The Centers for Disease Control and Prevention told staff it expects them to return to offices by Sept. 15, roughly five weeks after a gunman's deadly attack on the agency's headquarters in Atlanta, CNBC has learned.

"Your safety remains our top priority. We are taking necessary steps to restore our workplace and will return to regular on-site operations no later than Monday, September 15," Lynda Chapman, the agency's new chief operating officer , said in an email sent Thursday that was viewed by CNBC.

Chapman said all staff will be expected to return to their offices by that date, according to the email. For employees whose workspaces remain impacted by the shooting — including physical damage from the gunman's attack — the CDC will provide alternative spaces on its campus, Chapman

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