title: Modification by influenza on health effects of air pollution in Hong Kong.
abstract: BACKGROUND
  Both influenza viruses and air pollutants have been well documented as major hazards to human health, but few epidemiologic studies have assessed effect modification of influenza on health effects of ambient air pollutants.
  
  
  OBJECTIVE
  We aimed to assess modifying effects of influenza on health effects of ambient air pollutants.
  
  
  METHODS
  We applied Poisson regression to daily numbers of hospitalizations and mortality to develop core models after adjustment for potential time-varying confounding variables. We assessed modification of influenza by adding variables for concentrations of single ambient air pollutants and proportions of influenza-positive specimens (influenza intensity) and their cross-product terms.
  
  
  RESULTS
  We found significant effect modification of influenza (p < 0.05) for effects of ozone. When influenza intensity is assumed to increase from 0% to 10%, the excess risks per 10-microg/m(3) increase in concentration of O(3) increased 0.24% and 0.40% for hospitalization of respiratory disease in the all-ages group and >or= 65 year age group, respectively; 0.46% for hospitalization of acute respiratory disease in the all-ages group; and 0.40% for hospitalization of chronic obstructive pulmonary disease in the >or= 65 group. The estimated increases in the excess risks for mortality of respiratory disease and chronic obstructive pulmonary disease in the all-ages group were 0.59% and 1.05%, respectively. We found no significant modification of influenza on effects of other pollutants in most disease outcomes under study.
  
  
  CONCLUSIONS
  Influenza activity could be an effect modifier for the health effects of air pollutants particularly for O(3) and should be considered in the studies for short-term effects of air pollutants on health.
authors.affiliation: Department of Community Medicine and School of Public Health, University of Hong Kong, Hong Kong Special Administration Region, People's Republic of China.
authors.forename: Chit Ming
authors.initials: CM
authors.lastname: Wong
authors.forename: Lin
authors.initials: L
authors.lastname: Yang
authors.forename: Thuan Quoc
authors.initials: TQ
authors.lastname: Thach
authors.forename: Patsy Yuen Kwan
authors.initials: PY
authors.lastname: Chau
authors.forename: King Pan
authors.initials: KP
authors.lastname: Chan
authors.forename: G Neil
authors.initials: GN
authors.lastname: Thomas
authors.forename: Tai Hing
authors.initials: TH
authors.lastname: Lam
authors.forename: Tze Wai
authors.initials: TW
authors.lastname: Wong
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Hedley
authors.forename: J S Malik
authors.initials: JS
authors.lastname: Peiris
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000397:Air Pollution / Q000009:adverse effects*; D002318:Cardiovascular Diseases / Q000401:mortality; D002648:Child; D002675:Child, Preschool; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007251:Influenza, Human / Q000453:epidemiology* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010126:Ozone / Q000633:toxicity; D012044:Regression Analysis; D012120:Respiration Disorders / Q000401:mortality; D012307:Risk Factors; D055815:Young Adult
chemical_list: D010126:Ozone