The flu strain is resistant to the commonly used anti-flu drug, Tamiflu, but has successfully responded to other treatments, the Chicago Tribune reported Saturday.

"If you had two viruses in the same cell, they could recombine and generate a new virus. The fact that we're seeing resistance to first-line medications is worrisome," said Steven Wolinsky, chief of infectious diseases at Northwestern University.

The Illinois Department of Public Health reportedly warned medical professionals Thursday that intensive care flu patients should be given a combination of treatments until experts analyze the virus they have.

A solitary Chicago health facility was responsible for eight of the drug-resistant flu infections, officials said.

This season, 4.6 percent of flu test samples reportedly have shown evidence of resistance to drugs.