title: The clustering and transmission dynamics of pandemic influenza A (H1N1) 2009 cases in Hong Kong.
abstract: OBJECTIVE
  Human influenza A (H1N1) 2009 has caused severe epidemics in many countries, but its dynamics in spatial and temporal contexts have so far been poorly appreciated.
  
  
  METHODS
  A total of 24,414 laboratory confirmed human influenza A (H1N1) 2009 cases reported from May to September 2009 in Hong Kong were evaluated, using a Geographic Information System (GIS)-based approach. Spatio-temporal clustering was assessed after dividing Hong Kong into 4 geographic sectors, 18 districts and 500 m × 500 m cells. Global Moran's I, Local Moran's I and SaTScan™ were used in the exploration.
  
  
  RESULTS
  Spatio-temporal clusters first appeared on Hong Kong Island at week 3, alongside multiple foci suggestive of infection nidus introduced from abroad. The clusters grew rapidly and became confluent in urban areas, lasting till week 22. Separately, local clusters emerged in the North representing second or third generation infections, which died down over a relatively short period of time.
  
  
  CONCLUSIONS
  Heterogeneity of spatio-temporal clustering of H1N1 was demonstrated during the epidemic, despite the small area of the territory of Hong Kong. The dynamics could have been shaped by population mobility at a local level. The application of GIS in epidemiology studies can add value to standard surveillance activities.
authors: Stanley Ho Centre for Emerging Infectious Diseases, The Chinese University of Hong Kong, Shatin, Hong Kong.
authors: Shui Shan
authors: SS
authors: Lee
authors: Ngai Sze
authors: NS
authors: Wong