A brand of penicillin used to treat pregnant women infected with or exposed to syphilis is in short supply across Los Angeles County and nationwide, and physicians were urged Thursday to maintain reserves.

Called Bicillin L-A, the drug is made by Pfizer, which has reported a manufacturing delay of the product, Los Angeles County Public Health officials said in an alert.

Officials with the federal Centers for Disease Control and Prevention issued a similar alert late last month, urging physicians to refrain from using the drug on individuals with other sexually transmitted diseases. Although the Food and Drug Administration told medical experts the shortage should be resolved by July, the delay is concerning to local health officials.

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The drug is the only one recommended for pregnant women with syphilis.

“This is of particular concern in Los Angeles County because we are experiencing a significant increase in syphilis, as are many parts of California, including syphilis among pregnant women and congenital syphilis among infants,” the L.A. County health department said in a statement.

Congenital syphilis occurs when the disease is transmitted from an infected mother to her child during pregnancy.

This brand of penicillin used to treat syphilis in pregnancy is “nearly 100 percent effective at preventing the potentially devastating outcomes associated with congenital syphilis,” according to the county alert.

Officials with California’s public health department have said an increasing number of women statewide are contracting the disease and passing it on to their newborns.

From 2012 to 2014, the annual number of reported syphilis cases among women more than doubled from 248 cases to 594, according to the California Department of Public Health.

But health officials said what’s more alarming is the number of reported congenital syphilis cases, which tripled during the same period, from 30 to 100.

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Pregnant women with untreated syphilis can potentially deliver a low-birth-weight baby who will endure many health problems, according to the CDC. A baby may also be born too early or stillborn. The number of stillborn cases in California among pregnant women with untreated syphilis rose from one case in 2012 to six cases in 2014.

Most of the cases among women have been reported in the Central Valley and Los Angeles County, according to state health officials.

In Los Angeles, there were 31 probable cases of syphilis among babies born in 2014 compared to six in 2012.

Syphilis is a sexually transmitted disease that is easily treated. Symptoms include sores at an early stage or a rash at a later stage.