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Overview

Methicilllin-resistant Staphylococcus aureus (MRSA) infection may be one of the most frightening illnesses you've never heard of. Unlike more galvanizing diseases such as smallpox and bird flu, MRSA infection has quietly been killing and maiming hundreds of thousands of vulnerable people, including children, without grabbing a single headline.

One reason may be that staphylococcus aureus bacteria, often simply called staph, are common — they're found on the skin or in the nose of about one-third of the population. The bacteria are generally harmless unless they enter the body through a cut or other wound, and even then they often cause only minor skin problems in healthy people. But in older adults and people who are ill or have weakened immune systems, ordinary staph infections can be deadly.

Decades ago, a strain of staph emerged in hospitals that was resistant to the broad-spectrum antibiotics commonly used to treat it. Dubbed methicillin-resistant Staphylococcus aureus (MRSA), it was one of the first germs to outwit all but the most powerful drugs. Since then, MRSA infection has flourished in hospitals and care facilities worldwide, where it can cause massive infections in bones, joints, the bloodstream and surgical wounds. When not treated properly, MRSA infection is fatal.

In the 1990s, a type of MRSA began showing up in the wider community. Today, that form of staph, known as community-associated MRSA, or CA-MRSA, is responsible for most serious skin and soft tissue infections and for a lethal form of pneumonia.

Vancomycin is one of the few antibiotics still effective against hospital strains of MRSA infection, although the drug is no longer effective in every case. Several drugs continue to work against CA-MRSA, but CA-MRSA is a dangerous and rapidly evolving bacterium, and it may simply be a matter of time before it, too, becomes resistant to most antibiotics.

Signs and symptoms

Unlike hospital-associated MRSA, CA-MRSA produces a deadly toxin (Panton-Valentine leukocidin) that destroys white blood cells and living tissue. The toxin can cause severe, often fatal skin infections (necrotizing, or "flesh-eating," fasciitis) and pneumonia.

MRSA infections start out as small red bumps that can quickly turn into deep, painful abscesses.

 

Causes

Although the survival tactics of bacteria contribute to antibiotic resistance, humans bear most of the responsibility for the problem. Leading causes of antibiotic resistance include:

• Unnecessary antibiotic use in humans. Like other superbugs, MRSA is the result of decades of excessive and unnecessary antibiotic use. For years, antibiotics have been prescribed for colds, flu and other viral infections that don't respond to these drugs, as well as for simple bacterial infections that normally clear on their own.
• Antibiotics in food and water. Prescription drugs aren't the only source of antibiotics. In the United States, about 70 percent of all antibiotics wind up not in people but in beef cattle, pigs and chickens. For the most part, these drugs aren't used to treat disease but to fatten the animals quickly and to prevent illnesses that are common in the unhygienic conditions in which animals are raised. The same antibiotics then find their way into municipal water systems when the runoff from feedlots contaminates streams and groundwater. Routine feeding of antibiotics to animals has become such a threat to public health that the practice is banned in the European Union and many other industrialized countries. Antibiotics given in the proper doses to animals who are actually sick don't seem to produce resistant bacteria.

• Germ mutation. Even when antibiotics are used appropriately, they contribute to the rise of drug-resistant bacteria because they don't destroy every germ they target. Bacteria live on an evolutionary fast track, so germs that survive treatment with one antibiotic soon learn to resist others. And because bacteria mutate much more quickly than new drugs can be produced, some germs end up resistant to just about everything. That's why only a handful of drugs are now effective against most forms of staph.

Hospitals: Germ incubators
MRSA first emerged in hospitals in the 1960s and since then has been nearly unstoppable. It travels from person to person on clothing, cart handles, bedrails and catheters, and even breeds in the water in floral arrangements, leading hospitals in the United Kingdom to ban flowers in critical care units. Evading every effort to control it, MRSA accounts for half of the major complications in hospitalized people and for tens of thousands of deaths every year.

Scientists think hospital-acquired MRSA is particularly virulent and tenacious because it hides and replicates in a common type of amoeba — a single-celled organism that's present on most surfaces. Amoebas can spread in the air, which means that MRSA may be transmitted without human contact. What's more, germs that breed in amoebas are stronger and more drug-resistant than other pathogens are.

CA-MRSA: Right under your nose
MRSA was confined to healthcare settings until the late 1990s, when four previously healthy children in the Midwest died suddenly of massive MRSA infections. Around the same time, athletes began showing up with hard-to-treat boils, and inmates in some U.S. prisons developed deep abscesses that didn't respond to antibiotic treatment. MRSA also turned up among military recruits and some gay men.

It's likely that what is now called community-associated MRSA (CA-MRSA) entered the wider world in the nostrils of people who picked up the bacteria in hospitals. The Centers for Disease Control and Prevention estimates that at least 1 percent of the population, or 2 million people, now carry CA-MSRA in their noses. Carriers may not be sick, but they can spread the infection and run the risk of becoming ill themselves.

The bacteria spread mainly through skin-to-skin contact and through small cuts and abrasions. Overcrowding and poor hygiene also encourage the spread of staph. Once CA-MRSA enters the body, it causes boils and abscesses and, like hospital strains, sometimes sparks massive infections in the bone, blood or lungs.

Risk factors

Because hospital and community strains of MRSA generally occur in different settings, the risk factors for the two strains differ.

Risk factors for hospital-acquired MRSA include:

• A current or recent hospitalization. Despite attempts to eradicate it, MRSA remains the scourge of hospitals, where it attacks the most vulnerable — older adults and people with weakened immune systems, burns, surgical wounds or serious underlying health problems.
• Residing in a long-term care facility. MRSA is far more prevalent in these facilities than it is in hospitals. Most people admitted to a care facility are likely to carry MRSA and have the ability to spread it, even if they're not sick themselves.
• Invasive devices. People who are on dialysis, are catheterized, or have feeding tubes or other invasive devices are at especially high risk.

These are the main risk factors for CA-MRSA:

• Young age. CA-MRSA can be particularly deadly in children, sometimes ravaging their bodies in a matter of hours. The bacteria usually enter through a cut or scrape but can quickly cause a massive systemic infection. Children and young adults are also much more likely to develop necrotizing pneumonia than older people are. Children may be susceptible because their immune systems aren't fully developed or they don't yet have antibodies to common germs.
• Participating in contact sports. CA-MRSA has crept into both amateur and professional sports teams. The bacteria spread easily through cuts and abrasions and skin-to-skin contact.
• Sharing towels or athletic equipment. Although few outbreaks have been reported in public gyms, CA-MRSA has spread among athletes sharing razors, towels, uniforms or equipment.
• Having a weakened immune system. People with weakened immune systems, including those living with HIV/AIDS, are more likely to have severe CA-MRSA infections.
• Living in crowded or unsanitary conditions. Outbreaks of CA-MRSA have occurred in military training camps and in dozens of American and European prisons, killing some inmates and infecting guards and other staff.
• Recent hospitalization or antibiotic use. A recent hospital stay or treatment with fluoroquinolones (ciprofloxacin, ofloxacin or levofloxacin) or cephalosporin antibiotics can increase the risk of CA-MRSA.
• Association with health care workers. People who are in close contact with health care workers are at increased risk of serious staph infections. MRSA can travel through families, passing between parents and children on shared clothing, towels and other personal items.

Risk factors

Because hospital and community strains of MRSA generally occur in different settings, the risk factors for the two strains differ.

Risk factors for hospital-acquired MRSA include:

• A current or recent hospitalization. Despite attempts to eradicate it, MRSA remains the scourge of hospitals, where it attacks the most vulnerable — older adults and people with weakened immune systems, burns, surgical wounds or serious underlying health problems.
• Residing in a long-term care facility. MRSA is far more prevalent in these facilities than it is in hospitals. Most people admitted to a care facility are likely to carry MRSA and have the ability to spread it, even if they're not sick themselves.
• Invasive devices. People who are on dialysis, are catheterized, or have feeding tubes or other invasive devices are at especially high risk.

These are the main risk factors for CA-MRSA:

• Young age. CA-MRSA can be particularly deadly in children, sometimes ravaging their bodies in a matter of hours. The bacteria usually enter through a cut or scrape but can quickly cause a massive systemic infection. Children and young adults are also much more likely to develop necrotizing pneumonia than older people are. Children may be susceptible because their immune systems aren't fully developed or they don't yet have antibodies to common germs.
• Participating in contact sports. CA-MRSA has crept into both amateur and professional sports teams. The bacteria spread easily through cuts and abrasions and skin-to-skin contact.
• Sharing towels or athletic equipment. Although few outbreaks have been reported in public gyms, CA-MRSA has spread among athletes sharing razors, towels, uniforms or equipment.
• Having a weakened immune system. People with weakened immune systems, including those living with HIV/AIDS, are more likely to have severe CA-MRSA infections.
• Living in crowded or unsanitary conditions. Outbreaks of CA-MRSA have occurred in military training camps and in dozens of American and European prisons, killing some inmates and infecting guards and other staff.
• Recent hospitalization or antibiotic use. A recent hospital stay or treatment with fluoroquinolones (ciprofloxacin, ofloxacin or levofloxacin) or cephalosporin antibiotics can increase the risk of CA-MRSA.
• Association with health care workers. People who are in close contact with health care workers are at increased risk of serious staph infections. MRSA can travel through families, passing between parents and children on shared clothing, towels and other personal items.

When to seek medical advice

Keep an eye on minor skin problems — pimples, insect bites, cuts and scrapes — especially in children. If wounds become infected, see your doctor. Ask to have any skin infection tested for MRSA before starting antibiotic therapy. Drugs that treat ordinary staph aren't effective against MRSA, and their use could lead to serious illness and more resistant bacteria.

Screening and diagnosis

Most often, doctors diagnose MRSA by checking a tissue sample or nasal secretions for signs of drug-resistant bacteria. The sample is sent to a lab where it's placed in a dish of nutrients that encourage bacterial growth (culture). But because it takes about 48 hours for the bacteria to grow, infected people may continue to spread MRSA while awaiting test results, and those who are already ill can become worse or, in the most serious cases, die. Newer tests that can detect staph DNA in a matter of hours are available, but they're more expensive than culture tests, and most hospitals don't yet use them.

Treatment

Although resistant to many common antibiotics, both hospital and community strains of MRSA still respond to certain medications. In hospitals and care facilities, doctors generally rely on the last-ditch antibiotic vancomycin to treat resistant germs. CA-MRSA may be treated with vancomycin or other antibiotics that have proved effective against particular strains. Although vancomycin saves lives, its constant use makes it more likely that germs will soon grow resistant to it as well; some hospitals are already seeing outbreaks of vancomycin-resistant MRSA. To help reduce that threat, doctors often drain abscesses caused by MRSA rather than treat the infection with drugs.

Prevention

Every year, about 2 million Americans develop hospital-acquired infections and 90,000 die of them. Many of these are the result of MRSA, one of the most virulent and tenacious of the antibiotic-resistant germs. Hospitals are fighting back by instituting surveillance systems that track bacterial outbreaks and by investing in products such as antibiotic-coated catheters and gloves that release disinfectants. Still, the best way to prevent the spread of germs is for health care workers to wash their hands frequently, to properly disinfect hospital surfaces and to take other precautions such as wearing a mask when working with people with weakened immune systems.

Here's what you can do to protect yourself, family members or friends from hospital-acquired infections.

• Ask all hospital staff to wash their hands before touching you — every time.
• Wash your own hands frequently.
• Make sure that stethoscopes and other instruments are wiped with alcohol before use.
• Ask to be bathed with disposable cloths treated with a disinfectant rather than with soap and water.
• Make sure that intravenous tubes and catheters are inserted and removed under sterile conditions; some hospitals have dramatically reduced MRSA blood infections simply by sterilizing patients' skin before using catheters. Better yet, avoid having a urinary tract catheter whenever possible.

Preventing CA-MRSA
Protecting yourself from CA-MRSA — which might be just about anywhere — may seem daunting, but these common-sense precautions can help reduce your risk:

• Keep personal items personal. Avoid sharing personal items such as towels, sheets, razors, clothing and athletic equipment. MRSA spreads on contaminated objects as well as through direct contact.
• Keep wounds covered. Keep cuts and abrasions clean and covered with sterile, dry bandages until they heal. The pus from infected sores often contains MRSA, and keeping wounds covered will help keep the bacteria from spreading.
• Sanitize linens. If you have a cut or sore, wash towels and bed linens in hot water with added bleach and dry them in a hot dryer. Wash gym and athletic clothes after each wearing.
• Wash your hands. In or out of the hospital, careful hand washing remains your best defense against germs. Scrub hands briskly for at least 15 seconds, then dry them with a disposable towel and use another towel to turn off the faucet. Carry a small bottle of hand sanitizer containing at least 62 percent alcohol for times when you don't have access to soap and water.
• Get tested. If you have a skin infection that requires treatment, ask your doctor to test for MRSA. Many doctors prescribe drugs that aren't effective against antibiotic-resistant staph, which delays treatment and creates more resistant germs. If you're having surgery, ask to be tested for MRSA one week before you enter the hospital.

 

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