Injection drug users who abuse opioids such as heroin are more susceptible to infections than other people.Credit: Spencer Platt/Getty

Opioid addiction kills tens of thousands of people every year in the United States and the trend shows no signs of slowing. Now, public-health officials are worried about a surge in bacterial and viral infections linked to opioid misuse that threatens to compound the crisis.

This surge includes an unprecedented rise in bacterial infections — including those caused by Staphylococcus aureus, a bacterium that’s frequently resistant to antibiotics — and a spike in new cases of HIV and hepatitis associated with injecting opioids that risks undoing decades of progress in corralling these diseases.

Research groups around the country are working to understand, identify and treat these outbreaks. But the lack of solid data on the number of new cases, and where they’ll crop up next, as well as stigma associated with drug use that can prevent people with infections from seeking early treatment, is hindering efforts.

“This is like HIV all over again,” says Judith Feinberg, an infectious-disease physician at West Virginia University in Morgantown, comparing the current crisis to the HIV epidemic that dominated US public health efforts in the 1980-90s. “People are stigmatized; they don’t feel they deserve to live. They hear people say it’s a lifestyle choice.”

Over the past 20 years, the use of opioids, including prescription pain medications, heroin and synthetic drugs such as fentanyl, has skyrocketed in the United States. As of 2017, there were roughly 15 opioid-overdose-related deaths per 100,000 people in the country, compared with 3 per 100,000 in 1999, according to estimates from the US Centers for Disease Control and Prevention.

An affair of the heart

One type of opioid-related infection that researchers are grappling with involves diseased heart valves. Bacteria such as S. aureus can enter the bloodstream as a result of practices such as needle sharing or not cleaning the skin before injecting a drug. If the infection reaches the heart, it can damage the valves. Severe cases can require a heart transplant.

In an ongoing study, microbiologist Cecilia Thompson at the University of North Carolina in Chapel Hill is sequencing DNA from heart valves collected from people who have had surgery to replace diseased valves with artificial ones. Thompson found that valves taken from people who had injected drugs were more likely to be infected with S. aureus than were those of non-users.

Thompson presented her results at the American Society for Microbiology meeting in San Francisco, California, on 21 June. But these are just the latest observations of what seems to be a worrying trend. In a study published in January1, researchers found a 13-fold increase in heart infections among people who misuse drugs in North Carolina between 2007 and 2017. Until 2013, surgeons in the state used to perform fewer than 10 operations to treat drug-related heart infections, compared with more than 100 in 2017.

Opioids themselves — rather than the method used to inject them — could also be making people more susceptible to infection. Another study2, also published in January, looked at more than 25,000 people treated at veterans’ health facilities between 2000 and 2012. It found that people who took medium or high doses of prescribed opioids for pain management — especially people with HIV — were significantly more susceptible to pneumonia. It’s unclear why, but research in monkeys suggests that some prescription opioids, such as morphine, suppress the immune system3.

In response to these results, researchers are devising ways to improve the diagnosis and treatment of infections — whether they’re bacterial, viral or fungal — in opioid users. Identifying the pathogen that is causing an infection is crucial to treating it properly. Thompson says that her group plans to use next-generation sequencing techniques, which can test for a wider array of microbes in blood and tissue samples than current methods, to help them with their work.

Catching the culprit

Even when researchers know what’s causing an infection, the pattern of outbreaks associated with drug use may differ from that of non-drug-related ones. This makes it difficult to anticipate where infections will occur.

But a computer model developed by Georgiy Bobashev, a data scientist at RTI International, a non-profit research institute in Research Triangle Park, North Carolina, and his colleagues simulates drug users and their social networks to predict the location of opioid-related HIV outbreaks. The program considers factors including whom users know, the type of heroin available to them — which could affect the presence of pathogens — and their experience with the drug.

The social component to predicting these outbreak patterns is crucial, Bobashev says. People who used drugs during the height of the HIV epidemic in the 1990s learnt safe injection practices, he says, but newer users are more likely to use riskier methods, such as sharing needles. “They don’t have good practices and they don’t have good connections with people who have been injecting drugs for a long time,” Bobashev says.

In an unpublished analysis, his group’s model predicted that HIV outbreaks related to opioids would be concentrated within small geographic pockets, rather than spread over a wider area, as researchers would expect with non-drug-related outbreaks.

Data from real life bolster this result. Previous opioid-related HIV outbreaks, including one in 2014 in Scott County, Indiana, followed this pattern. And in March, the West Virginia health department announced an outbreak in Cabell County due to a spike in new cases of HIV acquired through drug use. Historically, sex was the primary mode of HIV transmission, according to the state’s health department.

The key to preventing and stopping the rise in opioid-associated infections is to treat opioid use as a disease without stigmatizing people who misuse drugs, says Carlos Del Rio, a global-health researcher at Emory University in Atlanta, Georgia.

A working group at the US National Academy of Medicine, which Del Rio is leading, has started to develop a strategy for integrating care for infections and opioid use. “The opioid epidemic is going to be to [young medical students] what HIV was to me,” Del Rio says. “You’d better get used to it.”