CHARLESTON, W.Va. -- A month after completing their work in West Virginia, federal scientists are still working to finalize an analysis of hospital records of residents who were treated after last month's Elk River chemical leak, and are planning additional work to help understand the leak's public health impact.U.S. Centers for Disease Control and Prevention officials are conducting a patient-chart review, which will give more detail about how many residents exposed to contaminated water sought hospital treatment and what types of symptoms they experienced.The report is not necessarily designed to provide any concrete answers about whether chemical exposure caused those symptoms, or address claims by some state officials that such symptoms were really related to the flu or anxiety about the chemical leak. However, with a more definitive examination of the population's potential chemical exposure and reported symptoms, scientists will be better able to understand the leak's effects on public health."Generally speaking, the scientists would be looking for patterns and associations, and sometimes suggestions for follow-up," said CDC spokeswoman Barbara Reynolds. "The cause would not be captured in the data collected in this Epi-Aid."The phrase "Epi-Aid" is the CDC's term for epidemiological assistance the agency provides to states. Epidemiology is the study of patterns, causes and effects of health problems in defined populations.In this instance, the CDC is responding to a state request that federal scientists help to assess the impact of the leak of the coal-cleaning chemical Crude MCHM from the Freedom Industries tank farm. The leak, just upstream from West Virginia American Water's intake, contaminated the water supply of 300,000 people in nine counties.Loretta Haddy, state epidemiologist with the Bureau for Public Health, said Thursday the CDC's report is based on the agency's review of hospital records of the more than 500 people who sought treatment after the leak.The report will provide what Haddy called "descriptive epidemiology," meaning it will outline what sorts of symptoms patients experienced and what sorts of chemical exposures they might have reported to doctors. Some of that information has been made public before, in periodic state briefings and interviews with local health officials. The CDC's analysis of the hospital charts is much more methodical, officials said."It's a little more descriptive," Haddy said of the CDC report.Haddy said the CDC analysis would "look closely for associations of cause, but one of the limitations is that you cannot have direct association of cause" based only on the hospital record review.Five days after the leak, Haddy wrote to the CDC and its sister agency, the Agency for Toxic Substances and Disease Registry, to request assistance in performing what's called an Assessment of Chemical Exposure, or ACE, to help understand the leak's impacts.Among other things, Haddy asked for the hospital chart review and a broader study called a Community Assessment for Public Health, or CASPER.Haddy said Thursday that this project, scheduled to start in early April, would involve a door-to-door survey of more than 200 homes in the region. Residents would be asked a variety of questions about the leak, including if they were exposed to the water and if they experienced any health problems.While the hospital chart review provides information about residents who sought medical treatment, the door-to-door survey will give scientists information about a more random selection of residents, Haddy said.In the days just after the chemical leak, the CDC repeatedly dodged questions about how it developed a Crude MCHM screening level that state officials and the water company used as a target concentration for lifting the broad "do-not-use" order that was issued.Since then, after the Tomblin administration came under heavy criticism for its response to the water crisis, state officials briefly began pointing fingers at the CDC and the U.S. Environmental Protection Agency, saying federal officials had not provided the state with enough help.Such comments have re-emerged in recent days. For example, a state-hired water and plumbing system expert, University of South Alabama engineer Andrew Whelton, publicly asked why the CDC's report on health impact hasn't been released yet.On Thursday, all five members of the state's congressional delegation wrote to CDC Director Thomas Frieden to support a Feb. 18 request from Gov. Earl Ray Tomblin for federal help."This disaster has been ongoing for over a month now," the congressional delegation's letter stated. "There is palpable concern and frustration among our citizens, which we share. It is clear that additional testing is necessary to protect the health and safety of West Virginians, and to reassure the public."It's not exactly clear, though, what specific studies Tomblin was asking the CDC to perform. The governor's letter mentions, "Further epidemiological and/or toxicological studies," as well as "a specific need to address ongoing population surveillance or monitoring."Amy Goodwin, Tomblin's communications director, said the administration wants the CDC to provide guidance on short- and long-term monitoring of exposed residents and to provide money for such studies.Reynolds, the CDC spokeswoman, said the agency does not do the sort of toxicological testing that would expose lab animals to Crude MCHM to develop more data about the chemical's health impact. Reynolds said the CDC has not yet responded to the governor's letter, but would do so.Haddy said her agency is awaiting results of the CDC's hospital chart study, which is undergoing internal review and should be released soon.Under various versions of CDC guidelines -- all dated from the 1990s -- the chart review report was supposed to have been completed within 14 days of CDC officials returning to their offices from their field work in West Virginia. The CDC team was in West Virginia from Jan. 16 through Jan. 30, Reynolds said.CDC officials said the agency guidelines for Epi-Aid reviews have not been updated and "may be outdated in practice."The agency's "optimal goal" for such a report to be completed is to have a draft within two weeks for internal review, Reynolds said.Reach Ken Ward Jr. at firstname.lastname@example.org or 304-348-1702.