(CNN) -- Despite a 35% jump in West Nile virus cases since last week, federal health officials said Wednesday that they believe the worst part of the U.S. outbreak is past and expect the number of cases to decline.
"We think the worst part of the epidemic is behind us," said Dr. Lyle Petersen, director of the U.S. Centers for Disease Control and Prevention's Division of Vector-Borne Diseases.
Unless next week's number of cases shows a surprising increase, he said, Wednesday's briefing will be the final one for the 2012 West Nile virus season.
As of Tuesday, 2,636 cases of West Nile virus had been reported to the CDC this year, including 118 deaths, officials said. Last week, the CDC reported 1,993 total cases of West Nile virus and 87 deaths.
The cases are the highest number reported to the CDC through the second week of September since 2003, Petersen said.
Health officials have said in previous weeks that the case numbers were the highest since 1999, when the virus was first detected in the United States.
Petersen noted that a reporting anomaly that occurred in 2003 changed this week's results. However, he said, this year's outbreak has proved to be the most serious since 1999, because of a high number of cases triggering neuroinvasive illnesses like encephalitis or meningitis.
While all the lower 48 U.S. states have reported cases of West Nile, six states have been responsible for two-thirds of the cases reported this year: Texas, South Dakota, Mississippi, Michigan, Oklahoma, and Louisiana.
Texas has the majority of infections, accounting for nearly 40% of West Nile virus cases reported in the past week. Alaska and Hawaii have remained untouched by the virus.
The CDC continues to work with health officials in Louisiana and Mississippi in the aftermath of Hurricane Isaac, Petersen said, adding that neither state has seen a large increase in cases after the storm, something health officials had predicted.
Petersen again emphasized Wednesday that prevention and protection are the best defenses for fighting mosquitoes carrying the West Nile virus.
Mosquito breeding areas can be prevented by removing standing water from outdoor containers and objects that collect standing water. He also urged that residents support local mosquito control programs that prevent infestations by the pests.
Protect against mosquitoes by wearing long pants and sleeves during the prime mosquito moments of dusk and dawn. Make a habit of applying insect repellent if you are spending time outdoors, and fight indoor mosquitoes by using air conditioning, and repairing screens on doors and windows.