The Centers for Disease Control and Prevention says a glitch in its bird flu test hasn’t harmed the agency’s outbreak response. But it has ignited scrutiny of its go-it-alone approach in testing for emerging pathogens. The agency has quietly worked since April to resolve a nagging issue with the test it developed, even as the virus swept through dairy farms and chicken houses across the country and infected at least 13 farmworkers this year. At a congressional hearing July 23, Rep. Brett Guthrie (R-Ky.) asked about the issue. “Boy, that rings of 2020,” he said, referring to when the nation was…