Can you tell me about oxadillan staphylococcus infection, its causes, treatment and complications? Also, how is it generally contracted? Is it contagious from person to person, or airborne?

E.J.

Staphylococcus aureus (S. aureus) is among the most common disease-causing bacteria in humans. Virtually everyone will develop a staph infection at some point, usually without serious consequences. Staph is also sometimes responsible for serious infections. I assume what you are referring to is oxacillin-resistant S. aureus (ORSA). Oxacillin (Bactocill) is an antibiotic in the penicillin family, and ORSA refers to strains of S. aureus that are resistant to this drug, meaning that they are not very susceptible to the medication's effects.

Most frequently, staph causes skin infections, such as impetigo and folliculitis. Both of these conditions require only local treatment, namely hot compresses soaked in saline (salt solution) or topical antibiotics. Staph also is the usual cause of furuncles, or boils, larger skin infections that sometimes require the doctor to cut them open with to allow the pus to drain out. When several furuncles coalesce (become interconnected), a carbuncle is formed. This type of infection can also be cured surgically, but the procedure is somewhat more invasive.

Less commonly, staph bacteria invade the lung or the bloodstream and cause life-threatening infections. Staph usually enter the bloodstream through the skin, spreading from a skin infection or through a break in the skin. In hospital patients, the organisms also may gain entry into the blood through an intravenous (IV) catheter (a tube inserted into the patient's vein to deliver blood, fluids, drugs or other substances). The bacteria then can spread to the heart, causing endocarditis, an infection of the heart valves; to the bone, causing a serious infection called osteomyelitis; or to the lung, causing pneumonia and abscesses in the lung tissue.

Staph is not contagious in the usual sense, however. We all periodically have staph on our skin and even in our noses, and most staph infections come from bacteria that have "colonized" us for some time. If you have contact with a person with impetigo, you could pick up their staph and develop an infection. But such contact will not automatically cause you to develop a bloodstream infection, so being around a patient with this problem is usually not a major concern.

Many years ago, nearly all strains of staph could be killed by penicillin. But staph bacteria soon became resistant to the drug, and researchers created synthetic forms of penicillin such as oxacillin and methicillin to treat staph infections. In the 1970s, however, some S. aureusstrains developed resistance to all of the penicillins. Because laboratories routinely use methicillin to identify resistance to drugs in the penicillin family, these resistant strains were named MRSA for methicillin-resistant Staphylococcus aureus. It became necessary to use vancomycin (Vancocin), an antibiotic that is unrelated to penicillin, to treat such infections. In the last few years, over half of all staph infections of patients in some hospitals are MRSA, narrowing the treatment options. Also, there are now strains that are at least relatively resistant even to vancomycin.

It is thus very important to prevent the spread of drug-resistant strains among patients in the hospital, most of whom have intravenous catheters in place and are susceptible to developing staph infections. Outside of the hospital, however, most S. aureus strains are still vulnerable to penicillins. Since serious infections acquired outside the hospital are relatively uncommon, MRSA is not the type of infection most of us have to worry about. It is not spread by airborne routes, and even if you become colonized with a resistant strain, the chance of your developing a serious infection is rather low.