What is the utility of nasal screen for methicillin-resistant Staphylococcus aureus (MRSA) in patients with skin and soft tissue infections?

In patients at high risk of MRSA infection (eg, prior history of MRSA colonization or infection, recent hospitalization/antibiotics, intravenous drug use, traumatic injury),1 particularly in the presence of an open wound or purulent drainage, a negative MRSA nasal screen does not rule out MRSA skin and soft tissue infection (SSTI), nor does a positive MRSA nasal screen reliably predict MRSA SSTI. In contrast, in low risk patients without severe disease, a negative MRSA nasal screen may be helpful in deescalating empiric anti-MRSA coverage.

The sensitivity of MRSA nasal screen by culture or PCR for SSTIs may be as low as 40%, higher among those with an ulcer (70%), with negative predictive values of 80% to 98% depending on the prevalence of MRSA in the population; its specificity is better (72% to 96%) with positive predictive values of 7% to 76%. 2

In a retrospective study involving 57 diabetic patients hospitalized with foot wound infection, the sensitivity of MRSA nasal screen was only ~40% with a negative predictive value of 80%. 3 Another study found a negative predictive value of ~90% for MRSA nasal screen among patients with a diabetic foot infection when MRSA isolation from wounds was uncommon (7.5%).4

Several reasons explain why patients with a negative MRSA nasal screen could still have MRSA SSTI, including colonization in other body sites known to harbor MRSA (eg, rectum, axilla, groin, oropharynx) 6-9 or direct wound contamination with MRSA in the absence of carriage, particularly in healthcare facilities.10

Bonus Pearl: Did you know that dogs, particularly those owned by healthcare workers, may also carry MRSA in their nostrils?.11,12


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  1. Stevens DL, Bisno AL, Chambers H, et al. Practice guidelines for the diagnosis and treatment of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis 2014; 59:e10-52. https://www.idsociety.org/practice-guideline/skin-and-soft-tissue-infections/
  2. Carr AL, Daley MJ, Merkel KG, et al. Clinical utility of methicillin-resistant Staphylococcus aureus nasal screening for antimicrobial stewardship: A review of current literature. Pharmacotherapy 2018;38:1216-1228. https://accpjournals.onlinelibrary.wiley.com/doi/abs/10.1002/phar.2188
  3. Lavery LA, La Fonatine J, Bhavan K, et al. Risk factors for methicillin-resistant Staphylococcus aureus in diabetic foot infections. Diabet Foot Ankle 2014;5:10.3402/dfa.v5.23575. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3984406/
  4. Mergenhagen KA, Croix M, Starr KE, et al. Utility of methicillin-resistant Staphylococcus aureus nares screening for patients with a diabetic foot infection. Antimicrob Agents Chemother 2020;64:e02213-19. https://pubmed.ncbi.nlm.nih.gov/31988097/  
  5. Currie A, Davis L, Odrobina E, et al. Sensitivities of nasal and rectal swabs for detection of methicillin-resistant Staphylococcus aureus colonization in an active surveillance program. J Clin Microbiol 2008;46:3101-3103. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2546770/
  6. Mermel LA, Cartony JM, Covington P, et al. Methicillin-resistant Staphylococcus aureus colonization at different body sites: a prospective, quantitative analysis. J Clin Microbiol 2011;49:1119-21. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3067701/#B4
  7. Baker SE, Brecher SM, Robillar E, et al. Extranasal methicillin-resistant Staphylococcus aureus colonization at admission to an acute care Veterans Affairs Hospital. Infect Control Hosp Epidemiol 2010;31:42-6. https://pubmed.ncbi.nlm.nih.gov/19954335/
  8. Manian FA, Senkel D, Zack J et al. Routine screening for methicillin-resistant Staphylococcus aureus among patients newly admitted to an acute rehabilitation unit. Infect Control Hosp Epidemiol 2002;23:516-9. https://pubmed.ncbi.nlm.nih.gov/12269449/
  9. Lautenbach E, Nachamkin I, Hu B, et al. Surveillance culture for detection of methicillin-resistant Staphylococcus aureus: diagnostic yield of anatomic sites and comparison of provider- and patient-collected samples. Infect Control Hosp Epidemiol 2009;30:380-82. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2665909/
  10. Boyce JM, Bynoe-Potter G, Chenevert C, et al. Environmental contamination due to methicillin-resistant Staphylococcus aureus: possible infection control implications 1997;18:622-7. https://pubmed.ncbi.nlm.nih.gov/9309433/  
  11. Boost MV, O’donaghue MM, James A. Prevalence of Staphylococcus aureus among dogs and their owners. Epidemiol Infect 2008;136:953-64. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870875/#ref017
  12. Manian FA. Asymptomatic carriage of mupirocin-resistant methicillin-resistant Staphylococcus aureus (MRSA) in a pet dog associated with MRSA infection in household contacts. Clin Infect Dis 2003;36;e26-28. https://academic.oup.com/cid/article/36/2/e26/317343



Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

What is the utility of nasal screen for methicillin-resistant Staphylococcus aureus (MRSA) in patients with skin and soft tissue infections?

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