Increasing trend of antimicrobial resistance among methicillin-resistant Staphylococcus aureus strains in Southwest Finland, 2007–2016: An analysis of shifting strain dynamics and emerging risk factors

Abstract

Objective

Substantial rise in the annual incidence of methicillin-resistant Staphylococcus aureus (MRSA) was reported in Southwest Finland (12.4–24.9/100,000 people) between 2007 and 2016. To understand the implications of these changes to the management of MRSA, we sought to analyse the antimicrobial resistance (AMR) trends of MRSA in relation with patient characteristics.

Methods

Antimicrobial susceptibility was determined for 10 clinically relevant antimicrobials. Strains with resistance to ≥2 antimicrobials were defined multi-resistant. The isolates were spa-typed and clustered. AMR trends and risk factors were identified by associating resistant phenotypes with patient demographics.

Results

A total of 983 new MRSA cases were identified between 2007 and 2016. After 2011, significant increasing trends were observed in the proportion of isolates resistant to clindamycin (13.9%–31.5%, P < 0.001), erythromycin (19.4%–35.4%, P < 0.001) and tetracycline (16.7%–32%, P < 0.001). The proportion of multi-resistant isolates more than doubled from 14.8% to 39.2%. The increasing AMR trend was reflected in the increase of new strain types and the decrease of previously dominant, non-multi-resistant strains. Patient risk factors associated with (P < 0.001) the acquisition of multi-resistant strains included community acquisition, livestock contact, hospital care abroad and immigrant status.

Conclusions

Notable increasing AMR trends among MRSA isolates were observed in Southwest Finland, 2007–2016. The shift in patient demographics to younger age groups and community acquisition contributed to the increase in multi-resistant strains. Immigration, contact with hospital environment abroad and contact with livestock were identified as essential risk factors of multi-resistance. The increased level of co-resistance has persisted after 2016.