Researchers in Tennessee have identified another indirect impact stemming from the nation's ongoing opioid epidemic: a rise in the most dangerous type of staph infection.

In a study published this week in Emerging Infectious Diseases, epidemiologists from the Tennessee Department of Health and Vanderbilt University report that nearly a quarter of the community-onset methicillin-resistant Staphylococcus aureus bloodstream infections (CO MRSA BSIs) identified in the state from 2015 through 2017 were related to injection drug use (IDU). During that period, IDU-related cases more than doubled.

The study also found that cases linked to drug use were more common among white, uninsured women between the ages of 18 and 49.

The findings could help explain why CO MRSA BSI rates rose by more than 37% from 2011 through 2016 in Tennessee, while remaining steady nationwide.

Although MRSA BSIs are typically associated with previous healthcare procedures and hospitalization, use of commonly injected drugs like heroin and the synthetic opioid fentanyl is also a known risk factor, because MRSA typically lives on the skin and can easily get into the bloodstream, especially if users don't clean their skin or are reusing needles. And in Tennessee, as in other states, opioid abuse in recent years has shifted from prescription opioids to heroin and fentanyl.

"If you are injecting anything through your skin directly into the bloodstream, that is a prime opportunity to introduce bacteria into your bloodstream, especially if you are not using safe injection practices," said lead study author Meghana Parikh, VMD, MPH, an epidemiologist with the Tennessee Department of Health.

An alarming trend

To explore what might be behind the rise in CO MRSA BSI cases across the state, Parikh and her colleagues used the National Healthcare Safety Network database and the Tennessee Hospital Discharge Data System to identify MRSA BSIs diagnosed in patients over the age of 13 and to further characterize the demographics and clinical aspects of those cases.

Cases were identified as IDU-related if a hospital visit in the 6 months before or after the MRSA BSI diagnosis contained a diagnostic code for drug use. Cases were classified as community-onset if the culture was obtained on or before the third day of hospitalization.

Overall, the team identified 7,646 MRSA BSI cases from January 2015 through December 2017, and found a 17.7% increase in cases over the 2-year period (from 2,333 in 2015 to 2,746 in 2017).

Nearly 90% of the cases were community-onset, with 57% diagnosed in the emergency department. IDU-related cases represented 24.1% of the overall cases, and rose from 375 in 2015 to 821 in 2017—a 118% increase. IDU-related cases diagnosed in the emergency department rose by nearly 200%.

"That was incredibly alarming to us," Parikh said.

Analysis of demographic characteristics among the CO MRSA BSI patients revealed that the median age of IDU-related BSIs was 40 years (versus 63 for non-IDU-related cases), and that 69.7% of the IDU-related cases occurred in 18- to 49-year-olds. Just over half of the IDU-related cases were women, and 88.9% were white. Roughly a third were uninsured.

"Our IDU-related patients tend to be much younger, they tend to be more often white, and also uninsured," Parikh said. "Those are the demographics that seemed to really jump out at us."

The prevalence of endocarditis, hepatitis C, and skin and other soft-tissue infections—conditions that tend to be associated with injection drug use—was also significantly higher than in non-IDU-related cases. And more than one additional IDU-related diagnosis was found in 84.2% of IDU-related MRSA BSI cases.

Changing demographics

These findings are significant, Parikh said, because they represent a shift in the demographics typically associated with MRSA BSIs, which are the most dangerous type of staph infection and can cause severe illness and death. Historically, most MRSA BSI cases have been hospital-onset, occurring in older inpatients with multiple comorbidities not related to drug use.

But the types of patients identified in the study, and the high prevalence of community-onset infections, might signify that hospitals need to approach MRSA BSI prevention and treatment differently.

Over the past two decades, prevention and treatment strategies have focused on hospital-onset MRSA infections, and those strategies have had an impact. According to a March 2019 CDC report, hospital-onset MRSA BSIs fell by 17.1% a year from 2005 through 2012, before levelling off from 2013 through 2016. Community-onset MRSA BSIs have declined slower, however, while methicillin-susceptible S aureus BSIs have climbed. CDC officials suggested at the time of the report that these trends could be linked to the nationwide opioid epidemic.

At the very least, Parikh believes the findings of the study can help heighten awareness among emergency department clinicians that these younger, female MRSA BSI patients may be injection drug users.

"We're suggesting that maybe if we're seeing more and more people coming into the emergency department with MRSA BSI, and they tend to be younger females, and also white, that maybe we also need to be looking at these other injection drug use–related events as well," she said.

The fact that CO MRSA BSI patients are more likely to be uninsured, Parikh and her colleagues write in the study, could also have implications for follow-up care, because those patients may be less likely to afford follow-up treatment.

"We need to be considering how we can follow up with them better," she said.

In addition, Parikh suggested that these findings could start a conversation about the role that hospitals can play in helping opioid addicts get the treatment they need. She noted that previous studies have found that interventions like medication-assisted therapy and screening and referral to treatment can be effective in acute-care settings but have been underused.

"Maybe this paper could be a conversation starter to see if there's a way that we can incorporate addiction treatment more into our acute-care settings," she said.

See also:

Feb 12 Emerg Infect Dis study

Mar 5, 2019, CIDRAP News story "CDC: Progress stalled against staph, MRSA infections"