While investigators have not yet pinpointed the exact ingredient causing the outbreak, they are focusing on slivered onions and beef patties -- both of which have been removed from restaurants in the affected states pending further investigation.

Quarter Pounder hamburgers in some states may be temporarily unavailable, added the CDC.

The agency advised those who consumed a Quarter Pounder and developed symptoms of E. coli poisoning -- such as diarrhea, a fever over 102 degrees Fahrenheit (38.9°C), and vomiting -- to seek medical attention. 

Symptoms typically begin three to four days after exposure, and most individuals recover within five to seven days without treatment. However, some cases can become severe and require hospitalization.

McDonald's did not immediately respond to a request for comment.