Community-acquired MRSA strain spreading in L.A.

Resistant bug spreading in community, jails

In another sign that a dangerous nosocomial pathogen is no longer confined to the hospital, a distinct strain of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) is emerging in Los Angeles, public health officials report.

Three community outbreaks of skin infections associated with MRSA occurred in that area in 2002, including transmission within athletic teams and correctional facilities. The Centers for Disease Control and Prevention (CDC) is assisting in the investigation as part of its national effort to track the emergence of MRSA beyond the hospital. The CDC is working with California and three other states in a project to define the spectrum of disease, determine populations affected, and define those at particular risk for infection.

"We are looking at entire populations and capturing all of the MRSA cases that occur, and then determining whether they have any association with health care," says John Jernigan, MD, medical epidemiologist in the CDC division of healthcare quality promotion.

"It is a little too early to say if there is a huge emergence, but we are able to define a specific population that has no established risk factors for health care-associated MRSA," he says. "The question is: Do the bacteria act differently from either usual community staphylococcus or MRSA that is familiar to health care facilities? It appears that there are some differences."

In Los Angeles, as in other areas where the pathogen has emerged in the community, those infected do not report the traditional risk factors (i.e., recent hospitalization, surgery, residence in a long-term care facility, or injecting drug use). Molecular analysis of the isolates confirms the spread of a single, predominant MRSA strain in that area. In past cases of MRSA in the community, there has been some debate about whether the pathogen was arising primarily due to massive use of antibiotics or transmission from person to person. The latter seems to be the primary explanation in the Los Angeles outbreaks, says Jernigan. "It is possible that antibiotic pressure is one of the factors that drives the development of MRSA in a person, but there are a lot of transmissions that may occur that we simply are not aware of," he points out.

In September 2002, investigators reported that two athletes on the same sports team were hospitalized with MRSA within the same week. No additional cases of MRSA have been identified, and the source of MRSA infection in the athletes has not been determined. Last November, physicians from two large infectious disease clinical practices in Los Angeles notified public health officials of increasing MRSA skin infections among men who have sex with men (MSM).

"It appears that it is emerging in the community," Jernigan says. "We know that one aspect of that is in the MSM community."

MRSA is not emerging specifically as a sexually transmitted disease in the MSM community but as a result of transmission via skin-to-skin contact, he adds.

"We have investigated Native American communities where they have identified MRSA transmission from the benches of sweat lodges," he says. "From sports teams, we know that the sharing of towels, sports equipment, and benches can be a source of MRSA."

In addition, there is an ongoing outbreak of MRSA in the Los Angeles County Jail, where 928 inmates had MRSA wound infections diagnosed in 2002. Many of the skin infections were initially reported as spider bites, but serious systemic infections resulted in some cases. Review of medical charts of 39 of the 66 inmates hospitalized with the infections indicated that all initially had skin infections. Ten inmates later developed invasive disease, including bacteremia, endocarditis, or osteomyelitis. The Los Angeles County Jail is the largest jail system in the United States, with 165,000 prisoners incarcerated each year. Is it possible the prison system could emerge as a reservoir for community-acquired MRSA much in the same way that nursing homes and hospitals have?

"That is an excellent question, but we haven’t yet done [enough] investigation to show the connection between the community and the correctional facility — where the correctional facility is a nidus for MRSA," Jernigan says. "We do know that there is quite a lot of movement; we’ve seen the spread of MRSA from [jail] facility to facility. Clearly, [inmates] are going to be going back into the community, and you can have spread that way. Whether that is a significant contributing force, I don’t know."

In light of the outbreaks, Los Angeles health officials have issued recommendations for the diagnosis and treatment of skin infections and are working with correctional officers on policies for laundry, showers, environmental cleaning, skin care, and control of person-to-person transmission in prison. 

"The prison-setting factors include overcrowding and laundry issues," Jernigan says. "In some investigations, we have found that they have not appropriately dried the [prison] jump suits and they have had to wear them wet. There are simple things like not laundering frequently and access to soap. Different correctional facilities will have different policies on how they manage hygiene. Some make [inmates] lock up their soap, so [they] have to go back to [their] room in order to wash [their] hands. There are challenges in that setting that allow for the transmission of MRSA."

The outbreaks remain under investigation, and no clear line has been established yet between the prison population and the MSM community in Los Angeles. One thing is clear; the antimicrobial susceptibility patterns from MRSA isolates of all cases have been similar. The predominant strain in the outbreak is susceptible to TMP/SMX (Bactim or Septra), clindamycin, gentamicin, and rifampin. The MRSA strain is resistant to both fluoroquino-lones, and the beta-lactam class of antibiotics for which methicillin has become the common marker.

"The antibiotic pattern actually does appear different than what a hospital pattern looks like," Jernigan says. "The presence of fluoroquinolone [resistance] is not necessarily new, but usually you see less resistance in the community-acquired pathogens."

Such cases raise important diagnostic and antibiotic treatment questions because clinicians who do not suspect community-acquired MRSA may prescribe ineffective empiric regimens, a factor that likely contributed to at least some of the more serious infections in Los Angeles. However, that aspect of the outbreaks remains under investigation.

"We actually don’t know [yet] whether or not there is an association between the severity of illness and the antimicrobial resistance of the pathogen," he says.