Disparities in Mpox Vaccination Among Priority Populations During the 2022 Outbreak.

Background: The 2022 mpox outbreak disproportionately affected men who have sex with men and persons living with HIV (PLWH). A 2-dose mpox vaccine series was deployed in mid-2022. Structural racism and insurance status may have affected equitable vaccination. Methods: We defined 3 cohorts: PLWH with at least 1 clinic visit between 1 July 2021 and 1 July 2022 (n = 2066), HIV preexposure prophylaxis (PrEP) recipients as of 1 January 2022 (n = 262), and all mpox-vaccinated patients in our health system between 1 July 2022 and 30 November 2022 (n = 807). We identified patients with prior diagnosed sexually transmitted infections (STIs) as having a positive test result for gonorrhea, chlamydia, or syphilis between 1 July 2021-1 July 2022. The primary outcome was receipt of at least 1 dose of mpox vaccine. Results: We identified 224 (10.8%) PLWH and 50 (19.0%) PrEP patients who received at least 1 dose of mpox vaccine. Among PLWH, White race (odds ratio [OR], 1.55; 95% CI, 1.11-2.16), private insurance (OR, 1.83; 95% CI, 1.01-3.34), prior STI (OR, 3.04; 95% CI, 2.16-4.27), prior COVID-19 vaccination (OR, 3.17; 95% CI, 1.93-5.20), and prior influenza vaccination (OR, 1.42; 95% CI, 1.30-1.96) independently predicted mpox vaccination. Within the PrEP cohort, prior COVID-19 vaccination and seasonal influenza vaccination predicted mpox vaccination. Uninsured patients were vaccinated later in the outbreak than patients with private insurance (median time to vaccination, 41 days in the privately insured group vs 83 days in the uninsured group; P < .0001). Conclusions: Race, insurance status, prior STI, and previous receipt of other vaccines influenced uptake of mpox vaccine. Addressing health disparities and vaccine acceptance will be essential in improving future outbreak response.

Concurrent Sexually Transmitted Infection Testing Among Patients Tested for Mpox at a Tertiary Healthcare System.

Coinfection with sexually transmitted infections (STIs) and mpox is common. We evaluated concurrent STI testing among Duke Health patients tested for mpox. We found that most patients tested for mpox were not comprehensively tested for STIs, despite concurrent STIs being diagnosed in 15% of patients when testing was performed.

Electronic health record-based readmission risk model performance for patients undergoing outpatient parenteral antibiotic therapy (OPAT).

BACKGROUND: Outpatient Parenteral Antibiotic Therapy (OPAT) provides coordinated services to deliver parenteral antibiotics outside of the acute care setting. However, the reduction in monitoring and supervision may impact the risks of readmission to the hospital. While identifying those at greatest risk of hospital readmission through use of computer decision support systems could aid in its prevention, validation of such tools in this patient population is lacking. OBJECTIVE: The primary aim of this study is to determine the ability of the electronic health record-embedded EPIC Unplanned Readmission Model 1 to predict all-cause 30-day hospital unplanned readmissions in discharged patients receiving OPAT through the Duke University Heath System (DUHS) OPAT program. We then explored the impact of OPAT-specific variables on model performance. METHODS: This retrospective cohort study included patients ≥ 18 years of age discharged to home or skilled nursing facility between July 1, 2019 -February 1, 2020 with OPAT care initiated inpatient and coordinated by the DUHS OPAT program and with at least one Epic readmission score during the index hospitalization. Those with a planned duration of OPAT < 7 days, receiving OPAT administered in a long-term acute care facility (LTAC), or ongoing renal replacement therapy were excluded. The relationship between the primary outcome (unplanned readmission during 30-day post-index discharge) and Epic readmission scores during the index admission (discharge and maximum) was examined using multivariable logistic regression models adjusted for additional predictors. The performance of the models was assessed with the scaled Brier score for overall model performance, the area under the receiver operating characteristics curve (C-index) for discrimination ability, calibration plot for calibration, and Hosmer-Lemeshow goodness-of-fit test for model fit. RESULTS: The models incorporating maximum or discharge Epic readmission scores showed poor discrimination ability (C-index 0.51, 95% CI 0.45 to 0.58 for both models) in predicting 30-day unplanned readmission in the Duke OPAT cohort. Incorporating additional OPAT-specific variables did not improve the discrimination ability (C-index 0.55, 95% CI 0.49 to 0.62 for the max score; 0.56, 95% CI 0.49 to 0.62 for the discharge score). Although models for predicting 30-day unplanned OPAT-related readmission performed slightly better, discrimination ability was still poor (C-index 0.54, 95% CI 0.45 to 0.62 for both models). CONCLUSION: EPIC Unplanned Readmission Model 1 scores were not useful in predicting either all-cause or OPAT-related 30-day unplanned readmission in the DUHS OPAT cohort. Further research is required to assess other predictors that can distinguish patients with higher risks of 30-day unplanned readmission in the DUHS OPAT patients.

Utility of a risk assessment model in predicting 30†day unplanned hospital readmission in adult patients receiving outpatient parenteral antimicrobial therapy.

Objectives: Outpatient parenteral antimicrobial therapy (OPAT) is associated with high hospital readmission rates. A 30 day unplanned readmission risk prediction model for OPAT patients has been developed in the UK. Given significant differences in patient mix and methods of OPAT delivery, we explored the model for its utility in Duke University Health System (DUHS) patients receiving OPAT. Methods: We analysed OPAT episodes of adult patients from two hospitals between 1 July 2019 and 1 February 2020. The discriminative ability of the model to predict 30 day unplanned all-cause and OPAT-related admission was examined. An updated model was created by logistic regression with the UK risk factors and additional risk factors, OPAT delivery in a skilled nursing facility, vancomycin use and IV drug abuse. Results: Compared with patients of the UK cohort, our study patients were of higher acuity, treated for more invasive infections, and received OPAT through different modes. The 30 day unplanned readmission rate in our cohort was 20% (94/470), with 59.5% (56/94) of those being OPAT-related. The original model was unable to discriminate for all-cause readmission with a C-statistic of 0.52 (95% CI 0.46-0.59) and for OPAT-related readmission with a C-statistic of 0.55 (95% CI 0.47-0.64). The updated model with additional risk factors did not have improved performance, with a C-statistic of 0.55 (95% CI 0.49-0.62). Conclusions: The UK 30 day unplanned hospital readmission model performed poorly in predicting readmission for the OPAT population at a US academic medical centre.

Estimated Methicillin-Resistant Staphylococcus aureus Decolonization in Intensive Care Units Associated With Single-Application Chlorhexidine Gluconate or Mupirocin.

Importance: Chlorhexidine gluconate (CHG) and mupirocin are widely used to decolonize patients with methicillin-resistant Staphylococcus aureus (MRSA) and reduce risks associated with infection in hospitalized populations. Quantifying the association of an application of CHG alone or in combination with mupirocin with risk of MRSA infection is important for studies evaluating alternative decolonization strategies or schedules and for identifying whether there is room for improved decolonizing agents. Objective: To estimate the proportion of patients with MRSA decolonized per application of CHG and mupirocin from existing population-level studies. Design, Setting, and Participants: A stochastic mathematical model of an 18-bed intensive care unit (ICU) in an academic medical center operating over 1 year was used to estimate parameters for the proportion of simulated patients with MRSA decolonized per application of CHG and mupirocin. The model was conducted using approximate bayesian computation with data from an existing meta-analysis of studies conducted from February 2005 through January 2015. Data were analyzed from January 2018 through November 2019. Exposure: A universal decolonization protocol for colonized patients in the ICU using CHG or CHG and mupirocin in combination was simulated. Main Outcomes and Measures: The proportion of patients with MRSA decolonized per application of CHG and mupirocin was estimated. Results: The estimated proportion of patients with MRSA decolonized per application of CHG was 0.15 (95% credible interval, 0.01-0.42), and the estimated proportion per application of mupirocin in conjunction with CHG was 0.15 (95% credible interval, 0.01-0.54). A lag in colonization detection was associated with decreases in the CHG estimate (0.11; 95% credible interval, 0.01-0.30) and mupirocin estimate (0.10; 95% credible interval, 0.00-0.34), which were sensitive to the value of the modeled contact rate between nurses and patients. A 1% increase in the value of this parameter was associated with a 0.73% increase in the estimated combined outcomes associated with CHG and mupirocin (95% CI: 0.71, 0.75). Gaps longer than 24 hours in the administration of decolonizing agents were associated with a decrease of within-ICU MRSA transmission. Compared with a mean (SD) of 1.23 (0.27) acquisitions per 1000 patient-days in scenarios with no decolonizing bathing, a bathing protocol administering CHG and mupirocin every 120 hours was associated with a mean (SD) acquisition rate of 1.03 (0.24) acquisitions per 1000 patient days, a 16.3% decrease (95% CI, 14.7%-18.0%; P > .001). Conclusions and Relevance: These findings suggest that there may be room for significant improvement in anti-MRSA disinfectants, including the compounds themselves and their delivery mechanisms. Despite the decolonization estimates found in this study, these agents are associated with robust outcomes after delays in administration, which may help in alleviating concerns over patient comfort and toxic effects.

Geographic analysis of latent tuberculosis screening: A health system approach.

BACKGROUND: Novel approaches are required to better focus latent tuberculosis infection (LTBI) efforts in low-prevalence regions. Geographic information systems, used within large health systems, may provide one such approach. METHODS: A retrospective, cross-sectional design was used to integrate US Census and Duke Health System data between January 1, 2010 and October 31, 2017 and examine the relationships between LTBI screening and population tuberculosis risk (assessed using the surrogate measure of proportion of persons born in tuberculosis-endemic regions) by census tract. RESULTS: The median proportion of Duke patients screened per census tract was 0.01 (range 0-0.1, interquartile range 0.01-0.03). The proportion of Duke patients screened within a census tract significantly but weakly correlated with the population risk. Furthermore, patients residing in census tracts with higher population tuberculosis risk were more likely to be screened with TST than with an IGRA (p<0.001). CONCLUSION: The weak correlation between patient proportion screened for LTBI and our surrogate marker of population tuberculosis risk suggests that LTBI screening efforts should be better targeted. This type of geography-based analysis may serve as an easily obtainable benchmark for LTBI screening in health systems with low tuberculosis prevalence.

Molecular Diagnostics for Mycobacterium tuberculosis Infection.

Resistance to antimycobacterial drugs is a major barrier to effective treatment of Mycobacterium tuberculosis infection. Molecular diagnostic techniques based on the association between specific gene mutations and phenotypic resistance to certain drugs offer the opportunity to rapidly ascertain whether drug resistance is present and to alter treatment before further resistance develops. Current barriers to successful implementation of rapid diagnostics include imperfect knowledge regarding the full spectrum of mutations associated with resistance, limited utilization of molecular diagnostics where they are most needed, and the requirement for specialized laboratory facilities to perform molecular testing. Further understanding of genotypic-phenotypic correlates of resistance and streamlined implementation platforms will be necessary to optimize the public health impact of molecular resistance testing for M. tuberculosis.

Impact of radiology reports on timely tuberculosis diagnosis.

PURPOSE: As tuberculosis becomes less common in higher income countries, clinician familiarity with the disease is declining. Little is known about how chest radiograph interpretations affect tuberculosis care. We sought to determine how tuberculosis-related terminology in an initial chest radiograph reading impacted patient care. STUDY DESIGN: We examined a retrospective cohort of patients with pulmonary tuberculosis in North Carolina from 1 January 2011 to 31 December 2014. Tuberculosis-related terminology was categorised into four mutually exclusive categories. The primary outcomes of interest were the time from the chest radiograph to (1) obtaining the first sputum specimen for acid-fast smear and mycobacterial culture, and (2) initiation of antituberculous treatment. RESULTS: Of 550 available chest radiograph reports, 175 (31.8%) contained the word 'tuberculosis', 30 (5.5%) contained the word 'mycobacteria' or 'granulomatous', 43 (7.8%) contained the word 'cavity', and 301 (54.7%) had none of the above terms mentioned. Patients with the word 'tuberculosis' in the radiology report had a significantly shorter time to collection of the initial sputum specimen for acid-fast smear and mycobacterial culture (median 2 days) and to the start of antituberculous treatment (median 4 days) than patients with none of the keywords. Use of the term 'cavity' in the report was associated with a shorter time to initiation of antituberculous treatment (median 4 days) than if none of the keywords were used. CONCLUSION: Chest radiograph reports that contained keywords for pulmonary tuberculosis, such as 'tuberculosis' or 'cavity', were associated with less time to collection of sputum and antituberculous treatment.

Suboptimal HIV Testing Among Patients Admitted With Pneumonia: A Missed Opportunity.

Patients admitted with pneumonia are at higher risk for HIV and should be routinely screened. We examined a retrospective cohort of patients admitted to Duke University Health System with a primary diagnosis of pneumonia. During the study period, 6,951 persons were admitted with pneumonia. Of 6,646 patients without a known prior diagnosis of HIV, 1,010 (15%) had HIV testing during admission and 1,516 (23%) had a previously documented HIV test result. Forty-one (0.6%) patients had a positive HIV test during admission and 27 (0.4%) patients were diagnosed with HIV a median of 498 (IQR 112-982) days later, with median CD4 count of 64 (IQR 16-281) cells/mm3. HIV testing rates remain low in a population at high risk for HIV. At a minimum, we should be adhering to universal HIV screening recommendations, and certainly we should be screening those at higher risk. Opt-out HIV testing of pneumonia inpatients should be implemented.

Clinical Outcomes and Healthcare Utilization Related to Multidrug-Resistant Gram-Negative Infections in Community Hospitals.

OBJECTIVE To evaluate the impact of multidrug-resistant gram-negative rod (MDR-GNR) infections on mortality and healthcare resource utilization in community hospitals. DESIGN Two matched case-control analyses. SETTING Six community hospitals participating in the Duke Infection Control Outreach Network from January 1, 2010, through December 31, 2012. PARTICIPANTS Adult patients admitted to study hospitals during the study period. METHODS Patients with MDR-GNR bloodstream and urinary tract infections were compared with 2 groups: (1) patients with infections due to nonMDR-GNR and (2) control patients representative of the nonpsychiatric, non-obstetric hospitalized population. Four outcomes were assessed: mortality, direct cost of hospitalization, length of stay, and 30-day readmission rates. Multivariable regression models were created to estimate the effect of MDR status on each outcome measure. RESULTS No mortality difference was seen in either analysis. Patients with MDR-GNR infections had 2.03 higher odds of 30-day readmission compared with patients with nonMDR-GNR infections (95% CI, 1.04-3.97, P=.04). There was no difference in hospital direct costs between patients with MDR-GNR infections and patients with nonMDR-GNR infections. Hospitalizations for patients with MDR-GNR infections cost $5,320.03 more (95% CI, $2,366.02-$8,274.05, P<.001) and resulted in 3.40 extra hospital days (95% CI, 1.41-5.40, P<.001) than hospitalizations for control patients. CONCLUSIONS Our study provides novel data regarding the clinical and financial impact of MDR gram-negative bacterial infections in community hospitals. There was no difference in mortality between patients with MDR-GNR infections and patients with nonMDR-GNR infections or control patients. Infect Control Hosp Epidemiol 2016;1-8.

Epidemiology of Surgical Site Infection in a Community Hospital Network.

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.

A Multicenter Pragmatic Interrupted Time Series Analysis of Chlorhexidine Gluconate Bathing in Community Hospital Intensive Care Units.

OBJECTIVE To determine whether daily chlorhexidine gluconate (CHG) bathing of intensive care unit (ICU) patients leads to a decrease in hospital-acquired infections (HAIs), particularly infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE). DESIGN Interrupted time series analysis. SETTING The study included 33 community hospitals participating in the Duke Infection Control Outreach Network from January 2008 through December 2013. PARTICIPANTS All ICU patients at study hospitals during the study period. METHODS Of the 33 hospitals, 17 hospitals implemented CHG bathing during the study period, and 16 hospitals that did not perform CHG bathing served as controls. Primary pre-specified outcomes included ICU central-line-associated bloodstream infections (CLABSIs), primary bloodstream infections (BSI), ventilator-associated pneumonia (VAP), and catheter-associated urinary tract infections (CAUTIs). MRSA and VRE HAIs were also evaluated. RESULTS Chlorhexidine gluconate (CHG) bathing was associated with a significant downward trend in incidence rates of ICU CLABSI (incidence rate ratio [IRR], 0.96; 95% confidence interval [CI], 0.93-0.99), ICU primary BSI (IRR, 0.96; 95% CI, 0.94-0.99), VRE CLABSIs (IRR, 0.97; 95% CI, 0.97-0.98), and all combined VRE infections (IRR, 0.96; 95% CI, 0.93-1.00). No significant trend in MRSA infection incidence rates was identified prior to or following the implementation of CHG bathing. CONCLUSIONS In this multicenter, real-world analysis of the impact of CHG bathing, hospitals that implemented CHG bathing attained a decrease in ICU CLABSIs, ICU primary BSIs, and VRE CLABSIs. CHG bathing did not affect rates of specific or overall infections due to MRSA. Our findings support daily CHG bathing of ICU patients. Infect Control Hosp Epidemiol 2016;37:791-797.

An Automated Surveillance Strategy to Identify Infectious Complications After Cardiac Implantable Electronic Device Procedures.

Background. The optimum approach for infectious complication surveillance for cardiac implantable electronic device (CIED) procedures is unclear. We created an automated surveillance tool for infectious complications after CIED procedures. Methods. Adults having CIED procedures between January 1, 2005 and December 31, 2011 at Duke University Hospital were identified retrospectively using International Classification of Diseases, 9th revision (ICD-9) procedure codes. Potential infections were identified with combinations of ICD-9 diagnosis codes and microbiology data for 365 days postprocedure. All microbiology-identified and a subset of ICD-9 code-identified possible cases, as well as a subset of procedures without microbiology or ICD-9 codes, were reviewed. Test performance characteristics for specific queries were calculated. Results. Overall, 6097 patients had 7137 procedures. Of these, 1686 procedures with potential infectious complications were identified: 174 by both ICD-9 code and microbiology, 14 only by microbiology, and 1498 only by ICD-9 criteria. We reviewed 558 potential cases, including all 188 microbiology-identified cases, 250 randomly selected ICD-9 cases, and 120 with neither. Overall, 65 unique infections were identified, including 5 of 250 reviewed cases identified only by ICD-9 codes. Queries that included microbiology data and ICD-9 code 996.61 had good overall test performance, with sensitivities of approximately 90% and specificities of approximately 80%. Queries with ICD-9 codes alone had poor specificity. Extrapolation of reviewed infectious rates to nonreviewed cases yields an estimated rate of infection of 1.3%. Conclusions. Electronic queries with combinations of ICD-9 codes and microbiologic data can be created and have good test performance characteristics for identifying likely infectious complications of CIED procedures.

Short Operative Duration and Surgical Site Infection Risk in Hip and Knee Arthroplasty Procedures.

OBJECTIVE: To determine the association (1) between shorter operative duration and surgical site infection (SSI) and (2) between surgeon median operative duration and SSI risk among first-time hip and knee arthroplasties. DESIGN: Retrospective cohort study SETTING: A total of 43 community hospitals located in the southeastern United States. PATIENTS: Adults who developed SSIs according to National Healthcare Safety Network criteria within 365 days of first-time knee or hip arthroplasties performed between January 1, 2008 and December 31, 2012. METHODS: Log-binomial regression models estimated the association (1) between operative duration and SSI outcome and (2) between surgeon median operative duration and SSI outcome. Hip and knee arthroplasties were evaluated in separate models. Each model was adjusted for American Society of Anesthesiology score and patient age. RESULTS: A total of 25,531 hip arthroplasties and 42,187 knee arthroplasties were included in the study. The risk of SSI in knee arthroplasties with an operative duration shorter than the 25th percentile was 0.40 times the risk of SSI in knee arthroplasties with an operative duration between the 25th and 75th percentile (risk ratio [RR], 0.40; 95% confidence interval [CI], 0.38-0.56; P<.01). Short operative duration did not demonstrate significant association with SSI for hip arthroplasties (RR, 1.04; 95% CI, 0.79-1.37; P=.36). Knee arthroplasty surgeons with shorter median operative durations had a lower risk of SSI than surgeons with typical median operative durations (RR, 0.52; 95% CI, 0.43-0.64; P<.01). CONCLUSIONS: Short operative durations were not associated with a higher SSI risk for knee or hip arthroplasty procedures in our analysis.

Seasonal Variation of Common Surgical Site Infections: Does Season Matter?

OBJECTIVE: To evaluate seasonal variation in the rate of surgical site infections (SSI) following commonly performed surgical procedures. DESIGN: Retrospective cohort study. METHODS: We analyzed 6 years (January 1, 2007, through December 31, 2012) of data from the 15 most commonly performed procedures in 20 hospitals in the Duke Infection Control Outreach Network. We defined summer as July through September. First, we performed 3 separate Poisson regression analyses (unadjusted, multivariable, and polynomial) to estimate prevalence rates and prevalence rate ratios of SSI following procedures performed in summer versus nonsummer months. Then, we stratified our results to obtain estimates based on procedure type and organism type. Finally, we performed a sensitivity analysis to test the robustness of our findings. RESULTS: We identified 4,543 SSI following 441,428 surgical procedures (overall prevalence rate, 1.03/100 procedures). The rate of SSI was significantly higher during the summer compared with the remainder of the year (1.11/100 procedures vs 1.00/100 procedures; prevalence rate ratio, 1.11 [95% CI, 1.04-1.19]; P=.002). Stratum-specific SSI calculations revealed higher SSI rates during the summer for both spinal (P=.03) and nonspinal (P=.004) procedures and revealed higher rates during the summer for SSI due to either gram-positive cocci (P=.006) or gram-negative bacilli (P=.004). Multivariable regression analysis and sensitivity analyses confirmed our findings. CONCLUSIONS: The rate of SSI following commonly performed surgical procedures was higher during the summer compared with the remainder of the year. Summer SSI rates remained elevated after stratification by organism and spinal versus nonspinal surgery, and rates did not change after controlling for other known SSI risk factors.

Postoperative infection in spine surgery: does the month matter?

OBJECT: The relationship between time of year and surgical site infection (SSI) following neurosurgical procedures is poorly understood. Authors of previous reports have demonstrated that rates of SSI following neurosurgical procedures performed during the summer months were higher compared with rates during other seasons. It is unclear, however, if this difference was related to climatological changes or inexperienced medical trainees (the July effect). The aim of this study was to evaluate for seasonal variation of SSI following spine surgery in a network of nonteaching community hospitals. METHODS: The authors analyzed 6 years of prospectively collected surveillance data (January 1, 2007, to December 31, 2012) from all laminectomies and spinal fusions from 20 hospitals in the Duke Infection Control Outreach Network of community hospitals. Surgical site infections were defined using National Healthcare Safety Network criteria and identified using standardized methods across study hospitals. Regression models were then constructed using Poisson distribution to evaluate for seasonal trends by month. Each analysis was first performed for all SSIs and then for SSIs caused by specific organisms or classes of organisms. Categorical analysis was performed using two separate definitions of summer: June through September (definition 1), and July through September (definition 2). The prevalence rate of SSIs during the summer was compared with the prevalence rate during the remainder of the year by calculating prevalence rate ratios and 95% confidence intervals. RESULTS: The authors identified 642 SSIs following 57,559 neurosurgical procedures (overall prevalence rate = 1.11/100 procedures); 215 occurred following 24,466 laminectomies (prevalence rate = 0.88/100 procedures), and 427 following 33,093 spinal fusions (prevalence rate = 1.29/100 procedures). Common causes of SSI were Staphylococcus aureus (n = 380; 59%), coagulase-negative staphylococci (n = 90; 14%), and Escherichia coli (n = 41; 6.4%). Poisson regression models demonstrated increases in the rates of SSI during each of the summer months for all SSIs and SSIs due to gram-positive cocci, S. aureus, and methicillin-sensitive S. aureus. Categorical analysis confirmed that the rate of SSI during the 4-month summer period was higher than the rate during the remainder of the year, regardless of which definition for summer was used (definition 1, p = 0.008; definition 2, p = 0.003). Similarly, the rates of SSI due to grampositive cocci and S. aureus were higher during the summer months than the remainder of the year regardless of which definition of summer was used. However, the rate of SSI due to gram-negative bacilli was not. CONCLUSIONS: The rate of SSI following fusion or spinal laminectomy/laminoplasty was higher during the summer in this network of community hospitals. The increase appears to be related to increases in SSIs caused by gram-positive cocci and, more specifically, S. aureus. Given the nonteaching nature of these hospitals, the findings demonstrate that increases in the rate of SSI during the summer are more likely related to ecological and/or environmental factors than the July effect.