Syphilis cases rise among unhoused drug users at San Diego-Tijuana border as researchers face NIH limits and penicillin shortage

Researchers at the University of California San Diego have been working for years to build trust with unhoused people who use drugs on both sides of the San Diego‑Tijuana border. Their outreach has uncovered that roughly ten percent of participants screened since spring are currently infected with syphilis, a rate that could have gone unnoticed without the program.

The team’s community‑based testing has helped identify infections that might otherwise remain untreated, offering a chance for early medical care. However, the effort is now hampered by new federal rules that restrict collaborations with foreign institutions, limiting the ability to share data and coordinate treatment across the border.

Compounding the problem, a nationwide shortage of intramuscular penicillin – the standard therapy for syphilis – makes it uncertain whether all diagnosed patients can receive the full course of treatment. The combination of regulatory constraints and drug scarcity threatens to undermine progress in controlling the outbreak in this vulnerable population.