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--APHA 134th Annual Meeting
--4 - 8 November 2006,
--Boston, Massachusetts

Our three research papers have been selected as oral presentations for the American Public Health Association 134th Annual Meeting, one of the largest public health events in the U.S.

Association of influenza seasonality with temperature and temperature-related indicators
Eric Lofgren, Nina Fefferman, PhD, Jack Gorski, PdD, and Elena Naumova, PhD

Influenza seasonality is one of the best characterized, and least understood, aspects of the dynamics of non-pandemic influenza infection. One factor frequently cited, but rarely rigorously examined in existing literature is the association of seasonal infection rates with ambient temperature and temperature-related factors.

An extensive data set of 2619 laboratory confirmed cases of influenza in Milwaukee, Wisconsin, adjusted for population, was analyzed against an array of climatological variables obtained from NOAA for the period between January 1967 and June 2005. Using regression modeling adapted for time series studies and contour mapping techniques, the relationship between influenza incidence and temperature related indicators was elucidated.

Influenza A infection was found to be strongly associated with a decrease in monthly temperature (r=0.418, p <.0001). More refined examination of these relationships revealed that incidence was greatest in the month subsequent to the coldest month of the year (18.1 ± 3.7 cases/million persons/month), and during relatively warm winters. The typical two-year cycle of seasonality was not observed in this data, and Influenza B had a two month delay in occurrence when compared to Influenza A.

These preliminary results suggest a far more complex relationship between virus, host and environment than had been previously been considered in the context of seasonality. We are supplementing the analysis with influenza mortality and hospitalization data to further explore the full nature of Influenza seasonality, on an epidemiological, mathematical, and virological level.

Environmental indicators for clostridium difficile in the US elderly
Jyotsna Jagai, MS, MPH, Anna Kosheleva, MS, Denise Castronovo, MS, and Elena Naumova, PhD

The incidence of Clostridium difficile associated diarrhea has risen over the past two decades and in the US more than 300,000 cases per year occur in hospitals or long-term care facilities. C. difficile is associated with antibiotic use and up to 75% of cases of antibiotic associated diarrhea are attributable to C. difficile. It is plausible that spatio-temproal patterns could be driven by pathogens for which antibiotics are prescribed. The presence of pathogens and their pathogenicity can be driven by environmental factors and may differ by climate zones. Therefore, we hypothesize that rates of C. difficile are associated with meteorological characteristics in different climate zones. All hospitalization records for C. difficile, as well as non-specific gastroenteritis infections and symptoms from the Centers for Medicare and Medicaid Services (CMS) MedPAR data file for a 5 year period (1998-2002) were abstracted. Annual rates were calculated for each county (3108) and each county was classified based on the Koppen Climate classification scheme and assigned to a watershed region. We compared the rates across climate categories and watersheds using ANOVA. The average annual county-specific hospitalization rate of C. difficile per 100,000 elderly was 234.59 ± 160.40 cases. The highest rates were seen in the humid climate region which covers the US Midwest (301.75 ± 182.34) and in the Ohio Region watershed (355.48 ± 167.94). Rates were also correlated with non-specific gastroenteritis (Pearson r = 0.345). These preliminary results suggest that higher rates of C. difficile are associated with climate-sensitive environmental characteristics.

Preexisting rate of gastroenteric infections among elderly residing in areas affected by Hurricane Katrina
Kenneth K. H. Chui, MS, MPH, Anna Kosheleva, MS, Jyotsna Jagai, MS, MPH, Denise Castronovo, MS, and Elena Naumova, PhD

An increase in gastroenteric infections (GI) associated with microbial contaminations in water supply has been noted during warm and rainy seasons worldwide. Vulnerable populations residing in areas prone to severe rainfall are likely to be exposed to contaminated water and display higher incidence of GI rates. Attempting to document historical status of GI among elderly (≥65yo) in the areas affected by Hurricane Katrina in Louisiana and Mississippi, we gathered information from various sources and described GI rates for the two states from 1998 to 2002. We abstracted and aggregated GI counts from the Centers for Medicare and Medicaid Services database at the zip code level. Results were geo-merged with Census 2000 data on Zip Code Tabulation Area level (ZCTA) using zip code centroids for annual rate calculation (cases/1000 population) and demographic comparisons. Both states provided information on areas flooded by Katrina. Geographic distribution of GI rates are shown using maps created with ArcInfo 8.3. In the 989 ZCTAs, elderly composed of 13 ± 6% of the population, ranging from 0% to 70%. Seventeen ZCTAs flooded by Katrina in Louisiana had similar percentage of elderly (11% ± 3%, p = 0.15) but higher population density (2600 vs. 200 person/km2, p < 0.001) and larger proportion of African Americans (66% vs. 26%, p < 0.001). Overall GI rates (ICD9: 001 to 009) among ≥65yo were similar between the flooded and non-flooded areas (0.17 vs. 0.25 per 1000 of population ≥65yo, p = 0.10).