As of Tuesday, deaths were up 32 percent compared to the previous week. The total now stands at 87 since the beginning of the year, the CDC said.
Total cases including the deaths from the mosquito-borne disease stood at 1,993, a rise of 25 percent since August 30.
The numbers are the highest recorded through the first week of September since the virus was first detected in the United States in 1999, the Atlanta-based CDC said.
While virtually the entire country has been affected by the outbreak, 70 percent of cases are concentrated in six states — Texas, Mississippi, Louisiana, Oklahoma, Michigan and South Dakota.
The record number of cases registered in 2012 could be due to a relatively mild winter, an early spring and hot summer, according to the CDC.
Other factors potentially contributing to the outbreak are birds transporting the virus — first identified in Uganda in 1937 — and the exploding mosquito population.
About one in 150 people infected will develop severe illness with symptoms that include high fever, convulsions, vision loss, numbness, coma and can cause permanent paralysis and neurological damage.