Community-associated methicillin-resistant Staphylococcus aureus, Iowa, USA

Area of Science:

• Microbiology
• Infectious Diseases
• Epidemiology

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant public health threat.
• Surveillance of invasive MRSA infections is crucial for understanding evolving epidemiology.
• Specific MRSA strains, like USA300 and USA400, have emerged as important causes of infection.

Purpose of the Study:

• To analyze antimicrobial susceptibility and molecular types of invasive MRSA isolates in Iowa from 1999-2006.
• To track the prevalence of specific MRSA strains (USA300, USA400) over time.
• To identify risk factors and seasonality associated with invasive community-associated (CA)-MRSA infections.

Main Methods:

• Antimicrobial drug susceptibility testing was performed on 1,666 invasive MRSA isolates.
• Molecular typing was used to identify MRSA strains, focusing on USA300 and USA400.
• Statistical analysis was conducted to assess trends, seasonality, and risk factors for CA-MRSA infections.

Main Results:

• USA300 and USA400 isolates demonstrated resistance to at least three non-beta-lactam antimicrobial drug classes.
• The proportion of invasive MRSA isolates identified as USA300 or USA400 significantly increased from 1999-2005 to 2006 (p<0.0001).
• Invasive CA-MRSA infections in 2006 peaked during the summer (p = 0.0004). Age under 69 was linked to increased risk (OR 5.1), while hospital exposure showed a decreased risk (OR 0.07).

Conclusions:

• The study highlights the increasing dominance of USA300 and USA400 strains in invasive MRSA infections in Iowa.
• Community-associated MRSA infections exhibit seasonal patterns and are more prevalent in younger individuals.
• These findings underscore the importance of ongoing surveillance and strain characterization for effective MRSA control strategies.