According to CDC spokesperson Tom Skinner, the agency actively sought to contact Speaker and prevent him from traveling even before they believed he carried the XDR strain.
But he added that learning that Speaker may have been carrying the more deadly strain, increased the level of concern.
"Certainly, news that [we might be] dealing with XDR added a level of seriousness," Skinner said. "The fact that he had XDR ratcheted up the seriousness of our response."
He added, though, that the agency's response to the situation would have been no different in either case.
"The public health measures were in place prior to us being informed that it was XDR TB," Skinner said. "We may have been talking of mutant bacterial strain that we picked up. If they don't find it, it doesn't change the fact that there was XDR TB there."
Skinner said Speaker originally learned from health officials that he carried the MDR strain of the disease on May 10 and was urged at the time not to travel. The CDC took action on the case on May 18, Skinner said, and they contacted him by phone on May 22.
By this time, Speaker was in Rome, and CDC officials instructed him to turn himself in to Italian health authorities, Skinner said.
Instead, Speaker boarded another trans-Atlantic flight to Canada before entering the country through a checkpoint in Champlain, N.Y.
Now, National Jewish Medical Center is testing the original culture examined by the CDC in March — the sample that the CDC used in their determination that Speaker's tuberculosis was the XDR version.
The results of this test will be available in about two weeks, said Daly. But the effort is stymied somewhat by the fact that, according to laboratory protocol, the original sample from which the culture was grown, was thrown away.
The new finding could have major implications for Speaker's prognosis; while XDR survival rates normally hover between 30 and 40 percent, those of MDR are around 70 percent.
But the fact remains that Speaker still requires significant medical attention.
"MDR bacteria remains difficult to treat," Cohen said, adding that those with the infection face two years of aggressive antibiotic therapies known for significant side effects.
The change from XDR to MDR also does not change Speaker's status at National Jewish Medical Center; he is still under order by Denver public health officials to remain at the hospital in isolation.
And disease experts say that it is still possible that both tests were actually accurate — that is, Speaker may have been infected with both the MDR and XDR strains.
"If that was a mutant that was there then, I don't know where it is now," Daly said. "We always base our clinical decisions on the predominant organism, which right now is MDR TB."
Cohen concurred. "In this patient, the predominant strain appears to be MDR tuberculosis."
In addition to changing Speaker's prognosis, it is possible that the diagnosis discrepancy could have implications other than those related to health.
"This saga is far from over, at least legally," said ABC News medical editor Dr. Timothy Johnson.
The difference in results also reveals the need for better testing methods.
"Misdiagnosis of XDR is possible, in view of the difficulties in lab tests today to declare the presence of resistance to second line drugs," Raviglione said.
"The whole issue of testing for TB is often a gray area," Johnson said. "There is not automatically a black or white result."