Ecological factors associated with pandemic influenza A (H1N1) hospitalization rates in California, USA: a geospatial analysis

Abstract

Abstract. The 2009 H1N1 influenza A virus subtype (H1N1) pandemic had a large impact in the United States of America (USA), causing an estimated 192,000 to 398,000 hospitalizations and 8,720 to 18,050 deaths between April 2009 and midMarch 2010. Recent research on the 2009 H1N1 pandemic has largely focused on individual, non-spatial demographic characterizations (e.g. age and race/ethnicity) associated with H1N1 hospitalizations. Broader ecological factors such as transportation use, land use and other socioeconomic factors are important aspects of influenza studies that have not been empirically examined. This research explores and identifies ecological factors associated with 2009 H1N1 pandemic hospitalization rates. We conducted a spatial regression analysis of county level hospitalization rates from 3 April to 15 September, 2009 obtained via the California Department of Public Health. Hospitalization rates were found to be spatially dependent. Public transportation usage rates and agricultural land use proportions were significant environmental factors positively related to hospitalization rates. Consistent with public health official's assumptions and existing evidence, county percentages of persons less than 18 years of age were positively associated with hospitalization. These findings help to clarify the limited consensus and dubious evidence on the role of broader ecological factors associated with pandemic influenza. A better understanding of the ecological risk factors associated with hospitalizations should also benefit public health officials with respect to their work aiming at improving emergency supply allocation and non-pharmaceutical intervention strategies in the context of an influenza pandemic.

Supply of Neuraminidase Inhibitors Related to Reduced Influenza A (H1N1) Mortality during the 2009–2010 H1N1 Pandemic: An Ecological Study

“…Additional differences in the susceptibility of a population to the pandemic H1N1 influenza virus may have biased an ecologic analysis, thus, data on at-risk populations, including the proportion of older individuals, degree of obesity, and pregnancy rate were considered. Further parameters, including public transportation usage and population density, were found to be related to hospitalization rates during the H1N1 pandemic in an ecologic analysis from California [20]. Population density was not found to be related to H1N1 mortality or NAI supply in this analysis, however.…”

“…Population density was not found to be related to H1N1 mortality or NAI supply in this analysis, however. It is likely that population density may have a greater impact on total hospitalizations and the spread of influenza, but that different factors related to health spending and health care infrastructure have a greater impact on H1N1 mortality, as was found in this analysis and by Nikolopoulos, et al [18] While every attempt was made to adjust for the many differences between Member States that could possibly bias an association between NAI supply and H1N1 mortality, the included co-factors were by no means exhaustive and several important confounders such as air quality or land use patterns – which may impact a population's susceptibility to influenza or exposure to infected livestock – may continue to bias the estimated main effect [18], [20]. Further, as with any ecological study, these associations may not be reflective of the individual-level association, and evidence from controlled studies is needed to evaluate the possibility of a causal relationship between NAIs and influenza mortality.…”

Spatiotemporal diffusion of influenza A (H1N1): Starting point and risk factors

“…According to Freedman and Leder [40], transport networks by virtue of direct contact with large numbers of individuals allow greater spread of pathogens and make populations exposed to public transport systems most susceptible to infection. Maliszewski e Wei [41] also found that public transport use rates were significantly and positively associated with hospitalization rates related to influenza A (H1N1) 2009 in California in the United States.…”

A longitudinal ecological study of seasonal influenza deaths in relation to climate conditions in the United States from 1999 through 2011

“…These results are consistent with a number of previous investigations examining demographic factors associated with influenza cases or deaths in temperate climates. For example, previous investigators examining ecological factors associated with pandemic influenza A (H1N1) hospitalization rates in the state of California revealed hospitalization rates were spatially dependent [18]. As another example, transmission of influenza A and B in a Pennsylvania school-based study population revealed that race was a significant mediating factor [19].…”