New multi-drug-resistant bacteria emerge in U.S. cities on both coasts

(revised 1-23-08)

A multi-drug-resistant variant of community MRSA bacteria is emerging in cities on both coasts of the U.S., a new UCSF-led study shows.

The research found that men who have sex with men were at higher risk for infection with a multi-drug-resistant variant of the so-called MRSA USA300 bacteria. The study because of its retrospective nature was unable, however, to assess causes or links between the multi-drug-resistant bacteria and specific sexual practices. The bacteria appear to be transmitted most easily through intimate contact, but can also spread by direct contact with contaminated skin or contaminated surfaces.

The research is based on information collected from MRSA cases from nine of 10 medical centers serving San Francisco and medical records from outpatients with MRSA infections who were treated in an HIV clinic in San Francisco and a clinic serving a predominantly lesbian/gay/bisexual/transgender population in Boston. 

Except for its multi-drug-resistance, the variant is closely related to other USA300 MRSA bacteria that have spread beyond hospital borders in recent years and caused outbreaks of severe skin and other infections. Like the less resistant forms, it spreads easily through skin-to-skin contact, invading skin and tissue beneath the skin. MRSA bacteria cause abscesses and other skin infections that can progress rapidly to potentially life-threatening infections if untreated.

The research appears in the January 14 early online edition of the “Annals of Internal Medicine.” It will appear in the print edition February 19.

The study showed that the multi-drug-resistant MRSA strain has emerged throughout San Francisco. It is found in other cities, as well. One part of the study, based on patient medical charts in the San Francisco clinic, showed that HIV-positive patients who reported their risk factor for HIV as being men who have sex with men were about 13 times more likely to be infected with the multi-drug-resistant variant than patients who reported some other risk factor for HIV. 

About one in 588 people living in San Francisco’s Castro district was infected with the multi-drug- resistant MRSA bacteria, the study shows. About one in 3800 San Franciscans overall was infected. Both are surprisingly high numbers, says Binh Diep, PhD, UCSF postdoctoral scientist at San Francisco General Hospital Medical Center and lead author of a report on the finding.

The statistics come from the scientists’ study of MRSA samples previously collected from patients in San Francisco medical centers.

“These multi-drug-resistant infections can affect men who have sex with men at body sites in which skin-to-skin contact occurs,” says Diep. “However, these same body sites can be infected by MRSA in other individuals as well, so it is not possible to determine from the study what role sexual transmission plays per se.”  Regardless, a good scrubbing with soap and water may be the most effective way to prevent skin-to-skin contact transmission, including after sexual activities, Diep says.

MRSA stands for methicillin-resistant Staphylococcus aureus. Until recently, MRSA bacteria were confined to hospitals, where extensive use of antibiotics has prompted highly resistant strains to evolve. MRSA is resistant to the antibiotic methicillin and closely related drugs, while the variant studied in the new research is resistant to a number of other antibiotics, making it harder to treat. The spread of multi-drug-resistant MRSA into communities, first reported by the UCSF team in 2006 (Lancet. 2006:367:731-9), has led to heightened concern. 

“Prompt diagnosis and the right treatment are crucial to prevent life-threatening infections and the spread of this bacteria to close contacts,” says Henry Chambers, MD, a senior author of the study and UCSF professor of medicine at San Francisco General Hospital Medical Center. Chambers is lead scientist of a large multi-centered clinical trial recently funded by the National Institutes of Health to study treatment of community-associated MRSA infections.

The study was largely funded by the Centers for Disease Control and Prevention and a Pfizer grant.

Coauthors on the paper and collaborators in the study are UCSF scientists Christopher J. Graber, MD, MPH; Francoise Perdreau-Remington, PhD; Tiffany HaiVan Phan, BA; and Heather Carleton, MPH, all at San Francisco General Hospital Medical Center.

Also: John Szumowski, MD, MPH at Beth Israel Deaconess Medical Center; Loren Miller, MD, MPH, at Harbor-UCLA Medical Center; Linda Han, MD, at State Laboratory Institute, Jamaica Plain, Mass.; Jason Chen, BA; Felice Lin, BA; Jessica Lin, BA;  and George Sensabaugh, DCrim, all of the School of Public Health, UC Berkeley; Linda McDougal, MS, and Fred Tenover, PhD, both at the Centers for Disease Control and Prevention; Daniel Cohen, MD, Fenway Community Health, Boston; and Kenneth Mayer, MD, Brown University/Miriam Hospital, Rhode Island.

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