CDC discovers pseudo-outbreak of whooping cough in Colorado

The U.S. Centers for Disease Control and Prevention has discovered that a cluster of suspected cases of whooping cough in Colorado was likely a "pseudo-outbreak," the result of contaminated test samples.

The cases were reported in the summer of 2009 and seem to have been mistakenly diagnosed due to test samples becoming contaminated at one medical clinic. The CDC also said that a cluster of whooping cough cases from the previous winter was likely a true outbreak, Reuters reports.

The Colorado outbreak was suspicious at the time because many patients did not have the classic whooping cough symptoms and many infections were in those who had been vaccinated. CDC teams swabbed the surfaces of the clinic that diagnosed the pertussis cases and found that 61 percent of the surfaces had pertussis DNA, which may have led to the contamination.

Sema Mandal, a lead researcher with the CDC, said that the pseudo-outbreak does not reduce the importance of the real cases of whooping cough that occur each year, including a cluster of 9,000 cases in California in 2010

"We've had strong evidence of other outbreaks," Mandal said, according to Reuters.

Whooping cough is a bacterial infection that causes severe, uncontrollable coughing. The disease infects between 30 and 50 million people and kills approximately 300,000 each year. While most children in the U.S. are immunized against whooping cough, there were still 27,550 reported cases and 27 deaths in the U.S. in 2010.

Other pertussis pseudo-outbreaks were reported between 2004 and 2006 in Massachusetts, New Hampshire and Tennessee.

Researchers, however, stress that whooping cough outbreaks are still a very real issue.

"Pertussis is a real problem, and we strongly recommend vaccination," Mandal said, according to Reuters.