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Original Article
Risk factors for amendment in type, duration and setting of prescribed outpatient parenteral antimicrobial therapy (OPAT) for adult patients with cellulitis: a retrospective cohort study and CART analysis
  1. Michael Quirke1,
  2. Emma May Curran2,
  3. Patrick O’Kelly3,
  4. Ruth Moran4,
  5. Eimear Daly4,
  6. Seamus Aylward4,
  7. Gerry McElvaney2,
  8. Abel Wakai1,5
  1. 1Emergency Care Research Unit (ECRU),Royal College of Surgeons Ireland (RCSI), Dublin, Ireland
  2. 2Department of Medicine, RCSI, Beaumont Hospital, Dublin, Ireland
  3. 3Department of Statistics, Renal Medicine Unit,Beaumont Hospital, Dublin, Ireland
  4. 4VHI Homecare, Waverly Business Park, Dublin, Ireland
  5. 5Department of Emergency Medicine, Beaumont Hospital, Dublin, Ireland
  1. Correspondence to Dr Abel Wakai, Emergency Care Research Unit (ECRU), Division of Population Health Sciences, RCSI, Stephen's Green, Dublin, Ireland; awakai{at}


Purpose of the study To measure the percentage rate and risk factors for amendment in the type, duration and setting of outpatient parenteral antimicrobial therapy (OPAT) for the treatment of cellulitis.

Study design A retrospective cohort study of adult patients receiving OPAT for cellulitis was performed. Treatment amendment (TA) was defined as hospital admission or change in antibiotic therapy in order to achieve clinical response. Multivariable logistic regression (MVLR) and classification and regression tree (CART) analysis were performed.

Results There were 307 patients enrolled. TA occurred in 36 patients (11.7%). Significant risk factors for TA on MVLR were increased age, increased Numerical Pain Scale Score (NPSS) and immunocompromise. The median OPAT duration was 7 days. Increased age, heart rate and C reactive protein were associated with treatment prolongation. CART analysis selected age <64.5 years, female gender and NPSS <2.5 in the final model, generating a low-sensitivity (27.8%), high-specificity (97.1%) decision tree.

Conclusions Increased age, NPSS and immunocompromise were associated with OPAT amendment. These identified risk factors can be used to support an evidence-based approach to patient selection for OPAT in cellulitis. The CART algorithm has good specificity but lacks sensitivity and is shown to be inferior in this study to logistic regression modelling.

  • Treatment failure

Statistics from


  • Contributors MQ, GM and AW conceived of the study. POK led statistical design and data analysis. EMC led data collection with MQ, RM, ED and SA all participating. EMC and MQ led case report form design and data presentation for analysis. MQ led the drafting of the manuscript, and all other authors participated in editing the manuscript, had final approval over the text and take responsibility for the content.

  • Funding EMC was supported by a Research Summer School Grant from the Royal College of Surgeons in Ireland.

  • Competing interests GME is the Clinical Director of Vhi Homecare Ireland. SA, ED and RM are employees of Vhi Homecare Ireland. All the other authors have no conflict of interest.

  • Ethics approval Beaumont Hospital Research Ethics Committee.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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