Table 2. West Nile virus (WNV)–positive mosquito pools, by species, United States, 2001–2004*.

2001		2002		2003		2004 (through 11/30/2004)
Positive pools, n = 612†		Positive pools, n = 3,720†		Positive pools, n = 5,538†		Positive pools, n = 4,755†
Species	% of pools	Species	% of pools	Species	% of pools	Species	% of pools
Culex pipiens	57.0	Cx. pipiens	47.0	Cx. tarsalis	31.5	Cx. quinquefasciatus	51.4
Cx. restuans	12.4	Cx. quinquefasciatus	19.1	Cx. pipiens	20.8	Cx. tarsalis	20.4
Cx. salinarius	11.4	Cx. restuans	9.1	Cx. quinquefasciatus	19.1	Cx. pipiens	12.7
Culiseta melanura	4.2	Cx. tarsalis	7.6	Cx. restuans	15.3	Cx. restuans	4.4
Cx. quinquefasciatus	2.1	Cx. salinarius	3.6	Cx. salinarius	4.5	Cx. erythrothorax	3.6
Ochlerotatus. triseriatus	2.1	Aedes albopictus	2.0	Ae. vexans	2.3
21 other species‡	10.6	23 other species‡	11.5	35 other species‡	6.4	35 other species‡	7.5

*Data were derived from reports submitted by state health departments to the Centers for Disease Control and Prevention's Arbonet surveillance system. Mosquito specimens were collected, identified, and tested in the respective state surveillance systems. Pools were reported as positive if they contained detectable levels of one of the following: infectious WNV, WNV RNA, WN viral antigen.
†Includes only WNV-positive pools reported as monospecific, i.e., excludes mixed pools (e.g., Cx. pipiens/restuans) or pools identified only to genus (e.g., Culex species).
‡No other species individually comprised ≥2.0% of the WNV-positive pools.