Tarrant County public health officials on Friday defended their reporting of West Nile cases, dismissing a Dallas County analysis that suggested local officials might have undercounted the number of severe cases during this year's outbreak.
Officials with the Dallas County Health and Human Services Department used a federal formula and blood donor data from Carter BloodCare, the largest blood bank in North Texas, to estimate how many people in Dallas, Tarrant, Denton and Collin counties were likely to have contracted the neuroinvasive form of the virus.The neuroinvasive form is the most severe. It can attack the brain and nervous system, paralyze the body and leave life-changing impairments.The Dallas County analysis estimated that Tarrant, which had the most West Nile-infected blood donors in the state, should have as many as 280 neuroinvasive cases. Tarrant officials had confirmed 96."I think the important thing to say is that it's an estimate and that estimate is just wrong," Sandra Parker, Tarrant County Public Health's medical director, told the Star-Telegram. "What we really should be focused on is the actual case count."Parker said Tarrant County's reported neuroinvasive cases were based on lab reporting, hospitalizations and the number of West Nile test kits that were used this summer.After talking with Dallas County officials, Parker said Tarrant believes that the calculations were incorrect and that there is no evidence that the severe cases were underreported.Dallas County's findings were reported Wednesday by The Dallas Morning News in a story that was also published in the Star-Telegram.Wendy Chung, chief epidemiologist for Dallas County, said no conclusions were intended to be drawn from what she characterized as "a preliminary analysis.""These are not hard and fast numbers," said Chung, who said her office had heard Tarrant County's concerns but believe that they applied the formula correctly. "If you found a better way to calculate that, that's wonderful."She said blood donor data was a critical tool in alerting authorities to the seriousness of the outbreak in early July when the number of infections started to soar. And she believes the federal Centers for Disease Control will be studying the North Texas outbreak, trying to learn more about West Nile."There is a wealth of information to be learned for years to come," Chung said. "Why was it so severe? Why here? Why now?"State health officials said they have no data to suggest that the most serious cases were underreported in Tarrant County."I don't believe there were neuroinvasive cases that were missed," said Chris Van Deusen, a spokesman for the Texas Department of State Health Services.While less serious cases often go unreported because people never have symptoms and don't seek medical help, Van Deusen said the state believes it has a good handle of the number of neuroinvasive cases."All the evidence shows pretty high reporting on that because it tends to be so serious," Van Deusen said. "Additionally, we're pretty confident that doctors and clinicians were aware of West Nile and actively diagnosing it."A report published in the April 2012 edition of Emerging Infectious Diseases, which looked at plasma from blood donations in North Dakota from November through December 2008, found that for every 256 to 353 West Nile infections reported there would be one neuroinvasive case. But the study cautioned that West Nile "varies markedly" by age and sex, making it difficult to come up with a formula that takes those factors into account."I'm not saying we have problems with estimates in general," Parker said. "But you still have to use the correct variable for your calculation to be correct."The neuroinvasive cases reported by Tarrant County are consistent with the numbers of tests run by state health officials and the number of hospitalizations for neuroinvasive West Nile infections, Parker said."What's important to remember is that this is a model that gives an estimate and it has to be recognized as such," she said."Some of the data might be useful in planning and might be used in future years. But it is a model."Staff writer Mitch Mitchell contributed to this report.Bill Hanna, 817-390-7698Twitter: @fwhannaHave more to add? News tip? Tell us
