MRSA bloodstream infections among injecting drug users

Background Bloodstream infections (BSIs) caused by methicillin-resistant Staphylococcus aureus (MRSA) has increased among injecting drug users (IDU) in Helsinki-Uusimaa Healthcare District (HUS), Southwest Finland (VSSHP) and Pirkanmaa. Our aim was to investigate the extent of the outbreak, MRSA strains involved and the severity of these infections.

Methods Background information of BSI cases caused by MRSA among IDUs during 2015-2022 were collected from the regional MRSA registers of HUS, VSSHP and Pirkanmaa. Other healthcare districts were asked whether MRSA BSIs were detected among IDUs during 2019-2022.Spa-typing and whole-genome sequencing was conducted to MRSA strains in THL's expert microbiology laboratory.

Results In HUS, MRSA BSI cases among IDUs doubled during 2020-2021. Of the cases, 70% were caused by two different pvl-gene positive MRSA-strains (spa-type t008 and t024). In VSSHP, the most common spa-type was t386 and in Pirkanmaa t304.

Conclusions The increase in severe MRSA infections among IDUs was partly explained by the spread of certain MRSA strains that can cause invasive infections more frequently.

Laura Pakarinen, Laura Lindholm, Mari Kanerva, Reetta Huttunen, Minna Nieminen, Anu Harttio-Nohteri, Tiina Kurvinen, Jaana-Marija Lehtinen, Outi Lyytikäinen