Staphylococcus aureus Skin and Soft Tissue Infection Recurrence Rates in Outpatients: A Retrospective Database Study at 3 US Medical Centers

Abstract

Background: Staphylococcus aureus skin and soft tissue infections (SA-SSTIs) are common in healthcare and community settings, and recurrences occur at variable frequency, even after successful initial treatment. Knowing the exact burden and timing of recurrent disease is critical to planning and evaluating interventions to prevent recurrent SSTIs.

Methods: In this retrospective study, SSTI cases in patients aged ≥18 years at 3 US medical centers (Columbia, Chicago, Vanderbilt) between 2006 and 2016 were analyzed according to a biennial cohort design. Index SSTIs (with or without key comorbidities), either microbiologically confirmed to be SA-SSTI or not microbiologically tested (NMT-SSTI), were recorded within 1 calendar year and followed up for 12 months for recurrent infections. The number of index cases, proportion of index cases with ≥1 recurrence(s), time to first recurrence, and number of recurrences were collected for both SA-SSTI and NMT-SSTI events.

Results: In the most recent cohorts, 4755 SSTI cases were reported at Columbia, 2873 at Chicago, and 6433 at Vanderbilt. Of these, 452, 153, and 354 cases were confirmed to be due to S. aureus. Most cases were reported in patients without key comorbidities. Across centers, 16.4%-19.0% (SA-SSTI) and 11.0%-19.2% (NMT-SSTI) of index cases had ≥1 recurrence(s). In patients without key comorbidities, more than 60% of index SSTIs with recurrences had only 1 recurrence, half of which occurred in the first 3 months following primary infection.

Conclusions: SA-SSTI recurrences are common among healthy adults and occur in at least 1 in 6 individuals during the 1 year following the primary event.

Keywords: Staphylococcus aureus; SSTI recurrence; antimicrobial resistance; methicillin-resistant Staphylococcus aureus; skin and soft tissue infection (SSTI).

Figure 1.

Plain language summary of the outcomes of the study. Purple human, human with Staphylococcus aureus infection; dark rose human, human with comorbidities; light rose human, human without comorbidities; half dark rose/purple human, human with S. aureus infection and comorbidities; half light rose/purple human, human with S. aureus infection and without comorbidities; gray human, general population. Abbreviations: N, total number of cases; SSTI, skin and soft tissue infection. SSTI Icon taken and modified from Servier Medical Art (https://smart.servier.com/image-set-download/), licensed under a Creative Commons Attribution 3.0 France. Hourglass and medical record icons made by Flat Icons and Freepik, respectively, from www.flaticon.com.

Figure 2.

Overview of study design and SSTI cases reported by cohorts. Abbreviations: i, index case; NMT-SSTI, skin and soft tissue infection not microbiologically tested; non SA-SSTI, SSTI cultured and confirmed negative for Staphylococcus aureus; P, patient; SA-SSTI, skin and soft tissue infection cultured and confirmed positive for S. aureus; x, recurrence.

Figure 3.

Sample characteristics. Abbreviations: HIV, human immunodeficiency virus; SA-SSTI, skin and soft tissue infection caused by Staphylococcus aureus; NMT-SSTI, skin and soft tissue infection not microbiologically tested; SD, standard deviation. People and malignant cells Icons taken and modified from Servier Medical Art (https://smart.servier.com/image-set-download/), licensed under a Creative Commons Attribution 3.0 France.

Figure 4.

Recurrence rate of skin and soft tissue infections (SSTIs) within 12 months following the index SSTI in each evaluable cohort. Evaluable cohorts with >100 SA-SSTI cases are bolded. Abbreviations: %, proportion of cases with at least 1 recurrence; CI, confidence interval; NMT-SSTI, skin and soft tissue infection not microbiologically tested; SA-SSTI, skin and soft tissue infection caused by Staphylococcus aureus; N, total number of cases.

Figure 5.

Incidence proportion of skin and soft tissue infections (SSTIs) caused by Staphylococcus aureus (A) and SSTIs not microbiologically tested (B) with at least 1 recurrent event in the most recent evaluable cohorts. Error bars represent 95% confidence intervals. Key comorbidities: complicated diabetes, hemodialysis, human immunodeficiency virus/AIDS, and malignant neoplasia.

Figure 6.

Cumulative recurrence rates for SA-SSTI cases (A) and NMT-SSTI cases (B) without key comorbidities in the most recent evaluable cohorts. Abbreviations: NMT-SSTI, skin and soft tissue infection not microbiologically tested; SA-SSTI, skin and soft tissue infection caused by Staphylococcus aureus.

Figure 7.

Proportional distribution in number of recurrences for SSTI cases without key comorbidities in the most recent evaluable cohorts. Abbreviations: NMT-SSTI, skin and soft tissue infection not microbiologically tested; SA-SSTI, skin and soft tissue infection caused by Staphylococcus aureus.

Figure 8.

Distribution of mono- and polymicrobial SA-SSTI cases in the most recent evaluable cohorts. Percentages were calculated using the total number of cases in each category as the denominator. Abbreviations: MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-susceptible S. aureus; N, total number of cases; n (%), number and percentage of cases in each category; SA-SSTI, skin and soft tissue infection caused by S. aureus.