared to the average.

The A/Singapore/6/86 strain, associated with increased mortality for those 65 and older, though showing no increase in other subgroups, was not previously noted for pandemic potential or heightened virulence. These findings suggest that further attention should be given to the role of individual viruses in annual epidemics, as well as the potential impact of a patient's age and immunological history in determining the severity of the disease in a population.

Learning Objectives:

• Describe the potential impact of viral evolution on the seasonal incidence of influenza
• Recognize the importance of inter-year variation in seasonal influenza
• Apply the discussed techniques to other applications in disease epidemiology

Keywords: Epidemiology, Infectious Diseases

Presenting author's disclosure statement:

Any relevant financial relationships? No
Any institutionally-contracted trials related to this submission?

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.

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