NEW ORLEANS - Big West Nile numbers in the far West got most of the attention this year, but it appears to be a more persistent problem in the South - especially along the Gulf of Mexico.
All five Gulf Coast states were among the top 15 for serious cases, even though the number of such cases either fell or stayed about the same as last year's. Four other Southern states were in the top 20.
"I wonder if we're seeing the emergence of more of a steady-state pattern, where we're going to see these numbers almost every year in these areas," said Roy Campbell, an epidemiologist with the Centers for Disease Control and Prevention.
Texas, Louisiana and Mississippi - No. 20 last year - all were in the top six this year for neuroinvasive disease: encephalitis and meningitis, which can kill or cause brain damage.
In more central states, there will sometimes be huge outbreaks along rivers or lakes, said Dr. Raoult Ratard, Louisiana's state epidemiologist. "But consistently, year after year, probably the Gulf Coast will have more regular concentrations," he said.
Mosquitoes thrive along the area's many waterways, but they do that just about anywhere.
But the South's warm winters mean a longer mosquito season, and more birds for them to bite - both those which stay year-round and those which come South for the winter.
"I think it's becoming an endemic disease in these areas," Campbell said. "You could compare it to something like malaria, that used to be endemic in those areas a hundred years ago and then disappeared.
"But malaria is more or less steady state. Your risk is more or less the same each year, and case numbers are about the same each year."
As the West Nile epidemic spread westward, many states have had one year with many cases, followed by almost none the next year. Half the states in last year's top 10 for encephalitis or meningitis caused by the virus aren't even in this year's top 20.
Last year, Texas was No. 2 and Louisiana was No. 6. The number of neuroinvasive cases in Texas dropped more than three-quarters, from 431 to 98 as of Nov. 30. But that was still the nation's third-highest number of such cases.
Louisiana, which had 101 serious cases last year, had reported 68 to the CDC by Nov. 3, making it No. 4.
Mississippi, No. 20 last year with 34 cases, had 31 this year, putting it sixth in the country. Florida's caseload fell from 61 to 29, but its ranking rose from 14th to eighth. Alabama, although the number of people with neuroinvasive disease fell from 25 to 15, went from 23rd to 13th.
In the meantime, Colorado, which had 621 serious cases last year, had 39 through November, moving from the largest number to the sixth-highest. Nebraska went from 194 cases to four - third-highest to 29th. South Dakota went from 151 cases to six; No. 4 to No. 25. Pennsylvania, which had the fifth-largest number in 2003, was No. 22 this year as the numbers fell from 145 to nine.
Last year was the first that the CDC separated its data into neuroinvasive disease and West Nile fever, which is less serious.
Louisiana did that earlier. In 2002, the worst year for the state, it had at least 204 cases of meningitis and encephalitis and 19 deaths among 329 West Nile infections.
"The first season, we had several waves," Ratard said. One around Lake Pontchartrain was followed by other clusters of cases in Lake Charles, Monroe, and Alexandria.
Last year, Shreveport was the only area with a major outbreak; other cases were dotted around the state. "That was kind of interesting, because Shreveport was kind of spared the first year," Ratard said.
Shreveport had another group of cases this year, as did Baton Rouge. Otherwise, again the cases were sporadic and without pattern.
"So two years in a row we have a focus in Shreveport, and Baton Rouge is back after one year that was fairly calm," Ratard said.
"I think the pattern we are going to see is sporadic cases throughout the state, maybe 20 to 30 cases. And on top of that, if there is a particular city or one or two parishes where the circumstances (for an outbreak) are met, then an intense focus of transmission.
"How do we predict these intense foci? We don't know yet."
One thing scientists do know: Even though a million people have probably been infected, that's a tiny percentage of the U.S. population.
"So most people are susceptible. Only a few percentage of people have been infected silently and therefore have immunity to it," Campbell said.
That means the rest can still get it.
"Those people shouldn't let their guard down in mosquito season," Campbell said.