GIS expert Gonzalo Vazquez-Prokopec of Emory University in Atlanta conducted a spatial analysis for southeastern Atlanta that integrated the locations of so-called combined sewer overflow (CSO) systems – which channel wastewater to treatment plants – and any associated streams with six years worth of data on mosquito abundance and West Nile virus infections in mosquitoes, humans, blue jays and crows (these birds, which show high West Nile virus mortality, are used as sentinels for the disease).

The results showed higher rates of infection in all of the groups studied near all seven CSO facilities and associated streams, compared to those near urban creeks that weren’t affected by CSOs. The exception was humans living in wealthy areas, whose infection rates were unaffected by the proximity of a CSO.

During periods of heavy rain or snowmelt, wastewater flows from CSOs into waterways with minimal treatment. Previous research has shown that the virus’s mosquito vector thrives in streams contaminated by CSO discharges.

‘The infection rate for mosquitoes, birds and humans is strongly associated with their proximity to a creek impacted by sewage,’ said Vazquez-Prokopec. ‘And if the creek is in a low-income neighbourhood, we found that the entire cycle of infection is even higher.’

September 2010