Table 1.

Nucleotide diversity of West Nile virus in Culex mosquitoes collected during the 2005, 2006 and 2007 transmission seasons from the suburban Chicago study area.

year	location	N	nucleotide diversity (%)	standard error (%)	differencea
2005	residential sites	76	0.37	0.022	p < 0.001
	natural sites	52	0.26	0.050
	all sites	128	0.33	0.016
2006	residential sites	59	0.45	0.023	p = 0.003
	natural sites	21	0.42	0.037
	all sites	80	0.44	0.019
2007	residential sites	38	0.50	0.039	p = 0.107
	natural sites	8	0.46	0.063
	all sites	46	0.50	0.035

^aStatistical difference between nucleotide diversity for viral sequences collected in residential versus natural sites within the same year, estimated from 10 000 bootstrap resamplings of the genetic distance matrices.