Spatial analysis of respiratory disease on an urbanized geothermal field

Chronic exposure to hydrogen sulfide (H(2)S) in the parts per billion-parts per million range occurs in the population of Rotorua, a city built upon an actively degassing geothermal field in the Taupo Volcanic Zone, New Zealand. H(2)S is acutely toxic at high concentrations but little is understood of the health effects of chronic, low-level exposure. In Rotorua, H(2)S emissions and ambient concentrations are heterogeneous and approximately 30% of the greater urban area's population live upon or <4 km downwind of the geothermal field. Spatial analysis of disease incidence clustering using a spatial scan statistic is a powerful tool with which to investigate the spatial relationship which may exist between H(2)S and respiratory disease. This paper reports findings from a spatial cluster analysis of 11 years of hospital discharge data at the census area unit resolution. Results indicate that the relative risk (RR) of incidence of noninfectious respiratory diseases may be substantially higher among residents living in the geothermal area than have been reported previously. RR >5 for chronic obstructive pulmonary disease and its associated conditions are found in clusters which are spatially coincident with the geothermal field. Future work which investigates neurological and circulatory disease groups at the same or better spatial resolution may provide further insight into the chronic health effects of H(2)S exposure than these preliminary findings indicate.