Residential address errors in public health surveillance data: a description and analysis of the impact on geocoding

The residential addresses of persons with reportable communicable diseases are used increasingly for spatial monitoring and cluster detection, and public health may direct interventions based upon the results of routine spatial surveillance. There has been little assessment, however, of the quality of address data in reportable disease notifications and of the corresponding impact of these errors on geocoding and routine public health practices. The objectives of this study were to examine address errors for a selected reportable disease in a large urban center in Canada and to assess the impact of identified errors on geocoding and the estimated spatial distribution of the disease. We extracted data for all notifications of campylobacteriosis from the Montreal public health department from 1995 to 2008 and used an address verification algorithm to determine the validity of the residential address for each case and to suggest corrections for invalid addresses. We assessed the types of address errors as well as the resulting positional errors, calculating the distance between the original address and the correct address as well as changes in disease density. Address errors and missing addresses were prevalent in the public health records (10% and 5%, respectively) and they influenced the observed distribution of campylobacteriosis in Montreal, with address correction changing case location by a median of 1.1 km. Further examination of the extent of address errors in public health data is essential, as is the investigation of how these errors impact routine public health functions.

Quantitative studies on the peroxidation of human low-density lipoprotein initiated by superoxide and by charged and neutral alkylperoxyl radicals

Rates of peroxidation of human LDL and rates of consumption of the LDL's alpha-tocopherol (TocH) have been measured at 37 degrees C. Peroxidation was initiated by radicals generated in the aerated aqueous phase at known rates by thermal decomposition of appropriate precursors: superoxide (O2(*-)/HOO(*)) from a hyponitrite and alkylperoxyls (ROO(*), two positively charged, one negatively charged and one neutral) from azo compounds. The efficiencies of escape from the solvent cage of the geminate pair of neutral carbon-centered radicals was found to be 0.1, but it was 0.5 for the three charged radicals, a result attributed to radical/radical Coulombic repulsion within the cage. All four alkylperoxyls initiated and terminated tocopherol-mediated peroxidation (TMP) with about equal efficiency and essentially all of these radicals that were generated were consumed in these two reactions. TMP is a radical chain process, and when initiated by the alkylperoxyls, the rate of LDL peroxidation was faster in the early stages while TocH was present than later, after all of this "antioxidant" had been consumed. In contrast, only about 3-4% of the generated superoxide radicals reacted in any measurable fashion with TocH-containing LDL at pH's from 7.6 to 6.5 and peroxidation was much slower than with a similar rate of generation of alkylperoxyls. After all the TocH had been consumed, LDL peroxidation was negligible at pH 7.6 and 7.4, but at pH 6.8 and 6.5, the peroxidation rates showed a large increase over the rates while the TocH had been present. That is, endogenous TocH behaves as an antioxidant in LDL subjected to attack by the physiologically relevant superoxide radical, whereas TocH behaves as a prooxidant in LDL subjected to attack by the probably far less physiologically important alkylperoxyls. Rates of LDL peroxidation initiated by superoxide increased as the pH was decreased, and the results are consistent with the initiation of peroxidation of fresh LDL occurring via H-atom abstraction from TocH by HOO(*) to form the Toc(*) radical and termination by reaction of O2(*-) with Toc(*), a process that occurs partly by addition leading to TocH consumption and partly by electron plus proton transfer leading to the regeneration of TocH.