Drug-resistant MRSA bacteria: Here to stay in both hospital and community

The pre­dic­tion that both strains will coex­ist is reas­sur­ing because pre­vi­ous pro­jec­tions indi­cated that the more inva­sive and fast-growing com­mu­nity strains would over­take and elim­i­nate hos­pi­tal strains, pos­si­bly pos­ing a threat to pub­lic health.

Researchers at Prince­ton Uni­ver­sity used math­e­mat­i­cal mod­els to explore what will hap­pen to com­mu­nity and hos­pi­tal MRSA strains, which dif­fer genet­i­cally. Orig­i­nally MRSA, which is short for methicillin-resistant Staphy­lo­coc­cus aureus, was con­fined to hos­pi­tals. How­ever, community-associated strains emerged in the past decade and can spread widely from per­son to per­son in schools, ath­letic facil­i­ties and homes.

Both com­mu­nity and hos­pi­tal strains cause dis­eases rang­ing from skin and soft-tissue infec­tions to pneu­mo­nia and sep­ticemia. Hos­pi­tal MRSA is resis­tant to numer­ous antibi­otics and is very dif­fi­cult to treat, while com­mu­nity MRSA is resis­tant to fewer antibiotics.

The new study found that these dif­fer­ences in antibi­otic resis­tance, com­bined with more aggres­sive antibi­otic usage pat­terns in hos­pi­tals ver­sus the com­mu­nity set­ting, over time will per­mit hos­pi­tal strains to sur­vive despite the com­pe­ti­tion from com­mu­nity strains. Hospital-based antibi­otic usage is likely to suc­cess­fully treat patients infected with com­mu­nity strains, pre­vent­ing the new­comer strains from spread­ing to new patients and gain­ing the foothold they need to out-compete the hos­pi­tal strains.

The researchers made their pre­dic­tions by using math­e­mat­i­cal mod­els of MRSA trans­mis­sion that take into account data on drug-usage, resis­tance pro­files, person-to-person con­tact, and patient age.

Pub­lished Feb­ru­ary 28 in the jour­nal PLOS Pathogens, the study was con­ducted by post­doc­toral researcher Roger Kouyos, now a scholar at the Uni­ver­sity of Zurich, and Eili Klein, a grad­u­ate stu­dent who is now an assis­tant pro­fes­sor in the Johns Hop­kins School of Med­i­cine. They con­ducted the work under the advise­ment of Bryan Gren­fell, Princeton's Kathryn Briger and Sarah Fen­ton Pro­fes­sor of Ecol­ogy and Evo­lu­tion­ary Biol­ogy and Pub­lic Affairs at Princeton's Woodrow Wil­son School of Inter­na­tional and Pub­lic Affairs.