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Truvada was developed in the United States and first approved for use in H.I.V. prevention there in 2012. But the medication has been slow to gain a foothold in the country because of a variety of obstacles, including what Dr. Robert Grant, a professor of medicine at the University of California, San Francisco, called a “byzantine system” that many patients find impossible to navigate.

Some cities, including New York and San Francisco, have made strides toward providing free or subsidized access to PrEP, with corresponding declines in H.I.V. diagnoses. Gilead Sciences, the maker of Truvada, also recently promised to supply 200,000 uninsured patients with the pill.

And as of last month, most private health insurers are now required to offer the medication — which has a list price of about $2,100 per month — at no out-of-pocket cost to their policyholders.

But in poorer and more rural areas, patients and even doctors may not have heard of Truvada, said Dr. Grant, who led the development of PrEP. Costs for doctor’s appointments themselves might be prohibitive, or patients may be unaware of the assistance available to them, he said. In addition, Truvada has been stigmatized in some parts of the United States as promoting promiscuity, creating barriers to access and use.

Bill Bowtell, a strategic health policy consultant who helped lead Australia’s response to the AIDS crisis and continues to advise governments on H.I.V. policy, said the system in the United States “could not be set up better to maintain a continuing H.I.V. and AIDS pandemic.”



Rates of H.I.V. have remained largely unchanged in the United States in recent years: They continue to rise among gay and bisexual Hispanic and Latino men, and have not improved among gay and bisexual African-American men, according to figures from the Centers for Disease Control and Prevention.