Epidemiology of Surgical Site Infection in a Community Hospital Network

Baker, A.W. Infection Control & Hospital Epidemiology. 2016. 37:519–526

Objective: To describe the epidemiology of complex surgical site infection (SSI) following commonly performed surgical procedures in community hospitals and to characterize trends of SSI prevalence rates over time for MRSA and other common pathogens

Methods: We prospectively collected SSI data at 29 community hospitals in the southeastern United States from 2008 through 2012. We determined the overall prevalence rates of SSI for commonly performed procedures during this 5-year study period. For each year of the study, we then calculated prevalence rates of SSI stratified by causative organism. We created log-binomial regression models to analyze trends of SSI prevalence over time for all pathogens combined and specifically for MRSA.

Results: A total of 3,988 complex SSIs occurred following 532,694 procedures (prevalence rate, 0.7 infections per 100 procedures). SSIs occurred most frequently after small bowel surgery, peripheral vascular bypass surgery, and colon surgery. Staphylococcus aureus was the most common pathogen. The prevalence rate of SSI decreased from 0.76 infections per 100 procedures in 2008 to 0.69 infections per 100 procedures in 2012 (prevalence rate ratio [PRR], 0.90; 95% confidence interval [CI], 0.82–1.00). A more substantial decrease in MRSA SSI (PRR, 0.69; 95% CI, 0.54–0.89) was largely responsible for this overall trend.

Conclusions: The prevalence of MRSA SSI decreased from 2008 to 2012 in our network of community hospitals. This decrease in MRSA SSI prevalence led to an overall decrease in SSI prevalence over the study period.

Read the abstract here

Staphylococcus aureus dry-surface biofilms are not killed by sodium hypochlorite: implications for infection control

Almatroudi, A. et al. Journal of Hospital Infection. Published online: 12 April 2016

http://wellcomeimages.org/indexplus/result.html?_IXMAXHITS_=1&_IXACTION_=query&_IXFIRST_=15&_IXSR_=d3cciuE7ZSr&_IXSS_=_IXMAXHITS_%3d15%26_IXFPFX_%3dtemplates%252ft%26_IXFIRST_%3d1%26c%3d%2522historical%2bimages%2522%2bOR%2b%2522contemporary%2bimages%2522%2bOR%2b%2522corporate%2bimages%2522%2bOR%2b%2522contemporary%2bclinical%2bimages%2522%26%252asform%3dwellcome%252dimages%26%2524%253dsi%3dtext%26_IXACTION_%3dquery%26i_pre%3d%26IXTO%3d%26t%3d%26_IXINITSR_%3dy%26i_num%3d%26%2524%253dsort%3dsort%2bsortexpr%2bimage_sort%26w%3d%26%2524%253ds%3dstaphylococcus%2baureus%26IXFROM%3d%26_IXSUBMIT_%3dSubmit%26_IXshc%3dy%26%2524%2b%2528%2528with%2bwi_sfgu%2bis%2bY%2529%2band%2bnot%2b%2528%2522contemporary%2bclinical%2bimages%2522%2bindex%2bwi_collection%2bor%2b%2522corporate%2bimages%2522%2bindex%2bwi_collection%2529%2529%2band%2bnot%2bwith%2bsys_deleted%3d%252e%26_IXrescount%3d24&_IXSPFX_=templates%2ft&_IXFPFX_=templates%2ft
Image source: Wellcome Images // CC-BY-NC-ND 4.0

Image shows Staphylococcus aureus – macro photo x 10 of culture, characteristic gold/yellow colonies.

Background: Dry hospital environments are contaminated with pathogenic bacteria in biofilms, which suggests that current cleaning practices and disinfectants are failing.

Aim: To test the efficacy of sodium hypochlorite solution against Staphylococcus aureus dry-surface biofilms.

Methods: The Centers for Disease Control and Prevention Biofilm Reactor was adapted to create a dry-surface biofilm, containing 1.36×107 S. aureus/coupon, by alternating cycles of growth and dehydration over 12 days. Biofilm was detected qualitatively using live/dead stain confocal laser scanning microscopy (CLSM), and quantitatively with sonicated viable plate counts and crystal violet assay. Sodium hypochlorite (1000 to 20,000 parts per million) was applied to the dry-surface biofilm for 10 min, coupons were rinsed three times, and residual biofilm viability was determined by CLSM, plate counts and prolonged culture up to 16 days. Isolates before and after exposure underwent minimum inhibitory concentration (MIC) and minimum eradication concentration (MEC) testing, and one pair underwent whole-genome sequencing.

Findings: Hypochlorite exposure reduced plate counts by a factor of 7 log10, and reduced biofilm biomass by a factor of 100; however, staining of residual biofilm showed that live S. aureus cells remained. On prolonged incubation, S. aureus regrew and formed biofilms. Post-exposure S. aureus isolates had MICs and MECs that were not significantly different from the parent strains. Whole-genome sequencing of one pre- and post-exposure pair found that they were virtually identical.

Conclusions: Hypochlorite exposure led to a 7-log kill but the organisms regrew. No resistance mutations occurred, implying that hypochlorite resistance is an intrinsic property of S. aureus biofilms. The clinical significance of this warrants further study.

Read the abstract here