MRSA strains crossing borders: US CA-MRSA to Italy

Swine flu continues to dominate the headlines, but other pathogens don't read the papers. Case in point: New news about a US community strain being found and treated in a woman in Italy — better treated, as it turns out, than she was in California, where she was infected.

In a new letter in Emerging Infectious Diseases (a free journal published online and in print by the CDC — it's your tax dollars at work, just read it, already), Carla Vignaroli, Pietro E. Varaldo, and Alessandro Camporese of the Polytechnic University of Marche in Ancona amd the Santa Maria degli Angeli Regional Hospital, Pordenone report the case of

a 36-year-old Italian woman (who) was seen at Pordenone Hospital (northeastern Italy) for spider-bite–like skin lesions on the face, characterized by rapid evolution to furuncles and small abscesses. The infection had started ≈1 month earlier in California, where she had spent several months on business (wine import-export), and where she had been treated empirically with amoxicillin/clavulanate for 10 days (1 g, 3×/day), with no clinical improvement.

(At this point, I know every clinician reader and everyone who has had a MRSA skin infection is shaking his or her head. Surely by now the knowledge that "spider bite" is practically diagnostic for CA-MRSA has penetrated? But apparently not, since she was given amoxicillin/clavanulate, AKA Augmentin, which is partially penicillin-based.)

When the woman's lesions were cultured, they turned out to be caused by USA400, the original community strain, which back in the 1990s was known as MW2. That's interesting, especially in California, since USA300 has become such a dominant strain. Nevertheless, the key point is that USA400, as with USA300, has barely been recorded in Italy:

All 3 previously reported cases of CA-MRSA infection in Italy were caused by type IV SCCmec, PVL-positive strains, none of which, however, belonged to the ST80 clonal lineage that predominates in Europe (7). The first case (in 2005) was a necrotizing pneumonia caused by an ST30 isolate; the 2 other cases (2006) were severe invasive sepsis and a neck abscess, both caused by ST8 (USA300) isolates.

The concern, of course, is that once imported, they will not remain rare:

The case we note here documents the importation of a US pathogen into a country in Europe, from an area where the pathogen is widespread and has been highly virulent since the late 1990s, to an area where its penetration in the past has been poor.

The cite is: Vignaroli C, Varaldo PE, Camporese A. Methicillin-resistant Staphylococcus aureus USA400 clone, Italy [letter]. Emerg Infect Dis. 2009 Jun; [Epub ahead of print]. DOI: 10.3201/eid1506.081632