For decades, Uganda’s campaign against H.I.V. was exemplary, slashing the country’s death rate by nearly 90 percent from 1990 to 2019. Now a sweeping law enacted last year, the Anti-Homosexuality Act, threatens to renew the epidemic as L.G.B.T.Q. citizens are denied, or are too afraid to seek out, necessary medical care.

The law criminalizes consensual sex between same-sex adults. It also requires all citizens to report anyone suspected of such activity, a mandate that makes no exceptions for health care providers tending to patients.

Under the law, merely having same-sex relationships while living with H.I.V. can incur a charge of “aggravated homosexuality,” which is punishable by death.

Anyone who “knowingly promotes homosexuality” — by hiring or housing an L.G.B.T.Q. person, or by not reporting one to the police — faces up to 20 years in jail. Scores of Ugandans have been evicted from homes and fired from jobs, according to interviews with lawyers and activists.

Entrapment and blackmail — sometimes by the police — are rampant in person, on social media and on dating apps, according to interviews with dozens of people.

L.G.B.T.Q. people, and the advocates and health care workers helping them, have been subject to threats and violence.

The law has brought global condemnation and has dealt a significant blow to Uganda’s economy. But it is widely popular among its citizens. Many Ugandans see homosexuality as a Western influence and the law as a corrective. The country’s Constitutional Court is set to rule on the act’s legality as early as next week.

In response to pressure from global health organizations, the Ugandan health ministry in June guaranteed health care to anyone regardless of orientation or identity. It did not promise that patients would be safe from prosecution.

The country’s health ministry did not respond to multiple requests for comment on the act’s impact on public health.

But Dr. Jane Aceng, the health minister, has said on the social media site X that the government will ensure access to H.I.V. prevention programs and “remains committed to ending AIDS as a public health challenge.”

Others see a disaster in the making. Although the law targets L.G.B.T.Q. people, the resulting stigma and discrimination may deter all Ugandans from seeking health care, said William W. Popp, the United States ambassador to Uganda.

“Our position from the United States government is, the whole law should be repealed,” he said in an interview. “It’s a violation of basic human rights and puts all Ugandans at risk.”

Some shelters for people living with H.I.V. have closed, and some centers that once dispensed H.I.V. services on a walk-in basis now see clients for limited hours, often only by appointment, to minimize the chance of raids.

Dozens of health care providers and patients have been arrested.

“The government has tried very hard to create the impression that the Anti-Homosexuality Act is not really being enforced, that it is not an actual threat to L.G.B.T. people, but that’s not true,” said Justine Balya, a director at the Human Rights Awareness and Promotion Forum, which represents many of those arrested.

Uganda had been at the forefront of H.I.V. research and public health policy. The new law requires scientists to reveal the identities of study participants.

“It’s troubling from a research and academic perspective, and troubling from a scientific perspective to actually develop the medicines and tools we need to confront disease epidemics in the future,” Ambassador Popp said.

Worldwide, protection of gay rights is intricately linked to control of H.I.V.

Gay and bisexual men living in countries that enforce laws criminalizing homosexuality are 12 times as likely to be living with H.I.V. as those in the rest of the world, according to a recent U.N. report.

“We are suffering so much, and our life is in danger,” said Nathanian Issa Rwaguma, 34, a gay man and an activist.

Western supporters have offered few resources needed to protect L.G.B.T.Q. people, particularly those who have been outspoken, several said. “Do you expect a dead human-rights defender, or an alive one?” asked Hajjati Abdul Jamal, a 29-year-old transgender woman, referring to aid organizations.

Nearly all of those arrested are released after about a week, but a few could remain imprisoned for years awaiting trial, she added.

In March, three gay men and three transgender women who worked as H.I.V. educators were arrested in Jinja, a city in eastern Uganda.

They spent four months in prison enduring sexual harassment, beatings and two rounds of forced anal examinations, according to the doctor who runs the clinic where they worked and their lawyers. One educator was so severely lashed with a cane that she could not sit or lie down for two weeks.

In November, Mulindwa Benda, 24, a transgender man and educator, was in Busia, at the Uganda-Kenya border, to lead a workshop on sexual and reproductive health. He was charged with promoting homosexuality.

The police ridiculed him for “dressing like a man,” and held him for 72 hours in a tiny jail cell with eight women and a toilet that did not flush, Mr. Benda said in an interview.

Outreach workers in Lugazi, Mbarara and several other towns have been arrested for distributing lubricants and condoms. Police officers often associate the products with same-sex intimacy.

“It’s part of the overall climate of persecution and violence that strikes fear into health workers, as well as gay and bisexual men and trans women who need supportive, stigma-free H.I.V. services,” said Asia Russell, executive director of the advocacy group Health Gap.

About 13 percent of Ugandan men who have sex with men are living with H.I.V. Many are now cut off from care.

Mulago Hospital’s clinic for sexually transmitted diseases, among the largest in Kampala, used to treat more than 100 L.G.B.T.Q. patients a day. Now, fewer than half come into the clinic, said Dr. Afunye Anthony Arthur.

“The others hide out, so you have to look for them,” he said.

Dr. Afunye said he had been accosted by angry people at a restaurant and his home, where he lives with his wife and three young children.

To make visits safer for clients, Ark Wellness Hub, a clinic in Kampala, now stays open late into the evening and offers private appointments.

Although three of the clinic’s seven staff members have been evicted from their homes, “you have to find a way of going ahead with your work,” said Brian Aliganyira, its executive director.

Some clinics have resorted to stashing lubricants out of sight or using euphemisms to refer to them. At many clinics, staff and volunteers continue to provide care, spending their own money to deliver medications.

In an interview, a 32-year-old gay man said he had taught shoemaking but was forced to leave his job in July after he was accused of promoting homosexuality at the school. He was diagnosed with H.I.V. in 2021 and took his last anti-viral pill on Dec. 6.

Two of his friends died in August of H.I.V.-related complications after discontinuing treatment. But he was still too afraid to go to a clinic: Another friend was stoned to death in his village in Masaka district, he said, after an acquaintance recognized him on public transportation.

Ivan Melisa Kakuru, 26, a transgender woman, still picks up her H.I.V. medications at the Mulago clinic. But she often doesn’t have enough money to eat, she said. Ms. Kakuru said she fled her hometown when her father tried to kill her and does not have a place to live.

Her friend Carlos Bahuriire, 36, a transgender man, said he was evicted by his landlord and had been staying with a sympathetic friend.

President Yoweri Museveni has called L.G.B.T.Q. citizens “disgusting” and “abnormal,” and has said that they have “a type of sickness.” He has also blamed the West for bringing homosexuality into the country.

Ugandan police have falsely accused activists or educators — like those arrested in Jinja — of recruiting children into homosexuality and making pornographic videos. Some government officials also have conflated homosexuality with pedophilia.

“If you start raping children and so on, we kill you,” Mr. Museveni said last year of the law.

Dr. Aceng, the health minister, celebrated the passing of the law. “Our culture and dignity is upheld and the Ugandan Children Protected,” she wrote on X.

The criminalization of homosexuality actually is a leftover of colonialism and takes Uganda out of step with the rest of the world, said Matthew Kavanagh, director of the Global Health Policy and Politics Initiative at Georgetown University.

The President’s Emergency Plan for AIDS Relief provides more than $400 million in H.I.V. funding to Uganda each year. More than 96 percent of that is implemented by organizations outside the Ugandan government.

Now the Biden administration has redirected $5 million of the rest away from the government, Ambassador Popp said.

As of Jan. 1, the United States has removed Uganda’s access to the African Growth and Opportunity Act, which provides duty-free access to the U.S. market. Washington has also sanctioned Johnson Byabashaija, commissioner general of the Uganda Prisons Service, for torture and human rights abuses.

But Dr. Kavanagh and other experts said the Biden administration could do more to impose financial sanctions or pressure the Ugandan government to repeal the law.

Mr. Byabashaija’s sanction was based in part on evidence from the March 2020 arrest of Henry Mukiibi, who leads an H.I.V. clinic and shelter, along with 19 others.

The group was held for 52 days, during which they were tortured and beaten; some had their genitals burned with a piece of firewood, Mr. Mukiibi said in an interview.

“Whenever I talk about this instance, I get nightmares,” he said. “It traumatized me.”

Last July, the organization was again raided and the clinic was shut down. Undeterred, Mr. Mukiibi has moved to a new secure location.

Mr. Mukiibi said he felt it was important to speak up. “Sometimes when we hide things, or when the person who’s speaking becomes anonymous, people don’t understand the exact situation you’re passing through,” he said.