The first ever case of superbug in the US was reported on Thursday. A rare type of E. coli superbug was found inside a Pennsylvania woman last month.

The 49-year-old woman showed symptoms of infection in the urinary tract after Walter Reed National Military Medical Center tested the sample. However, it does not seem to scourge widely, according to CNN.

The superbug found in the woman is treatable. However, researchers are concerned that the drug-resistant gene mcr-1 could spread heavily to other bacteria. It takes place on the plasmid, and then spreads to other species of bacteria.

“The discovery of this gene in the U.S. is equally concerning, and continued surveillance to identify reservoirs of this gene within the military healthcare community and beyond is critical to prevent its spread,” Dr. Patrick McGann of the Multidrug-Resistant Organism Repository and Surveillance Network (MRSN) at the Walter Reed Army Institute of Research (WRAIR) said in a report by Fox News.

Colistin, an antibiotic, is the only hope when no other antibiotics work. However, it is resistant to Escherichia coli strain SHP45. If it spreads, it can resist all antibiotics.

“Colistin is one of the last efficacious antibiotics for the treatment of highly resistant bacteria. The emergence of a transferable gene that confers resistance to this vital antibiotic is extremely disturbing,” said McGann.

The Pennsylvania State Health Department and the Centers for Disease Control and Prevention are investigating the woman’s contacts to check if the bacteria had spread to other places.

Moreover, CDC is checking the health clinic she visited for the test.

Last year, the World Health Organization published a fact sheet that stated that antibiotic resistance is also rising due to the misuse and overuse of antibiotics.

“A growing list of infections—such as pneumonia, tuberculosis, blood poisoning and gonorrhoea—are becoming harder, and sometimes impossible, to treat as antibiotics become less effective,” reported the WHO.