Infectious disease experts are warning that a shortage of a key antibiotic for treating the sexually transmitted infection syphilis could make it hard to fight the spread of the disease.

The United States already has a big problem with syphilis, with cases rising for more than 20 years. Cases increased nearly 75% between 2017 and 2021 alone, bringing the number to more than 176,000 in 2021, according to the U.S. Centers for Disease Control and Prevention.

Meanwhile, drugmaker Pfizer recently announced the shortage of its Bicillin L-A, also known as penicillin G benzathine, which could continue into next year.

Reasons for scarcity of the long-acting injectable antibiotic include increasing demand because of the rising number of syphilis infections. The medication can also be used in place of amoxicillin to treat infections like strep throat and amoxicillin has also been scarce recently, the New York Times reported.

Among the concerns is congenital syphilis, which has a high fatality rate and can also lead to severe birth defects, the Times reported. Bicillin is the only recommended treatment for infected pregnant women.

"It worries me that these moms may not have access to lifesaving medication," Dr. Anita Henderson, a pediatrician in Hattiesburg, Miss., told the Times.

Alternatives for pregnant women are years away from becoming available, Dr. Jeffrey Klausner, an infectious disease expert at the University of Southern California, told the Times.

Pfizer spokesman Steven Danehy told the Times it will likely take a year to increase production by 50%.

The CDC is recommending that doctors give preference for the medication to pregnant patients and infected or exposed infants. Others should be prescribed doxycycline for two to four weeks.

The shortage is part of a widespread drug shortage crisis that has led to rationing of chemotherapy treatments, among others.