Community‐Adapted Methicillin‐ResistantStaphylococcus aureus(MRSA): Population Dynamics of an Expanding Community Reservoir of MRSA

Abstract

To define methicillin-resistant Staphylococcus aureus (MRSA) reservoirs in the community and their population dynamics, we studied the molecular epidemiology of a random sample (n=490) from a collection of 2154 inpatient and outpatient MRSA isolates during a 7-year period in San Francisco. We noted a progressive replacement of type II staphylococcal chromosomal cassette (SCC)mec-bearing isolates with type IV SCCmec-bearing isolates, which coincided with >4-fold increase in methicillin resistance between 1998 and 2002. Type IV SCCmec-bearing isolates involved in the increase in methicillin resistance belonged to 4 molecular genotypes. These 4 genotypes were associated predominantly with community-onset disease, rather than hospital- or long-term-care facility-onset disease (76.9% vs. 19.4% vs. 3.7%; P=.0005), suggesting that they are not feral descendants of hospital isolates. The longitudinal results linked the dramatic increase in MRSA infections to an expanding community reservoir of MRSA genotypes with intrinsic community survival advantage.

Clinical significance of methicillin-resistantStaphylococcus aureuscolonization in residents in community long-term-care facilities in Spain

“…Several studies have highlighted the relevance of this epidemiological aspect which might influence the infection control practices implemented by acutecare hospitals [18][19][20][21][22] but there are limited data on the relationship of MRSA colonization and the development of infection in residents of LTCFs [12,14]. This aspect has usually been assessed in settings where patients are at great risk of MRSA infection, such as intensive care units [10].…”

Emergence of SCCmec Type IV as the Most Common Type of Methicillin-Resistant Staphylococcus aureus in a University Hospital

“…In contrast to HA-MRSA, CA-MRSA infections typically occur in young, athletic and healthy individuals without exposure to healthcare institutions [13].…”

Molecular tracing of the emergence, adaptation, and transmission of hospital-associated methicillin-resistant Staphylococcus aureus

“…In contrast to phage type 80/ 81 and SWP, the EMRSA-16 (ST36) clone appears to be restricted to the hospital setting and has reduced virulence due in part to low levels of expression of cytolytic toxins (12). Along with the EMRSA-15 (ST22) clone, EMRSA-16 has been endemic in UK hospitals for over 20 y and has also been reported less commonly in other European countries, Southeast Asia, South Africa, Australia, and North America (3,(13)(14)(15)(16)(17). The high rate of MRSA infections and the rapid spread of HA-MRSA between UK hospitals led the UK government to introduce stringent infection control legislation from 2003, resulting in a decrease in rates of nosocomial MRSA infection (18,19).…”