Community MRSA infections rising in people with HIV/AIDS

'It's an alarming trend because these strains are very hardy.'

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infection has become a growing problem in HIV/AIDS patients, clinicians and researchers report.

"This is definitely an emerging phenomenon with community-acquired MRSA," says Tony Trinh, MD, an internal medicine resident at the Warren Alpert Medical School of Brown University and Rhode Island Hospital in Providence, RI.

"It's emerging in the general population and in the HIV population," Trinh adds. "It's an alarming trend because these strains are very hardy, and they obviously tend to go in circles and groups of people who are at high risk."

Also, CA-MRSA can be life-threatening if it migrates to the blood stream or causes pneumonia, he says.

Research also has shown a statistical association between HIV and CA-MRSA among an HIV population investigators studied in Chicago, IL, says Kyle Popovich, MD, an infectious diseases physician at the Rush University Medical Center in Chicago.

According to published studies, CA-MRSA infections are being observed nationally, in particular with skin and soft tissue infections, in outpatient clinics and emergency rooms, Popovich says.

"So while our study looked at this HIV population, what we saw is going along with what's in the literature for the United States," she says.

A 2007 study found that CA-MRSA rates have increased significantly among HIV-infected population since 2003. The incidence was 40.3 cases/1000 person-years in 2005, an 18-fold higher than general population incidence among the population served at a large HIV clinic in Bethesda, MD.1

The same study found that 90% of the CA-MRSA infections were skin and soft-tissue infections, and 21% of patients experienced a recurrent infection.

Other affected populations

CA-MRSA infections have emerged nationally among children, athletes, prisoners, and military personnel, Popovich notes. Close proximity and shared items have been cited as among the likely reasons.

"It's unclear why certain populations are being affected, and now we're seeing community-acquired MRSA even among people who are not part of these populations, so it's spreading," she says.

"The recent growth of CA-MRSA cases has been higher among HIV-positive individuals than among HIV-negative individuals in the population we examined," she adds.

Trinh's research has observed that CA-MRSA patients often present with skin and soft-tissue infections. The key is for HIV clinicians to maintain a high level of suspicion of possible CA-MRSA when their patients have skin infections, he says.

"If you drain an abscess, send it to culture, then you'll know what kind of strain it is, and it's easy to identify from the microbiological standpoint," Trinh says. "From the clinical standpoint, patients show up with these abscesses and are not comfortable because these are painful."

Popovich and co-investigators reviewed cases and found that HIV patients with CA-MRSA and skin and soft-tissue infections were often seen in outpatient clinics and emergency rooms.

"Studies have shown that skin and soft-tissue infections in some ERs are very common," Popovich says.

Among the HIV patients that were hospitalized with CA-MRSA skin and soft-tissue infection, the study population was predominantly African American and male. More than 80% were black, and 72% were men, and the mean age was around 40 years. Other common characteristics included a history of illicit drug use among 61% and men who have sex with men (MSM) among 22%.2

"We looked at people who were hospitalized, and we looked at intensive care unit admission," Popovich says. "We focused on skin and soft tissue infections, but didn't look at bloodstream infections."

The MRSA strain is particularly adapted to skin and soft-tissue infections, Trinh notes.

Treatment options

Patients with CA-MRSA skin and soft-tissue infections can be treated on an outpatient basis with trimethoprim-sulfamethoxazole or tetracycline. In Trinh's study, antibiotic susceptibility was high with these two medications at 96.5% for tetracycline and 95.2% for trimethoprim-sulfamethoxazole.3

Although CA-MRSA has virtually no resistance to vancomycin and rifampin, these drugs aren't good candidates for first-line treatment because they would need to be administered in an intravenous form that is expensive and would require an inpatient setting, Trinh says.

Treatment also includes incision and drainage, which can be done by surgeons or by physicians in primary care or HIV clinics.

The key is following the principle of having adequate source control and treating abscesses that are larger than three or four centimeters, Trinh says.

In another study there was a high rate of recurrence of CA-MRSA among HIV patients, particularly in a population seen at the Naval Medical Center San Diego between 2000 and 2007. The population was almost entirely male, predominantly Caucasian (58%), followed by Hispanics (23%), and African Americans (16%).4

Popovich's study also found a statistical association of having a high CA-MRSA infection rate in communities with high rates of prison exposure, Popovich says.

"We don't know what that means, and we need to research further to tease that out," she adds.

What makes the skin and soft-tissue CA-MRSA cases different is that traditionally MRSA has emerged in health care facilities as an infection that is acquired in hospital settings, Popovich says.

HIV-infected patients have a high incidence of CA-MRSA skin and soft-tissue infections, according to another U.S. study.5 A retrospective review of 900 HIV-infected outpatients from January, 2002, to December, 2007, showed that 8% were colonized or infected with MRSA.

The same research concluded that HIV-infected patients at significant risk for MRSA were those who had a CD4 cell count of less than 200 cells and who had antibiotic exposure. Patients who had been on antiretrovirals for the previous year had a significantly reduced risk of MRSA colonization.

Trinh's study concluded that most patients with CA-MRSA did not have immunological/virological markers consistent with severe HIV/AIDS disease. HIV and CA-MRSA have an intriguing relationship, Trinh says.

While Trinh's research did not show a relationship between AIDS-defining illness and CA-MRSA infection, there definitely is an immune deficiency related aspect to why HIV patients are presenting with these soft-tissue infections, Trinh explains.

"It's not wholeheartedly explained by immune deficiencies that come with HIV, but these are alluding to possible processes that are not well-defined yet," he adds.

Another new study found that CA-MRSA is prevalent in wounds of injection drug users (IDUs), which potentially could be a factor in the rising rate of CA-MRSA among an HIV population and in some other groups. The study sampled 218 people from a community-recruited cohort of IDUs at a supervised injection facility and found that 27% had at least one wound and 43% of these wounds were positive for S. aureus, of which more than half were MRSA. 6

The skin and soft-tissue manifestation of CA-MRSA can be treated in outpatient settings, but there are cases where it causes more invasive disease and enters the bloodstream, she adds.

For HIV clinicians the take-home message is to continue good infection disease control practices, such as washing hands with soap and water between each patient, and teaching patients to practice better hygiene at home.

"If an HIV patient has a wound or scrape, he or she should keep it covered," Popovich says. "If they're changing family members' bandages, they should wash hands and avoid contact with wounds or bandages, and avoid sharing personal items."

Diagnosing the infection can be fairly straightforward. Patients may notice a mark on their skin that looks like a spider bite, she says.

"Typically, it's described as an area of the skin that's warm and inflamed," Popovich says.

"In some areas, there is an increased awareness of the CA-MRSA epidemic," she adds. "However, education on proper infection control practices and prevention measures is still needed."


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