Profligate antibiotic use has led to the rise of drug-resistant organisms, writes Dr Muiris Houston
The most recent outbreak of an antibiotic-resistant infection in the orthopaedic unit of Our Lady's Hospital, Navan, is a reminder of an increasingly prevalent problem.
Common examples of multi- drug-resistant organisms include MRSA (methicillin resistant staph. aureus), PRSP (penicillin resistant strep. pneumoniae) and VRE (vancomycin resistant enterococcus).
MRSA and VRE are most commonly found in healthcare settings such as hospitals and nursing homes. PRSP are more common in the community.
The emergence of drug- resistant bugs threatens to reverse progress made by the discovery of penicillin and other antibiotics developed over the last 50 years. Theoretically, it poses the real possibility of a bug emerging that is untreatable by any antibiotic known to man.
Although commonly referred to as superbugs, VRE and MRSA are more accurately called resistant bugs. A superbug is a bacterium that is highly infectious whereas VRE and MRSA are extremely difficult to treat because of their resistance to a wide range of antibiotics, not just the agents vancomycin and methicillin.
The bugs, enterococcus faecalis and E. faecium, normally inhabit the gastro-intestinal tract. They also inhabit the female genital tract without causing disease.
However, in patients who are critically ill or who have had recent major surgery, they can multiply and cause urinary tract infections and wound infections that are resistant to treatment (VRE).
Until the 1980s, such infections were easily treated with an antibiotic called vancomycin. Since then, however, resistance to treatment has increased to the point where a recently introduced antibiotic, linezolid, is now being fought off by the enterococci.
The resistant form of the bug can be transmitted from person to person by means of nursing personnel and contaminated equipment. It can also be picked up from surfaces in operating theatres and wards.
Staph. aureus is a bacterium that is carried harmlessly on the skin and in the nose by 30 per cent of people. It is a common cause of skin infections.
However, people who have had a major illness or who have external lines running into them are at risk of developing a serious staph. aureus infection in the bloodstream.
Methicillin is a form of penicillin, developed to treat penicillin-resistant forms of staph. aureus. By the 1960s, however, versions of the bug that were resistant to methicillin appeared. The term methicillin resistant staph. aureus(MRSA) was coined and continues to be used to describe antibiotic resistant variants of the microbe.
How can VRE and MRSA be treated? The patient must be isolated in a side room away from others and special nursing procedures must be used. Affected areas must be deep- cleansed and treatment attempted with linezolid.
It is not all bad news. A task force in Sioux City, Iowa, succeeded in reducing the prevalence of VRE in all health- care facilities from 2.5 per cent to 0.5 per cent. It did this by screening patients on admission for the organism as well as implementing strict infection control policies and monitoring antibiotic use.
A recent paper in the British Medical Journal described how orthopaedic surgeons in Britain reduced the incidence of MRSA by ring-fencing a 28-bed unit and using it exclusively for people undergoing joint replacement surgery.
But the days of the magic bullet are definitely numbered. Because of our profligacy in using penicillin and its many successors, multi-drug-resistant infection is set to increase.
Doctors have over-prescribed antibiotics, farmers have over- used these agents and the reality of international travel means that resistant bugs arrive speedily from other continents.