The national figures reflect a 40 percent increase in West Nile virus cases since last week.
Those stats indicate the number of cases may rival the record years of 2002 and 2003, the Associated Press reported.
Alameda County officials reported earlier this month that a .
In Contra Costa County, officials last week reported that two groups of mosquitoes from Brentwood and three chickens from Holland Tract in the Brentwood area had tested positive for West Nile virus.
The Centers for Disease Control reports 1,590 cases of West Nile virus in people, including 66 deaths, in 48 states. More than 70 percent of the cases have been reported from six states: Texas, South Dakota, Mississippi, Oklahoma, Louisiana and Michigan.
About 1 in 150 people infected with West Nile virus will develop severe illness, the Contra Costa Mosquito and Vector Control District reports.
Because symptoms can take two weeks to appear, reporting cases lags behind when people became infected. Typical symptoms are fever, headache and body aches.
The easiest way to avoid West Nile virus is to prevent mosquito bites and to take measures to limit mosquito breeding sites in standing water, government agencies say.
For more information, view this West Nile Virus fact sheet.