Surveillance and alert levels

319 dead birds reported
37 tested
0 positive for WNV

2 tested
0 positive for WNV

Winter season; little or no mosquito activity.

No West Nile virus positive birds or mosquitoes and no cases in horses or people in King County in the current calendar year.

Areas of King County with limited West Nile virus activity in birds and/or mosquitoes but no positives prior to August 1.

First West Nile virus positive birds or mosquitoes found before August 1

OR a confirmed horse or human case

OR sustained West Nile virusactivity in birds or mosquitoes in the absence of horse or human cases.

High risk of human outbreak

• high dead bird densities starting in early summer;
• sustained high mosquito infection rates;
• multiple positive mosquito species;
• increasing number of infected horses or other mammals;
• a human case with high levels of bird, mosquito or horse infections;
• areas with early West Nile virus activity that experienced epidemic conditions in past years.

Multiple confirmed human cases with conditions favoring continued transmission to people (e.g., persistent high infection rates in mosquitoes, continued bird deaths due to West Nile virus)