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Our member Steve Cohen successfully defended his graduation thesis. Congratulations to Dr. Cohen!

Steve Cohen, DrPH, MPH, successfully defended his dissertation, entitled "Vaccination coverage in children and area sociodemographic characteristics associated with pneumonia and influenza in the United States elderly" at the Johns Hopkins Bloomberg School of Public Health on March 10, 2008. The abstract is as follows:

This dissertation seeks to explore, identify, and analyze the relationships between several population-level factors and influenza and pneumonia hospitalization patterns in the United States elderly. Influenza and pneumonia cause extensive morbidity and mortality, particularly in the older population.  A growing body of evidence suggests that one way to reduce the transmission of these deadly diseases to the vulnerable elderly is to target children for vaccination.  Using Medicare hospitalization data, influenza and pneumonia rate patterns in the elderly were assessed to determine their potential associations with state vaccination coverage in children and the elderly, along with related sociodemographic factors—income distribution, urbanicity, and grandparental caregiving practices.

This dissertation project was comprised of three related manuscripts. Manuscript One directly assessed vaccination coverage in children and the elderly and their associations with hospitalization patterns.  Two outcome variables were used—the conventional age-adjusted rates and a novel measure of the relative increase in disease rates with age—to account for and examine this important demographic component of disease at the state level.  Vaccination coverage in both children and the elderly were positively associated with age-adjusted disease rates. However, consistent negative associations were found between childhood vaccination coverage and the age increase in pneumonia and influenza rates.  This relationship was most evident in low-income and more urbanized states.  Although not conclusive, the abovementioned results suggest that vaccination of children is associated with reduced pneumonia and influenza levels in the elderly, particularly for the oldest elderly.  This observation may be especially important in low-income urban areas, although more research is needed to elucidate this relationship.

Manuscript Two explored the associations between several population-level sociodemographic factors and age patterns of influenza and pneumonia in the elderly on the county level.  The proportion of co-residential grandparents who provide care for their grandchildren was positively associated with elderly influenza and pneumonia rates.  Such relationship was present for all age groups, except for the oldest group.  Additionally, the highest influenza and pneumonia rates were found in the counties with the lowest levels of income.  Income inequality was also positively associated with disease rates, but only in low-income counties.  The findings highlight the need for further exploration of these potentially modifiable sociodemographic factors to reduce the burden of respiratory infections in the elderly.

Using a modified age-period-cohort approach, Manuscript Three focused on describing these three basic temporal and demographic factors that could potentially contribute to patterns of influenza and pneumonia in the elderly population.  Clear year-to-year differences in age-specific disease rates were observed, particularly for influenza alone.  As age increased, pneumonia and influenza rates also increased; age accounted for a substantial portion of the variation in rates.  However, the precise age-associated these trends were not consistent across influenza seasons, indicating that applying the same model age pattern to each influenza season may result in under- or overestimation of age-specific disease rates.  Differences in disease rates by cohort were also apparent.

Findings of this analysis suggest that several distinct and potentially modifiable factors related to socioeconomic and health policies should be addressed to prevent the spread of influenza and pneumonia to the vulnerable elderly population.  The results emphasize the value of assessing population-level factors that distally influence disease patterns to supplement traditional risk factor-based epidemiological studies of disease.  With rapid population aging and the growing threat of pandemic influenza, further research and subsequent policy development will become even more critical for the protection and health of the elderly.