The West Nile virus outbreak that has infected people in 38 states is on track to be the worst in history, a top official at the U.S. Centers for Disease Control and Prevention told a news teleconference today.
The CDC has recorded 1,118 infected people with 41 deaths, but health officials say they expect reported cases to rise dramatically. The disease generally peaks in mid-August, and the new infections generally take a couple of weeks to show up in the tally.
"Thus, we expect many more cases to occur," said Dr. Lyle R. Petersen, director of the Division of Vector-Borne Infectious Diseases at the CDC.
Petersen said the number of people infected has risen substantially in the past few weeks. Just one month ago, a mere 29 cases had been detected. As of Tuesday, he said, 47 states had reported indications of the virus in humans or animals; only Alaska, Hawaii and Vermont have so far been spared. Human cases have been detected in 38 states.
The total, he said, is the highest number of West Nile virus cases reported to the CDC by this time in the summer since the disease was first detected in the United States in 1999. In short, this outbreak is on track to be the worst in the country's history.
The worst year on record is 2003, in which the country saw 9,862 cases of West Nile virus infection and 264 deaths.
He described more than half of these cases -- 56 percent -- as neuroinvasive, meaning the infection had spread to the brain in these patients.
While it is unclear why this year has been harder hit than others, many think it is possibly because of the weather.
"It is a very complicated ecological cycle," Petersen said. "Hot weather, we know from experiments in the laboratory, can increase the transmission of the virus."
It is possible that the mild winter and the hot summer also increase the number of mosquitoes, which spread the virus.
The health departments and blood banks are also making efforts to protect the blood supply. To date, the virus has been detected in the blood of 242 donors. Donated blood is routinely screened for West Nile virus.
Seventy-five percent of the cases have been reported from five states: Texas, Mississippi, Louisiana, Oklahoma and Illinois. Texas appears to be the hardest hit, with 586 reported cases in total. The death toll so far in Texas is 21, but it appears that at least four additional deaths will soon be added to the total. Dallas County has been hardest hit, with a total of 270 cases and 11 deaths.
"We are talking about hundreds, if not thousands, of people whose lives will be changed," said Dr. David L. Lakey, commissioner of the Texas Department of State Health Services. "Texas has really been the center of this outbreak."
The totals are creeping closer to the 2003 figures in Texas, which were the worst ever for the state. In that year, Texas recorded 438 cases and 40 deaths statewide.
There are several components to the Texas government's response. It has been coordinating with local health departments to obtain as much data as possible and track the areas hardest hit. Additionally, a new lab test to detect the virus has been implemented, allowing doctors to get an answer in two days while previous tests took 10.
Initially, they were using ground sprays to kill the mosquitoes harboring the virus, but aerial spraying has since been added to the strategy. "It would have been impossible for us to cover the county with land-based spray," Lakey said.
To prevent spread of the disease, the CDC encourages the public to use insect repellent, wear long sleeves, replace or repair screens on windows and doors, empty standing water and to support local mosquito control.