Numbers paint confusing picture of West Nile outbreak

Aerial spraying. Instant updates via live blogs. Nightly reports on the local news. Even a mention on the Al Jazeera network.

The West Nile virus' charge through North Texas has been analyzed, reported on and speculated about from every angle. It has gone national, and even global. But how does the local outbreak compare with other parts of the state and nation, and with past incidents?

It's not exactly clear.

A Star-Telegram examination into the available data found inaccuracies in the state's calculations of West Nile deaths and a considerable lag in numbers reported by the federal Centers for Disease Control and Prevention in Atlanta.

Even as Dallas and Tarrant counties report a record number of West Nile cases, prompting controversial aerial and ground spraying of pesticides, the available data makes understanding the scope of the problem extremely tricky, if not impossible.

One veteran Texas epidemiologist who studies West Nile said the lack of reliable data doesn't change the fact that Texas and other states are dealing with an outbreak.

"We're looking at something that hasn't happened in all the years since" the virus was found, said Dr. Victor Cardenas, an epidemiology professor at the University of Texas School of Public Health.

"It's a horrible disease," he said, noting that people with high blood pressure and kidney problems are susceptible to the more severe effects. "I've interviewed people (who) one or two years later are still recovering. It's debilitating."

This year, there have been more than three dozen fatalities in 32 states, most of them in Texas.

Tarrant County has reported 212 cases of West Nile, far more than the 183 total reported in the nine years previous, from 2002-11. The county's four deaths are the most since seven people died in 2006.

But putting the numbers into context has proved difficult.

Confusion by the numbers

The Star-Telegram found a number of discrepancies in state and federal reporting on the virus:

-- The state reports 586 cases of West Nile virus and says 340 of those are in Dallas and Tarrant counties. The CDC's numbers are 336 statewide and 198 locally. Local health department officials, however, count 474 cases in Dallas and Tarrant counties as of Tuesday.

-- The federal government is lagging behind other entities and thus is underreporting fatalities by about 70 percent. The CDC said there had been 26 deaths as of Aug. 14. The Star-Telegram found at least 45, including Tuesday's confirmation of an 11th death in Dallas County and the first reported death in Collin County.

-- In Texas, the CDC reports 14 deaths. In Tarrant, Dallas, Denton and Travis counties alone, officials have reported 17, with at least eight more in other counties.

-- The state health department's historical data for West Nile cases and deaths is off by at least 14 percent. From 2002 to 2011 the department's website listed 1,331 cases -- the Star-Telegram found 1,521 -- and 122 deaths; the actual count was 140.

A health department spokeswoman said the numbers would be changed after the Star-Telegram asked about them.

The experts say there are plenty of reasons for the differences.

Carrie Williams, spokeswoman for the Texas Department of State Health Services, said case information travels from local health officials to the state, then to the federal government.

Physicians report suspected cases to the regional or local health department within a week of diagnosis, she said. Local officials investigate factors such as dates of onset and results of lab work and may announce the number of cases they are investigating or have just completed.

"Their numbers are always larger because the case file has not yet been received and validated by the state," Williams said.

In Tarrant, cases of West Nile are reported to Tarrant County Public Health by the medical community. Reporting entities use private and state labs to confirm a case, said spokeswoman Vanassa Joseph.Local officials then turn over the information to the state, which takes a few days to validate it, Williams said.

"We carefully review and analyze the form to determine if the patient's symptoms and test results meet the" definition for reporting purposes, she said. Confirmed cases are then reported to the CDC.

The state notes that local health departments report cases of West Nile virus and may have more up-to-date numbers on new cases in their areas. The state's numbers, however, were most recently updated Monday.

Cardenas said other factors may be in play, including the residency of a patient, who may be treated in one county but live in another.

"The nature of surveillance (of disease) is, the data that they put out is preliminary," he said.

Kelly Craine, a spokeswoman for the Waco-McLennan County Public Health District, said that although accuracy is important, numbers aren't everything. (The state reports the county has 12 West Nile cases, while it actually has 21.)

Even if a nearby county has a spike in cases, health departments focus more on how the county is dealing with the problem and whether cases were in a cluster or widespread.

The "response is more important than the numbers," she said.

Darren Barbee, 817-390-7126

Twitter: @DarrenBarbee

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