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Volume 16, Number 3—March 2010

Research

Surveillance for West Nile Virus in American White Pelicans, Montana, USA, 2006–2007

Gregory JohnsonComments to Author , Nicole Nemeth, Kristina Hale, Nicole Lindsey, Nicholas Panella, and Nicholas Komar
Author affiliations: Montana State University, Bozeman, Montana, USA (G. Johnson, K. Hale); Centers for Disease Control and Prevention, Fort Collins, Colorado, USA (N. Nemeth, N. Lindsey, N. Panella, N. Komar)

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Table 2

Culex tarsalis mosquito infection data for WNV calculated weekly during 2 WNV transmission seasons, Medicine Lake National Wildlife Refuge, Montana, USA*

Week of collection 2006
2007
Light trap nights Light trap index ± SD† No. positive pools/no. tested Light trap nights Light trap index ± SD† No. positive pools/no. tested Infection rate‡ (95% CI) Vector index§ (95% CI)
Jul 1–7 13 4.1 ± 4.3 0/17 4 448.5 ± 549.5 0/100 0.0 0.0
Jul 8–14 9 6.6 ± 11.6 0/59 9 325.3 ± 131.4 5/800 6.3 (0.8–11.7) 2.0 (0.3–3.8)
Jul 15–21 10 9.0 ± 8.8 0/88 10 1,643.0 ± 899.8 7/1,000 7.0 (1.8–12.2) 11.5 (3.0–20.0)
Jul 22–28 11 7.0 ± 5.9 0/69 8 259.6 ± 301.9 4/1,000 4.0 (0.1–7.9) 1.0 (0.03–2.1)
Jul 29–Aug 4 13 7.1 ± 10.4 0/74 7 169.0 ± 105.3 10/937 10.7 (4.1–17.3) 1.8 (0.7–2.9)

*WNV, West Nile virus: CI, confidence interval.
†Light trap index is mean number of adult female Cx. tarsalis mosquitoes collected per trap night. Seven traps were used in 2006, and 5 traps were used in 2007.
‡Infection rate is in units of 1,000 mosquitoes and determined by maximum-likelihood estimate. Infection rate was 0 for all collection dates in 2006.
§Vector index is the product of light trap index and infection rate. Unit of measure is number of infected female Cx. tarsalis mosquitoes per trap night. Vector index values were 0 for all collection weeks in 2006.

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