Mpox Often Leads to Severe Illness, Even Death, in People With Advanced H.I.V.

In people with advanced H.I.V. disease, the mpox virus — formerly known as monkeypox — often causes severe illness, with a death rate of about 15 percent, researchers reported on Tuesday.

The seriousness of the infection warrants the inclusion of mpox among the opportunistic conditions that are particularly dangerous to people with advanced H.I.V., the researchers said at the Conference on Retroviruses and Opportunistic Infections in Seattle.

“These findings make it very, very clear that every single person with mpox should have an H.I.V. test,” said Dr. Chloe Orkin, an H.I.V. expert at Queen Mary University of London and the researcher who led the work. She and her colleagues also described the results in the journal The Lancet on Tuesday.

The mpox outbreak began unfolding last May. Although the number of cases has slowed to a trickle in most regions, it has so far affected roughly 86,000 people in 110 countries and killed 92. Multiple studies estimated that from 40 percent to 50 percent of infected individuals were living with H.I.V.

When antiretroviral drugs keep H.I.V. in check, mpox is about as dangerous as it is to those without H.I.V. infection. But a C.D.C. study last year, along with observations from previous outbreaks in Nigeria, indicated that mpox was more severe, and far more lethal, in those with high levels of H.I.V.

In the new study, an international group of clinicians tracked 382 adults in 28 countries who had advanced H.I.V. disease and were infected with mpox. They analyzed the amount of H.I.V. and the number of CD4 cells, a type of immune system cell, in these patients.

The typical range for CD4 cells is from 500 to 1,500 per cubic millimeter of blood. All 27 deaths in the study were among people who had fewer than 200 CD4 cells. Mpox killed nearly 30 percent of those with fewer than 100 CD4 cells.

The nature of the illness was also strikingly different in patients with weakened immune systems. While most people infected with mpox show lesions only at the site of exposure, those with advanced H.I.V. developed large, ulcerated lesions teeming with virus throughout the body.

“It’s on the back, it’s on the feet, it’s in the eyes, it’s everywhere — it’s horrifying,” Dr. Orkin said. “It’s because the immune system is not able to contain the virus at all.”

Many patients also had nodules in the lung that caused acute respiratory distress, she added.

Adding mpox to the list of opportunistic infections in people with advanced H.I.V. would encourage health care workers to identify and prioritize patients most at risk of severe disease and death.

Patients would need antibiotics to prevent other opportunistic infections, and should be offered two doses of vaccine injected under the skin, rather than between layers of the skin as is currently done, Dr. Orkin said.

The United States added mpox to the list of possible opportunistic infections in people with H.I.V. in September. The World Health Organization plans to discuss doing the same over the next few months, said Dr. Meg Doherty, the director of global H.I.V., hepatitis and sexual transmitted infections programs at the W.H.O.

The new data make a “compelling case” for mpox’s addition to the list of opportunistic conditions, Dr. Doherty said.

In parts of the world where people with H.I.V. may not have access to mpox vaccines, or to treatment for mpox and H.I.V., she said, “this should just raise the awareness that we have more to do in those areas than we have.”