PHOENIX, July 2 -- On a normal July 4th weekend, the main difference between a backyard barbecue and a West Nile virus exposure is whether the hosts remembered to empty the birdbath. This year, the Centers for Disease Control and Prevention would like everyone to remember the birdbath.

Data released by the CDC shows that as of June 30, 48 people in the United States had been confirmed with West Nile virus, 38 of them with neuroinvasive disease, the form of the infection that crosses into the central nervous system and can cause encephalitis, meningitis, or permanent paralysis. The historical average for confirmed cases by the close of June is roughly 10, measured since modern tracking began in 2004. The agency says this is the worst earl...