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Transmissibility of Livestock-associated Methicillin-Resistant Staphylococcus aureus - Vol. 19 No. 11 - November 2013 - Emerging Infectious Disease journal - CDC
Transmissibility of Livestock-associated Methicillin-Resistant Staphylococcus aureus
David J. Hetem

, Martin C.J. Bootsma, Annet Troelstra, and Marc J.M. Bonten
Author affiliations: University Medical Center Utrecht, Utrecht, the Netherlands (D.J. Hetem, M.C.J. Bootsma, A. Troelstra, M.J.M. Bonten); University of Utrecht, Utrecht (M.C.J. Bootsma)
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Abstract
Previous findings have suggested that the nosocomial transmission capacity of livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) is lower than that of other MRSA genotypes. We therefore performed a 6-month (June 1–November 30, 2011) nationwide study to quantify the single-admission reproduction number, RA, for LA-MRSA in 62 hospitals in the Netherlands and to compare this transmission capacity to previous estimates. We used spa typing for genotyping. Quantification of RA was based on a mathematical model incorporating outbreak sizes, detection rates, and length of hospital stay. There were 141 index cases, 40 (28%) of which were LA-MRSA. Contact screening of 2,101 patients and 7,260 health care workers identified 18 outbreaks (2 LA-MRSA) and 47 secondary cases (3 LA-MRSA). RA values indicated that transmissibility of LA-MRSA is 4.4 times lower than that of other MRSA (not associated with livestock).Methicillin-resistant
Staphylococcus aureus (MRSA) is one of the leading causes of nosocomial infections and leads to considerable illness, death, and health care costs (
1,2). The worldwide epidemiology of MRSA has changed as MRSA originating in the community has increased. These community-associated MRSA (CA-MRSA) strains are replacing their hospital-associated counterparts in hospitals in the United States; the major dominant clone is MRSA strain USA300 (
3). In recent years, another MRSA clone, which originated in the community and is associated with exposure to livestock, has emerged in different countries worldwide, including the United States (
4,5). Even more worrying, countries with a historically low prevalence of MRSA, like the Netherlands and Denmark, have seen an increase in livestock-associated MRSA (LA-MRSA), belonging to clonal complex 398 (
5). In the Netherlands, LA-MRSA accounted for 39% of all new MRSA isolated in 2011 (
6). Yet almost all isolates have been detected through screening, and in 2009, nine infections were caused by MRSA sequence type 398 (
7). Invasive infections caused by LA-MRSA include endocarditis, osteomyelitis, and ventilator-associated pneumonia (
8,9).
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