Demographic characteristics of hospital-acquired (HA-)MRSA infections differ from those of CA-MRSA, the former occurring mainly in elderly people and the latter occurring in young people. HA-MRSA infections are particularly associated with surgical wounds or intravenous indwelling catheters. CA-MRSA infections are mainly primary skin and soft tissue infections occurring in patients with no initial skin wounds. The Panton-Valentine leukocidin (PVL) produced by CA-MRSA strains all over the world represents, with its necrotic activity, one of the virulence factors possibly associated with cutaneous tissue destruction. The necrotic activity of PVL seems to be the major factor behind dramatic cases of necrotising pneumonia, leading to a massive alveolar septa destruction; the mortality rate is 75%.

These PVL-positive CA-MRSA are easily transmissible not only within families but also on a larger scale in community settings such as prisons, schools and sport teams. Skin-to-skin contact involving no abrasion and indirect contact with contaminated objects such as towels, sheets, sport equipment seem to represent the mode of transmission. The skin infection often has the initial appearance of an insect bite. In the US, infected prisoners were thought to have been bitten by spiders, and in our institution, a skillful technicians who had been working for several years with PVL positive CA-MRSA thought she had been bitten by a mosquito before developing a large forearm skin abscess which required surgical treatment. The exact prevalence of CA-MRSA is still unknown, as the isolated strains have mainly been taken from patients requiring admission to hospital. These isolates collected at hospitals certainly represent the tip of the iceberg of the entire population of the CA-RSA spreading in each continent. The most prevalent clone of CA-MRSA strains, assigned to the multilocus sequence type 0 (ST 80), have been detected in several European countries, demonstrating its epidemicpotential.. It has been detected in rance, Switzerland, Germany, Greece and also the Nordic countries that were initially protected rom the HA-MRSA invasion. Another clone (ST30), initially described in Australasia is reported in this issue of Eurosurveillance to have spread both in the Netherlands and in Latvia [1,2], demonstrating the intercontinental spread of this clone. Similarly the ST8 and ST59 clones, initially described in the US, have been reported in the Netherlands by Wannet et al [2]. The small-sized SCCmec type IV element uniformly present in CA-MRSA reported so far is no longer a universal feature of CA-MRSA, as Wannet et al report the presence of SCCmec type I and III in some of their strains.

Although MRSA has been described for decades in hospital settings, these strains never previously appeared to represent a threat to the community. Currently, the threat appears to be that strains that first emerged in the community will spread further within the community, and may potentially spread to hospitals too [1]. Will all S. aureus strains progressively become resistant to methicillin?

The first priority is to set up and implement adequate prevention measures to reduce or limit the spreading of these strains. In past outbreaks when cases of skin and soft tissue infections have been observed in a close-living community of patients, conventional therapeutic and infection control measures have proven successful in curing the infected patients and controlling the outbreak. The main question now is how to prevent transmission of these strains in the open community.