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 s