The news comes after a labeling issue was to blame for the accidental release of a coronavirus patient who was on her way back to Marine Corps Air Station Miramar in San Diego to join other quarantined evacuees when officials found out her test was positive.
"[We] can and should be prepared for this new virus to take a foothold in the U.S.", where there have been 14 confirmed cases so far, she told reporters.
Since late January, the agency has rushed to distribute the kits to allow states to conduct their own, faster testing rather than ship all samples to its headquarters in Atlanta.
"Things may not always go as smoothly as we may like", Dr. Messonnier said.
The C.D.C. announced last week that it had begun shipping about 200 kits to laboratories in the United States and roughly 200 more to labs in other countries.
Some of the kits, which also were sent to at least 30 countries, produced "inconclusive" results because of flawed components - and the CDC said it planned to send replacements to make them work.
It was not immediately clear how many kits were flawed.
Nancy Messonnier, MD, who directs the CDC's National Center for Immunization and Respiratory Diseases, said the CDC developed and deployed the diagnostic test kits to states, and as part of the normal process, state labs verify that they perform the same as they do in CDC labs before states use them to diagnose patients.
So far, there have been just two known cases of human-to-human transmission in the United States but, after hopeful signs the outbreak might be subsiding, China Thursday reported a huge surge of more than 14,000 new cases.
The agency is now re-evaluating the test kits and working with state labs to correct problems, Messonnier said.
"It's concerning that there is a high number of cases", she said.
"At the time, they were relying on phone conversations to relay test results and the CDC in Atlanta told officials in San Diego that all tests were negative", a CDC representative said on Tuesday.
The new numbers will likely change health officials' approaches.
The patient is now in isolation at a California hospital and, to date, has only mild disease, Messonnier said.
"The mishap was unfortunate but we have corrected this from happening again in the future by adding additional quality control", Messonnier added.
Although he noted during a press briefing that the number of cases of COVID-19 in China, epicenter of the outbreak, appears to be stabilizing, "we're not going to talk about numbers or dates".
If the end of the outbreak is in the offing, Messonnier said it was likely down to the "aggressive actions" - including travel restrictions and quarantines - taken by China, the United States and other affected countries. That patient is one of 13 now known to be infected with the new coronavirus in the U.S.
"We are seeing fewer and fewer travelers because of travel restrictions" implemented here and in China, Messonnier said.
Still, the agency is asking all travelers arriving from mainland China to effectively place themselves in quarantine at home - and limit outside activities - for a minimum of 14 days, while monitoring for symptoms of the virus.