Community-acquired methicillin-resistant Staphylococcus aureus infections hit Los Angeles. (Young, Otherwise Healthy Women Affected).

LOS ANGELES -- Public health officials are investigating an outbreak of an aggressive, community-acquired, methicillin-resistant Staphylococcus aureus skin infection that has struck more than 1,000 people, including newborns, young athletes, healthy women, gay men, and prisoners in Los Angeles over the past year.

Federal officials said the outbreak of community-acquired methicillin-resistant S. aureus (MRSA) appears to be the largest ever reported in the United States.

Several unusual features of the cases have officials worried, including the fact that patients have included otherwise healthy, community-dwelling adults and newborns, as well as people with HIV, and male and female prisoners who share dose quarters.

The infection appears on seemingly intact skin as "a little boil that very quickly looks very bad," said Dr. Elizabeth Bancroft, medical epidemiologist with the Los Angeles County Department of Health Services.

Very aggressive treatment is required, sometimes including surgical debridement and lengthy hospital stays for patients to receive intravenous antibiotics to which the organism is sensitive.

"We all knew MRSA was going to escape into the community, we just didn't know how. The frightening thing is the virulence with which it happened," said Margie A. Morgan, Ph.D., a microbiologist at Cedars-Sinai Health System, where pulsed-field gel electrophoresis showed that samples from a dozen patients in Los Angeles shared a "virtually identical" genetic fingerprint.

In turn, isolates from her lab were found to be a clonal match with samples from an MRSA outbreak among gay men in New York City in 1997.