Number Of Exposure Events Research Articles

Arterial Intima-Media Thickness in 13-Year-Old Adolescents and Previous Antichlamydial Antimicrobial Use: A Retrospective Follow-up Study

Children with persistent Chlamydia pneumoniae infection may be at increased risk for atherosclerosis. The impact of antimicrobial therapy for primary prevention of atherosclerotic cardiovascular disease is unsolved. The purpose of this study was to determine whether treatment with antimicrobial agents effective against C pneumoniae during childhood, regardless of indication, has a favorable influence on the arterial wall-thickness in children by the time they reach adolescence. The association of macrolide, tetracycline, quinolone, and rifamycin use (number of exposure events) between ages 5 and 13 years with carotid and aortic intima-media thickness at age 13 years was investigated among 508 healthy children. Information about the use of medications was obtained from the Finnish prescription register. Arterial intima-media thickness was measured with a high-resolution ultrasound. Mean aortic intima-media thickness showed a significant direct association with the number of antichlamydial antimicrobial exposure events also after controlling for established atherosclerotic risk factors. Elevated C-reactive protein level had an additional effect on aortic intima-media thickness in a multivariable model. Carotid intima-media thickness was not associated with the number of preceding antichlamydial treatments. Recurrent antichlamydial treatments in childhood have no favorable influence on early vascular changes but are associated with increased intima-media thickness in the abdominal aorta. These findings suggest that the use of antimicrobial agents does not offer protection against the potential atherogenicity of repeated infectious insults.

Estimating exposure point concentrations for surface soils for use in deterministic and probabilistic risk assessments

When estimating human or ecological risks from exposures to surface soils at terrestrial properties regulated as hazardous waste sites by federal or state agencies, risk assessors must estimate exposure point concentrations (EPCs) for compounds in the surface soils. In this manuscript, we demonstrate non‐parametric methods to estimate the EPC for a single compound in surface soils for use in deterministic and/or probabilistic human or ecological risk assessments. Since regulatory agencies instruct risk assessors to consider scenarios involving long‐term (chronic or lifetime) average exposures in most human risk assessments (USEPA, 1992, Exposure; Lioy, 1990; USEPA, 1989, HHEM), it is essential to distinguish (i) the number of soil samples taken in the field program, Ns, for which the field geologist has laboratory measurements from (ii) the number of exposure events, Ne (>>Ns) over which the exposure is properly averaged. By taking spatial information into account, we demonstrate new methods for computing the upper 95th‐percentile of the uncertainty in the mean concentration that overcome the limitations in the method currently recommended by the US Environmental Protection Agency for deterministic human risk assessments. We also extend the new methods to developing EPCs for multiple compounds and to developing second‐order distributions for use in probabilistic risk assessments.