US lawmakers on Monday said they were expanding their investigation of federal biosecurity lapses including problems at the Centers for Disease Control and Prevention that led to the mishandling of anthrax and bird flu pathogens.

Republicans from the House Energy and Commerce Committee said they sent a letter on Monday to the CDC director, Dr. Thomas Frieden, asking him to explain why the leading U.S. public health agency was unable to detect systemic problems involving the handling of deadly agents dating back to 2010.

“Since part of CDC’s epidemiology work is detecting or recognizing patterns of disease outbreaks, how could CDC not recognize the pattern of select agent incidents?” five Republican lawmakers led by committee chairman Fred Upton of Michigan ask Frieden in the letter.

The lawmakers, who held a hearing with Frieden on July 16, also sent letters to the Food and Drug Administration (FDA), the National Institutes of Health (NIH) and the US Department of Health and Human Services Office of Inspector General.

The panel’s Oversight and Investigations subcommittee is investigating lapses including the potential exposure of more than 80 CDC employees to live anthrax bacteria in June and the unintended release of a deadly strain of avian flu earlier in the year.

FDA workers have also discovered vials of smallpox, dengue fever, influenza and other pathogens at a facility on the NIH campus outside Washington.

No one has fallen ill as a result of the incidents. But the committee is weighing the possibility of congressional action to protect against future dangers to public safety.