The bug most drugs can’t cure

Long history
The bacteria known as staph were discovered in the 1880s, but researchers guess that they are one of mankind’s oldest companions because they display such skill at living with and on us. According to the CDC, about one third of the U.S. population carries staph around on the outside of the body or on mucous membranes, usually in the nostrils; most of us will go unharmed, unless the bug happens to slip through a cut or break in the skin. Because it is one of the most common causes of infections, staph was one of the first targets for antibiotics. In fact, penicillin was discovered because the mold that produced it grew on, and killed, a petri dish full of staph.

But a mere two decades after penicillin’s debut, 80 percent of staph germs had become resistant to the drug. So chemists engineered a chemical cousin, called methicillin, as a substitute. They hoped the latest formula’s protection would last for decades, but the first evidence that staph could resist it appeared within two years. Then staph demonstrated a new trick: It developed additional resistance to a huge class of drugs, called beta-lactams, that share similar chemical structures. Beta-lactam antibiotics (not only penicillin and methicillin, but amoxicillin and cephalexin as well) are the drugs that doctors prescribe routinely for things such as urinary tract infections, pneumonia, ear infections—and staph. With a simple genetic change, MRSA had taken that entire class of drugs out of the physicians’ arsenal.

Drug-resistant staph appeared mainly confined to hospitals until around 1998. “We began seeing perfectly healthy kids with no risk factors coming in from the community with serious infections,” says Robert S. Daum, M.D., professor of pediatrics and chief of pediatric infectious diseases at the University of Chicago. “So we put together a study and found that in five years, the incidence of CA-MRSA infections had increased 25-fold.” The next year, a CDC report revealed that four children in Minnesota and North Dakota had died of overwhelming infections, all of them caused by staph resistant to beta-lactams. -

Suddenly, outbreaks of community MRSA seemed to be everywhere. Disease detectives found it in a prison and in jails, and among military trainees; among Native American users of traditional saunas and gay men who frequented bathhouses; in healthy newborn infants, methamphetamine users and tattoo recipients; and among high school and college athletes and players in the National Football League.

Spreads too fast for tracking
Some of the victims shared common characteristics: They lived in settings such as correctional institutions, where hygiene was hard to maintain, or spent time in hot, wet places such as sweat lodges, where bacteria often thrive and where surfaces might transfer the bug to bare skin. The athletes were more likely to share clothes and equipment and to have contact with each other’s cuts and abrasions. The meth addicts sometimes wounded themselves by scratching their skin raw while they were high. But some had no risk factors at all. And the victims’ sheer diversity made the case that MRSA was spreading faster in the community than it could be tracked.

Studies revealed that the MRSA that was infecting people in the wider world was not the same as the strain that threatened patients inside hospitals: The hospital strain had grown resistant to almost all drugs except for two or three very strong ones, but the community variety was still susceptible to medications outside the beta-lactam class. Molecular analysis showed that the two types of MRSA were genetically different as well, having acquired their drug resistance in different ways.

The two types had an additional, crucial difference. Hospital MRSA still attacked its victims via staph’s traditional route, by slipping into wounds such as surgical incisions and cuts made to accommodate catheters. But the community-associated type had learned something new: It was breaking through skin that appeared healthy and intact. The germ may have the power to slip through tiny abrasions people haven’t noticed, or, some doctors speculate, it might be penetrating skin on its own. The first sign of trouble often looks like an insect bite. And it is often misdiagnosed that way: An outbreak of more than 900 cases in the Los Angeles County jail was discovered when inmates complained about spider bites even after the jail had been doused with insecticide.

An insect bite was Cathy Thrasher’s first thought when the teacher and mother of three from Henderson, Kentucky, spotted a quarter-sized welt on the back of her thigh in August 2005. Thrasher, then 38, had just begun teaching seventh grade, and she was reluctant to interrupt her day to go to the doctor until her school’s nurse insisted.

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