USA300 Methicillin-Resistant Staphylococcus aureus, United States, 2000-2013

Abstract

In the United States, methicillin-resistant Staphylococcus aureus (MRSA) with the USA300 pulsed-field gel electrophoresis type causes most community-associated MRSA infections and is an increasingly common cause of health care-associated MRSA infections. USA300 probably emerged during the early 1990s. To assess the spatiotemporal diffusion of USA300 MRSA and USA100 MRSA throughout the United States, we systematically reviewed 354 articles for data on 33,543 isolates, of which 8,092 were classified as USA300 and 2,595 as USA100. Using the biomedical literature as a proxy for USA300 prevalence among genotyped MRSA samples, we found that USA300 was isolated during 2000 in several states, including California, Texas, and midwestern states. The geographic mean center of USA300 MRSA then shifted eastward from 2000 to 2013. Analyzing genotyping studies enabled us to track the emergence of a new, successful MRSA type in space and time across the country.

Keywords: MRSA; Methicillin-resistant Staphylococcus aureus; USA300; United States; antimicrobial resistance; bacteria; spatiotemporal analysis; systematic review.

Figure 1

The most frequently reported spa types (A) and multilocus sequence types (B) for methicillin-resistant Staphylococcus aureus isolates obtained in 2000–2004, 2005–2009, and 2010–2013, United States.

Figure 2

Proportions of methicillin-resistant Staphylococcus aureus isolates, United States 2000–2013. A) USA300 strain type. B) USA100 strain type. Darker shading indicates higher proportions of types reported in studies conducted during those years.

Figure 3

Proportions of methicillin-resistant Staphylococcus aureus isolates in each state that were defined as USA300, USA100, or other strain types, United States 2000–2013.

Figure 4

Weighted mean geographic center for proportions of methicillin-resistant Staphylococcus aureus (MRSA) USA300 strain type, United States, 2000–2013. This map shows the likely trend in the spread of USA300 as a proportion of all MRSA isolates that underwent genotyping, but the trajectory could be biased by large studies or lack of studies in certain states in specific years. The final mean center for 2012–2013 is represented differently to indicate that it is based on a small number of isolates.

Figure 5

Proportion of methicillin-resistant Staphylococcus aureus USA300 and USA100 strain types and total sample size in 4 Census regions, United States 2000–2013. A) West. B) Midwest. C) Northeast. D) South. Linear regression lines are fit for each type. Solid line, USA300; dashed line, USA100.