Figure. Rates of flavivirus seroconversion in sentinel chickens, Florida, 1988–2007. Black shading shows St. Louis encephalitis virus (SLEV); white shading shows West Nile virus (WNV). Because the number of susceptible sentinel chickens fluctuated during this time, the rates of seroconversion (no. positive chickens/total no. susceptible chickens × 100, per month) are presented rather than numbers of positive birds. SLEV seroconversion rates declined after the 2001 introduction of WNV despite continued surveillance, and an increased number, of susceptible birds located in regions historically at risk for SLEV enzootic transmission.