title: Does chronic exposure to high levels of nitrogen dioxide exacerbate the short-term effects of airborne particles?
abstract: BACKGROUND
  Long-term exposure to air pollutants has been hypothesised as a factor in susceptibility to short-term exposure to particulate matter (PM), but results are not coherent. We studied the short-term effects of PM10on mortality and assessed whether long-term exposure to nitrogen dioxide (NO2) modifies this association.
  
  
  METHODS
  We used a case-crossover design to evaluate daily PM10-related mortality among 124 432 35+ year-old participants who died in Rome between 2001 and 2010 and maintained the same address for at least 5 years before death. Modification of PM10-related mortality by long-term NO2exposure was determined by two-way interaction, while a three-way interaction was used to assess effect modification of high NO2levels in population groups defined by sociodemographic position and pre-existing diseases.
  
  
  RESULTS
  Mortality increased by 0.82% (0.23-1.41%) for each 10 µg/m3increase in PM10. Mortality rose by 1.22% (0.17-2.38%) in participants exposed to NO2levels ≥50 µg/m3and by 0.69% (0.03-1.34%) in those exposed to levels <50 µg/m3with no effect modification (p-interaction 0.378). A suggestion of effect modification was seen in 85+-year-olds (3.10%; p-interaction 0.043), as well as in those with a pre-existing arrhythmia (3.26%; p-interaction 0.014) and chronic obstructive pulmonary disease (3.52%; p-interaction 0.042).
  
  
  CONCLUSIONS
  Long-term exposure to NO2is not likely to induce susceptibility to short-term PM10exposure in the overall population. However, an effect modification of NO2is probable in the elderly and in those suffering from arrhythmias and chronic obstructive pulmonary disease.
authors: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy.
authors: Annunziata
authors: A
authors: Faustini
authors: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy.
authors: Massimo
authors: M
authors: Stafoggia
authors: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy.
authors: Matteo
authors: M
authors: Renzi
authors: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy.
authors: Giulia
authors: G
authors: Cesaroni
authors: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy.
authors: Ester
authors: E
authors: Alessandrini
authors: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy.
authors: Marina
authors: M
authors: Davoli
authors: Department of Epidemiology, Lazio Regional Health Service, Rome, Italy.
authors: Francesco
authors: F
authors: Forastiere
mesh_terms: D000328:Adult; D000393:Air Pollutants / Q000009:adverse effects* / Q000032:analysis; D000397:Air Pollution / Q000009:adverse effects* / Q000032:analysis; D018592:Cross-Over Studies; D004781:Environmental Exposure / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009026:Mortality; D009585:Nitrogen Dioxide / Q000009:adverse effects*; D010316:Particle Size; D052638:Particulate Matter / Q000009:adverse effects* / Q000032:analysis; D012044:Regression Analysis; D012307:Risk Factors; D012384:Rome / Q000453:epidemiology; D012959:Socioeconomic Factors; D013997:Time Factors
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter; D009585:Nitrogen Dioxide
keywords: additive effect; effect modification; long-term NO2; mortality; short-term PM exposure