Predictors of skin and soft tissue infections in HIV-infected outpatients in the community-associated methicillin-resistant Staphylococcus aureus era

Toxin expression during Staphylococcus aureus infection imprints host immunity to inhibit vaccine efficacy

Staphylococcus aureus infections are a major public health issue, and a vaccine is urgently needed. Despite a considerable promise in preclinical models, all vaccines tested thus far have failed to protect humans against S. aureus. Unlike laboratory mice, humans are exposed to S. aureus throughout life. In the current study, we hypothesized that prior exposure to S. aureus "imprints" the immune response to inhibit vaccine-mediated protection. We established a mouse model in which S. aureus skin and soft tissue infection (SSTI) is followed by vaccination and secondary SSTI. Unlike naïve mice, S. aureus-sensitized mice were incompletely protected against secondary SSTI by vaccination with the inactivated α-hemolysin (Hla) mutant Hla_H35L. Inhibition of protection was specific for the Hla_H35L vaccine and required hla expression during primary SSTI. Surprisingly, inhibition occurred at the level of vaccine-elicited effector T cells; hla expression during primary infection limited the expansion of T cells and dendritic cells and impaired vaccine-specific T cell responses. Importantly, the T cell-stimulating adjuvant CAF01 rescued inhibition and restored vaccine-mediated protection. Together, these findings identify a potential mechanism for the failure of translation of promising S. aureus vaccines from mouse models to clinical practice and suggest a path forward to prevent these devastating infections.

Skin and Soft Tissue Infection in People Living With Human Immunodeficiency Virus in a Large, Urban, Public Healthcare System in Houston, Texas, 2009-2014

BACKGROUND

Skin and soft tissue infections (SSTIs) disproportionately impact patients with human immunodeficiency virus (HIV). Recent declines in the incidence of SSTIs have been noted in the non-HIV population. We sought to study the epidemiology and microbiology of SSTIs in a population of 8597 patients followed for HIV primary care in a large, urban county system from January 2009 to December 2014.

METHODS

SSTIs were identified from the electronic medical record by use of International Classification of Diseases-9 billing codes. Charts were reviewed to confirm each patient's diagnosis of acute SSTI and abstract culture and susceptibility data. We calculated the yearly SSTI incidences using Poisson regression with clustering by patient.

RESULTS

There were 2202 SSTIs identified. Of 503 (22.8%) cultured SSTIs, 332 (66.0%) recovered Staphylococcus aureus as a pathogen, of which 287/332 (86.4%) featured S. aureus as the sole isolated organism. Among the S. aureus isolates that exhibited antibiotic susceptibilities, 231/331 (69.8%) were methicillin resistant, and the proportion did not change by year. The observed incidence of SSTI was 78.0 per 1000 person-years (95% confidence interval 72.9-83.4) and declined from 96.0 infections per 1000 person-years in 2009 to 56.5 infections per 1000 person-years in 2014 (P < .001). Other significant predictors of SSTI incidences in both univariate as well as multivariate analyses included a low CD4 count, high viral load, and not being a Spanish-speaking Hispanic.

CONCLUSIONS

SSTIs remain a significant problem in the outpatients living with HIV, although rates of SSTIs appear to have declined by approximately 40% between 2009 and 2014.

Hospitalization Rates and Causes Among Persons With HIV in the United States and Canada, 2005-2015

BACKGROUND

To assess the possible impact of antiretroviral therapy improvements, aging, and comorbidities, we examined trends in all-cause and cause-specific hospitalization rates among persons with HIV (PWH) from 2005 to 2015.

METHODS

In 6 clinical cohorts, we followed PWH in care (≥1 outpatient CD4 count or HIV load [VL] every 12 months) and categorized ICD codes of primary discharge diagnoses using modified Clinical Classifications Software. Poisson regression estimated hospitalization rate ratios for calendar time trends, adjusted for demographics, HIV risk factor, and annually updated age, CD4, and VL.

RESULTS

Among 28 057 patients (125 724 person-years), from 2005 to 2015, the median CD4 increased from 389 to 580 cells/µL and virologic suppression from 55% to 85% of patients. Unadjusted all-cause hospitalization rates decreased from 22.3 per 100 person-years in 2005 (95% confidence interval [CI], 20.6-24.1) to 13.0 in 2015 (95% CI, 12.2-14.0). Unadjusted rates decreased for almost all diagnostic categories. Adjusted rates decreased for all-cause, cardiovascular, and AIDS-defining conditions, increased for non-AIDS-defining infection, and were stable for most other categories.

CONCLUSIONS

Among PWH with increasing CD4 counts and viral suppression, unadjusted hospitalization rates decreased for all-cause and most cause-specific hospitalizations, despite the potential effects of aging, comorbidities, and cumulative exposure to HIV and antiretrovirals.

Decreasing Incidence of Skin and Soft-tissue Infections in 86 US Emergency Departments, 2009-2014

Background

The incidence of skin and soft-tissue infections (SSTIs), for which human immunodeficiency virus (HIV) is a significant risk factor, in United States emergency departments (EDs) increased dramatically after 2000 with the emergence of community-associated methicillin-resistant Staphylococcus aureus. Few studies have examined SSTI incidence among HIV-infected and non-HIV-infected patients in the United States after 2010.

Methods

Data were obtained for patient encounters at all academic medical center EDs affiliated with the Vizient clinical data warehouse assigned an SSTI-associated code based on the International Classification of Diseases, Ninth Revision, between 1 January 2009 and 31 December 2014. The rate was calculated per 1000 ED encounters by year and stratified by SSTI, HIV infection, or both, and by age group, race, payer type, and region of care. Poisson regression was used to assess temporal change over the study period.

Results

In 2009-2014, a total of 47317 HIV-associated and 820440 SSTI-associated encounters were recorded among 25239781 ED patient encounters. The rate of SSTIs decreased by 8% among all patients and by 14.6%, among those with HIV infection. The SSTI incidence overall decreased from 32.0 to 29.7 per 1000 ED encounters between 2009 and 2014. HIV-infected patients had a significantly higher rate of SSTIs than HIV-uninfected patients (adjusted rate ratio, 1.91; 95% confidence interval, 1.84-1.99).

Conclusions

The decline in SSTI incidence in US EDs between 2009 and 2014 is a remarkable epidemiologic shift from the increase in SSTIs after 2000, and further research is necessary to assess reasons for this decrease.

Does active hepatitis C virus infection increase the risk for infection due to Staphylococcus aureus?

Infections with Staphylococcus aureus may be more frequent in subjects with active hepatitis C virus (HCV) infection. In this retrospective dual-cohort study, we sought to determine whether persons with active HCV infection (positive HCV antibody, detectable blood HCV RNA) were at greater risk of S. aureus infection than those with spontaneously resolved HCV infection (positive HCV antibody, negative blood HCV RNA). Based on prestudy power calculation, we included 231 subjects with active HCV and 116 subjects with resolved HCV infection. The two groups were well matched at baseline, except that subjects with active HCV had a higher mean Charlson's comorbidity index (2.2 vs. 1.3; p < 0.0001). Cohorts were followed for a mean of 3.67 years. Thirty-one of the 231 (13%) subjects with active HCV infection developed ≥1 S. aureus infection(s) as compared to 4/116 (3.4%) subjects with resolved HCV (p = 0.004), with a trend towards more recurrent S. aureus infections in subjects with active HCV infection. The S. aureus infections were mostly serious, necessitating hospitalization and intravenous antibiotics. In the logistic regression, factors that independently predicted S. aureus infection were active HCV and Charlson's comorbidity index. Our regression models confirmed that the enhanced susceptibility to S. aureus infections was related to active HCV infection and not attributable solely to the increased number of comorbidities [adjusted odds ratio (OR) = 3.3, 95% confidence interval (CI) 1.1-9.8; p = 0.03]. This study shows that subjects with active HCV infection have a significantly higher incidence of serious S. aureus infections than those with spontaneously resolved HCV, even after adjustment for comorbidities.

The complex relationship between CD4 count, HIV viral load, trimethoprim-sulfamethoxazole prophylaxis, and skin-and-soft-tissue infection risk in patients with HIV: insights from a causal diagram and simulation study

Skin and soft tissue infection (SSTIs) due to Staphylococcus aureus, particularly community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), are common in human immunodeficiency virus (HIV)-infected populations in the United States. Studies have differed as to the importance of epidemiological and immunological factors in this relationship, and have employed conflicting strategies for variable selection in multivariate analyses. Developments in causal inference methods in epidemiology have emerged in the last decade to clarify relationships between variables and identify appropriate variables to include in and exclude from multivariate analysis. In this paper, we develop a causal diagram to clarify the pathways linking CA-MRSA and HIV. We focus on the role played by trimethoprim-sulfamethoxazole (TMP-SMX) prophylaxis, prescribed to many severely immunocompromised HIV patients and potentially protective against SSTIs, which both mediates and moderates the relationship between immunological parameters and SSTI risk. We demonstrate, using simulated data, that statistical models may yield biased results if they do not account for how HIV viral load may also be a marker of adherence to TMP-SMX prophylaxis. We conclude with a proposed causal model that includes both the epidemiological as well as immunological factors that may explain the increased risk of initial and recurrent SSTI risk in HIV-infected populations.

Importance of B Lymphocytes and the IgG-Binding Protein Sbi in Staphylococcus aureus Skin Infection

Recurrent Staphylococcus aureus infections are common, suggesting that immunity elicited by these infections is not protective. We previously reported that S. aureus skin infection (SSTI) elicited antibody-mediated immunity against secondary SSTI in BALB/c mice. In this study, we investigated the role of humoral immunity and the IgG-binding proteins Sbi and SpA in S. aureus SSTI. We found that B lymphocyte-deficient μMT mice were highly susceptible to infection, compared with congenic BALB/c mice. Importantly, transfer of immune serum protected μMT mice, demonstrating an appropriate response to protective antibody. We found that deletion of sbi, but not spa, impaired virulence, as assessed by skin lesion severity, and that Sbi-mediated virulence required B lymphocytes/antibody. Furthermore, neither Sbi nor SpA impaired the elicited antibody response or protection against secondary SSTI. Taken together, these findings highlight a B lymphocyte/antibody-dependent role of Sbi in the pathogenesis of S. aureus SSTI, and demonstrate that neither Sbi nor SpA interfered with elicited antibody-mediated immunity.

Host factors that contribute to recurrent staphylococcal skin infection

PURPOSE OF REVIEW

Staphylococcus aureus is the most common cause of skin and soft tissue infections (SSTI) in the United States and elsewhere. Recurrent infections occur frequently in patients with S. aureus SSTI, underscoring the need to better understand the nature of protective immunity against these infections. Here, we review recent findings concerning the host factors that predispose to S. aureus SSTI.

RECENT FINDINGS

Recurrent infections occur in nearly half of all patients with S. aureus SSTI. Epidemiologic and environmental factors, such as exposure to healthcare, age, and household contacts with S. aureus SSTI, and contaminated household fomites are associated with recurrence. The majority of the population has evidence of antistaphylococcal antibodies, but whether these are protective remains enigmatic. In contrast, recent clinical and experimental findings clearly highlight the critical roles of innate and T cell-mediated immunity in defense against these infections. S. aureus interferes with innate and adaptive immunity by a number of recently elucidated mechanisms.

SUMMARY

Recurrent S. aureus SSTIs are common, suggesting incomplete or absent protective immunity among these patients. Our understanding of protective immunity against recurrent infections is incomplete, and further basic and translational investigation is urgently needed to design strategies to prevent and treat these infections.

Recurrent skin and soft tissue infections in HIV-infected patients during a 5-year period: incidence and risk factors in a retrospective cohort study

Background

Skin and soft tissue infections (SSTIs) are common in the era of community-associated methicillin resistant Staphylococcus aureus among HIV-infected patients. Recurrent infections are frequent. Risk factors for recurrence after an initial SSTI have not been well-studied.

Methods

Retrospective cohort study, single center, 2005–2009. Paper and electronic medical records were reviewed by one of several physicians. Subjects with initial SSTI were followed until the time of SSTI recurrence. Standard descriptive statistics were calculated to describe the characteristics of subjects who did and did not develop a recurrent SSTI. Kaplan-Meier methods were used to estimate the risk of recurrent SSTI. A Cox regression model was developed to identify predictors of SSTI recurrence.

Results

133 SSTIs occurred in 87 individuals. 85 subjects were followed after their initial SSTI, of whom 30 (35.3 %) had a recurrent SSTI in 118.3 person-years of follow-up, for an incidence of second SSTI of 253.6 SSTIs/1000 person-years (95 % CI 166.8-385.7). The 1-year Kaplan-Meier estimated risk of a second SSTI was 29.2 % (95 % CI 20.3–41.0 %), while the 3-year risk was 47.0 % (95 % CI 34.4–61.6 %). Risk factors for recurrent SSTI in a multivariable Cox regression model were non-hepatitis liver disease (HR 3.44; 95 % CI 1.02–11.5; p = 0.05), the presence of an intravenous catheter (HR 6.50; 95 % CI 1.47–28.7; p = 0.01), and a history of intravenous drug use (IVDU) (HR 2.80; 95 % CI 1.02-7.65; p = 0.05); African-American race was associated with decreased risk of recurrent SSTI (HR 0.12; 95 % CI 0.04-0.41; p < 0.01). Some evidence was present for HIV viral load ≥ 1000 copies/mL as an independent risk factor for recurrent SSTI (HR 2.21; 95 % CI 0.99-4.94; p = 0.05). Hemodialysis, currently taking HAART, CD4+ count, trimethoprim-sulfamethoxazole or azithromycin use, initial SSTI type, diabetes mellitus, incision and drainage of the original SSTI, or self-report of being a man who has sex with men were not associated with recurrence.

Conclusion

Of HIV-infected patients with an SSTI, nearly 1/3 had a recurrent SSTI within 1 year. Risk factors for recurrent SSTI were non-hepatitis liver disease, intravenous catheter presence, a history of IVDU, and non-African-American race. Low CD4+ count was not a significant risk factor for recurrence.