Although hospital superbugs like MRSA - methicillin resistant Staphylococcus aureus - are now a widespread and recognised problem, new MRSA strains that have emerged and are spreading amongst the wider public in the USA may pose a bigger threat, according to Exeter researchers speaking (Wednesday 28 November 2007) at the Federation of Infection Societies Conference 2007 at the University of Cardiff, UK, which runs from 28-30 November 2007.
“The new community associated MRSA strains appear to be more virulent and more easily spread between people”, says Dr Marina Morgan from the Royal Devon & Exeter Foundation NHS Trust. “These community associated versions have been found in people with few, if any, reasons to have MRSA. Typically they haven't recently been in hospital, or and are not looking after or living with people with MRSA.”
Although more antibiotics are still effective against community MRSA than against the hospital MRSA, the community associated infections are often more virulent. Most can also produce a toxin called Panton-Valentine leucocidin, or PVL, that kills white blood cells – our bodies' key defence against invasive bacteria.
“Although the resistant strain is not yet widespread in the UK, we have seen increasing numbers of PVL- toxin producing Staphylococcus aureus infections, mainly presenting with recurrent boils and abscesses. This excessive production of white cells to compensate for those killed by the PVL toxin leads to recurrent severe boils and abscesses. The MRSA is easily spread by close contact, such as in families, nurseries and athletic teams”, says Dr Morgan. “These new strains of bacteria appear to be able to stick to damaged skin and airways better than hospital MRSA strains, and they also multiply at a faster rate.
A minority of patients carrying these PVL-producing staphylococci can suffer severe invasive infections such as septicaemia or a lethal form of pneumonia where the lung tissue itself is destroyed by the toxins. With this type of necrotising PVL pneumonia, even with the strongest antibiotics, more than 60% of otherwise healthy young and fit people will die”.
So far community associated MRSA strains are mainly spreading in America, where they are a major cause of infection in children. Whilst doctors do not know if the bacteria could spread as rapidly in the UK, they are already worried. These new strains of bacteria appear to be able to stick to damaged skin and airways better than hospital MRSA strains, and they also multiply at a faster rate.
“These infections are easily missed clinically, where they can be dismissed as just recurrent boils and overlooked until a serious infection develops”, says Dr Morgan. “Then, with severe invasive infections like pneumonia, early diagnosis is vital as treatment with the correct antibiotics and massive doses of immunoglobulin can save children's lives”.
If the community associated MRSA strains take hold and spread in the UK as they have in the USA then many more patients with unsuspected MRSA will be admitted to hospitals, given the wrong antibiotics, and when doctors finally realise the infection is MRSA, by the time patients get the correct treatment it may be too late.