Incidence of and Risk Factors for Clinically Significant Methicillin-Resistant Staphylococcus aureus Infection in a Cohort of HIV-Infected Adults

Major but differential decline in the incidence of Staphylococcus aureus bacteraemia in HIV-infected individuals from 1995 to 2007: a nationwide cohort study*

OBJECTIVES

Incidence rates (IRs) of Staphylococcus aureus bacteraemia (SAB) are known to be higher in HIV-infected individuals than in the general population, but have not been assessed in the era of highly active antiretroviral therapy.

METHODS

From 1 January 1995 to 31 December 2007, all Danish HIV-infected individuals (n=4871) and population controls (n=92 116) matched on age and sex were enrolled in a cohort and all cases of SAB were registered. IRs and risk factors were estimated using time-updated Poisson regression analysis.

RESULTS

We identified 329 cases of SAB in 284 individuals, of whom 132 individuals were infected with HIV and 152 were not [crude IR ratio (IRR) 24.2; 95% confidence interval (CI) 19.5-30.0, for HIV-infected vs. non-HIV-infected individuals]. Over time, IR declined for HIV-infected individuals (IRR 0.40). Injecting drug users (IDUs) had the highest incidence and the smallest decline in IR, while men who have sex with men (MSM) had the largest decline over time. Among HIV-infected individuals, a latest CD4 count <100 cells/μL was the strongest independent predictor of SAB (IRR 10.2). Additionally, HIV transmission group was associated with risk of SAB. MSM were more likely to have hospital-acquired SAB, a low CD4 cell count and AIDS at the time of HIV acquisition compared with IDUs.

CONCLUSIONS

We found that the incidence of SAB among HIV-infected individuals declined during the study period, but remained higher than that among HIV-uninfected individuals. There was an unevenly distributed burden of SAB among HIV transmission groups (IDU>MSM). Low CD4 cell count and IDU were strong predictors of SAB among HIV-infected individuals.

Community-associated methicillin-resistant Staphylococcus aureus infections in men who have sex with men: A case series

BACKGROUND

The purpose of the present study was to describe the clinical characteristics and management of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections among a cohort of men who have sex with men.

PATIENTS AND METHODS

A retrospective chart review was conducted of patients with culture-proven MRSA at Maple Leaf Medical Clinic (Toronto, Ontario) between November 2004 and December 2005. Cases were identified by individual physicians and by queries in the clinical management system. A standard data collection form was used to record patient demographics, potential risk factors for MRSA and course of illness. When available, antimicrobial sensitivities were recorded. DNA fingerprinting using pulsed-field gel electrophoresis, and genetic analysis for SCCmec typing and detection of the Panton-Valentine leukocidin cytotoxin were performed on six available isolates.

RESULTS

Seventeen patients with MRSA infection were identified, 12 (71%) of whom were HIV-positive. The most common clinical presentation was abscess (35%), followed by furuncle (17%), folliculitis (17%), cellulitis (17%) and sinusitis (12%). The majority of MRSA isolates were resistant to ciprofloxacin (92%) and levofloxacin (77%). All isolates were susceptible to trimethoprim-sulfamethoxazole, rifampin, linezolid, gentamicin and clindamycin, while the majority were susceptible to tetracycline (80%). All six isolates tested were SCCmec type IVa-positive and Panton-Valentine leukocidin-positive, and had fingerprint patterns consistent with the CMRSA-10 (USA300) clone.

CONCLUSION

The present study describes the clinical presentation and management of CA-MRSA infections occurring in Toronto among men who have sex with men. The infections appear to have been caused by CMRSA-10, which has caused the majority of CA-MRSA outbreaks elsewhere.

The rise and fall of methicillin-resistant Staphylococcus aureus infections in HIV patients

We evaluated the annual and weighted incidence of methicillin-resistant Staphylococcus aureus infections by specific risk factors in a prospective cohort of HIV patients. We found 228 infections in 167 patients from 2002 to 2009. Higher rates were seen in men who have sex with men and intravenous drug users, patients with lower CD4 cell counts, patients not on antiretrovirals and younger patients. The annual incidence peaked in 2007 and has decreased since.

Incidence of and risk factors for bacteraemia in HIV-infected adults in the era of highly active antiretroviral therapy

BACKGROUND

HIV-infected patients have an increased risk for bacteraemia compared with HIV-negative patients. Few data exist on the incidence of and risk factors for bacteraemia across time in the current era of highly active antiretroviral therapy (HAART).

METHODS

We assessed the incidence of bacteraemia among patients followed between 2000 and 2008 at 10 HIV Research Network sites. This large multisite, multistate clinical cohort study collected demographic, clinical and therapeutic data longitudinally. International Statistical Classification of Diseases and Related Health Problems (ICD)-9 codes were examined to identify all cases of in-patient bacteraemia. Logistic regression analysis was used to assess risk factors for bacteraemia and trends over time in the odds of bacteraemia.

RESULTS

A total of 39 318 patients were followed for 146 289 person-years (PY). During the study period, there were 2025 episodes of bacteraemia (incidence 13.8 events/1000 PY). The most common bacteraemia diagnosis was 'bacteraemia, not otherwise specified (NOS)' (51%) followed by Staphylococcus aureus (16%) and Streptococcus species (6.5%). In multivariate analysis, the likelihood of bacteraemia was found to have increased in 2005-2008, compared with 2000. Other factors associated with higher odds of bacteraemia included a history of injection drug use (IDU), age ≥ 50 years, Black race and greater immunosuppression.

CONCLUSIONS

The likelihood of bacteraemia has risen slightly in recent years. Patients who are Black or have a history of IDU are at higher risk. Further research is needed to identify reasons for this increase and to evaluate programmes designed to reduce the bacteraemia risk.

Recurrent community-acquired methicillin-resistant Staphylococcus aureus infections in an HIV-infected person

HIV-infected persons are at heightened risk for recurrent community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections, but there are limited data regarding the molecular characterization of these events. We describe an HIV-infected patient with 24 soft tissue infections and multiple colonization events. Molecular genotyping from 33 nonduplicate isolates showed all strains were USA300, Panton-Valentine leukocidin (PVL) and arginine catabolic mobile element (ACME) positive, and genetically related.

Methicillin-resistant Staphylococcus aureus colonization in HIV-infected outpatients is common and detection is enhanced by groin culture

SUMMARYAlthough high rates of clinical infection with methicillin-resistant Staphylococcus aureus (MRSA) have been reported in HIV-infected adults, data on MRSA colonization are limited. We enrolled HIV-infected adults receiving care at the Atlanta VA Medical Center. Swabs from each participant's nares and groin were cultured with broth enrichment for S. aureus. Of 600 HIV-infected adults, 79 (13%) were colonized with MRSA and 180 (30%) with methicillin-susceptible S. aureus. MRSA pulsed-field gel electrophoresis types USA300 (n=44, 54%) and USA500/Iberian (n=29, 35%) predominated. Inclusion of groin swabs increased MRSA detection by 24% and USA300 detection by 38%. In multivariate analysis, MRSA colonization compared to no MRSA colonization was associated with a history of MRSA clinical infection, rarely or never using condoms, and contact with prisons and jails. In summary, the prevalence of MRSA colonization was high in this study of HIV-infected adults and detection of USA300 was enhanced by groin culture.

Methicillin-resistant Staphylococcus aureus in HIV-infected patients

Concordant with the emergence of methicillin-resistant Staphylococcus aureus (MRSA) in the community setting, colonization and infections with this pathogen have become a prevalent problem among the human immunodeficiency virus (HIV)-positive population. A variety of different host- and, possibly, pathogen-related factors may play a role in explaining the increased prevalence and incidence observed. In this article, we review pathophysiology, epidemiology, clinical manifestations, and treatment of MRSA in the HIV-infected population.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

Community-associated meticillin-resistant Staphylococcus aureus

Meticillin-resistant Staphylococcus aureus (MRSA) is endemic in hospitals worldwide, and causes substantial morbidity and mortality. Health-care-associated MRSA infections arise in individuals with predisposing risk factors, such as surgery or presence of an indwelling medical device. By contrast, many community-associated MRSA (CA-MRSA) infections arise in otherwise healthy individuals who do not have such risk factors. Additionally, CA-MRSA infections are epidemic in some countries. These features suggest that CA-MRSA strains are more virulent and transmissible than are traditional hospital-associated MRSA strains. The restricted treatment options for CA-MRSA infections compound the effect of enhanced virulence and transmission. Although progress has been made towards understanding emergence of CA-MRSA, virulence, and treatment of infections, our knowledge remains incomplete. Here we review the most up-to-date knowledge and provide a perspective for the future prophylaxis or new treatments for CA-MRSA infections.

IL-17 is essential for host defense against cutaneous Staphylococcus aureus infection in mice

Staphylococcus aureus is the most common cause of skin and soft tissue infections, and rapidly emerging antibiotic-resistant strains are creating a serious public health concern. If immune-based therapies are to be an alternative to antibiotics, greater understanding is needed of the protective immune response against S. aureus infection in the skin. Although neutrophil recruitment is required for immunity against S. aureus, a role for T cells has been suggested. Here, we used a mouse model of S. aureus cutaneous infection to investigate the contribution of T cells to host defense. We found that mice deficient in gammadelta but not alphabeta T cells had substantially larger skin lesions with higher bacterial counts and impaired neutrophil recruitment compared with WT mice. This neutrophil recruitment was dependent upon epidermal Vgamma5+ gammadelta T cell production of IL-17, but not IL-21 and IL-22. Furthermore, IL-17 induction required IL-1, TLR2, and IL-23 and was critical for host defense, since IL-17R-deficient mice had a phenotype similar to that of gammadelta T cell-deficient mice. Importantly, gammadelta T cell-deficient mice inoculated with S. aureus and treated with a single dose of recombinant IL-17 had lesion sizes and bacterial counts resembling those of WT mice, demonstrating that IL-17 could restore the impaired immunity in these mice. Our study defines what we believe to be a novel role for IL-17-producing epidermal gammadelta T cells in innate immunity against S. aureus cutaneous infection.

Risks for methicillin-resistant Staphylococcus aureus colonization or infection among patients with HIV infection

BACKGROUND

Risks for methicillin-resistant Staphylococcus aureus (MRSA) among those with HIV infection have been found to vary, and the epidemiology of USA-300 community-acquired (CA) MRSA has not been adequately described.

METHODS

We conducted a retrospective review of HIV-infected out-patients from January 2002 to December 2007 and employed multivariate logistic regression (MLR) to identify risks for MRSA colonization or infection. Pulsed-field gel electrophoresis (PFGE) was used to identify USA-300 strains.

RESULTS

Seventy-two (8%) of 900 HIV-infected patients were colonized or infected with MRSA. MLR identified antibiotic exposure within the past year [odds ratio (OR) 3.4; 95% confidence interval (CI) 1.5-7.7] and nadir CD4 count <200 cells/microL (OR 2.5; 95% CI 1.2-5.3) as risks for MRSA colonization or infection. Receipt of antiretroviral therapy (ART) within the past year was associated with decreased risk (OR 0.16; 95% CI 0.07-0.4). Eighty-nine percent of available strains were USA-300. MLR identified skin or soft tissue infection (SSTI) as the only predictor for infection with USA-300 (OR 5.9; 95% CI 1.4-24.3).

CONCLUSION

Significant risks for MRSA among HIV-infected patients were CD4 count nadir <200 cells/microL and antibiotic exposure. Only the presence of an SSTI was associated with having USA-300, and thus the use of patient characteristics to predict those with USA-300 was limited. In addition, ART within the previous year significantly reduced the risk of MRSA colonization or infection.

Gender Differences in Emerging Infectious Diseases

This chapter focuses on gender differences in emerging infectious diseases. An urgent worldwide threat is posed by the introduction and spread of novel infectious diseases. The reasons for emerging infectious diseases are numerous and complex. Among the most significant explanations for these emerging diseases are changes in environment and ecology caused by natural phenomena such as droughts, hurricanes, and floods; and human-made phenomena such as agricultural development, urbanization, and denuding of forests. Worldwide conflict, including wars, ethnic cleansing, and genocide, have led to displacement of large populations into overcrowded settlements where safe water is not available and sanitation is poor. For example, unsanitary conditions led to a huge increase in the rat population in post-war Kosovo, resulting in a tularemia outbreak with 327 confirmed cases in 8 months. Regional conflict leads to breakdown in infection control, inadequate surveillance, impeded access to populations, and spread of infectious diseases through movement of refugees and aid workers. Increased precipitation, a result of climate change, leads to more agricultural run-off, allowing pathogens to enter drinking water systems. In developing countries where poverty and inadequate infrastructure are the norm, public health monitoring systems must be supported and improved so that new or more severe risks to health can be identified and curtailed. As new infectious diseases are recognized, critical issues arise regarding pregnant women and their unborn children. Physiologic changes during pregnancy and gestational age both alter decision-making regarding vaccinations and medications.

Short communication: methicillin-resistant Staphylococcus aureus infections in children and young adults infected with HIV

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) infections, in particular with Panton-Valentine leukocidin (PVL)-positive strains, has not been well characterized in children and young adults with HIV infection. It is not known if PVL-positive strains of MRSA cause an increased morbidity in this population compared to PVL-negative strains. The purpose of this study was to retrospectively analyze the epidemiology of PVL-positive and PVL-negative MRSA infections in children and young adults with HIV from 2000 to 2007. Molecular typing was performed by polymerase chain reaction (PCR) for detection of the PVL genes. Staphylococcus Cassette Chromosome (SCC) mec and spa typing were performed on all PVL-positive isolates. The number of HIV patients with MRSA infection increased significantly between 2000 and 2007 ( p=0.0015). Twenty seven (87%) of the 31 MRSA isolates were from skin and soft tissue infections (SSTI). Clindamycin resistance was observed in 19% of the MRSA isolates. PVL-positive isolates bearing the type IV SCC mec element comprised 16 of 31 (52%) MRSA isolates. All the PVL-positive isolates belonged to the USA300 pulsed-field type. There was no difference in the mean CD4 count and HIV viral load between patients with PVL-positive and PVL-negative MRSA infections. PVL-positive MRSA infections were associated with more SSTI ( p=0.043) but not with increased morbidity or a higher risk of complications compared to PVL-negative MRSA infections in children and young adults with HIV.

Trimethoprim-sulfamethoxazole for methicillin-resistant Staphylococcus aureus: a forgotten alternative?

Methicillin-resistant Staphylococcus aureus (MRSA) is a growing infectious concern, mainly in the context of its rapid adaptation to novel antibiotic options for its treatment and the growing morbidity, mortality, and healthcare costs associated with its emergence. the authors sought to investigate whether an older antibiotic, such as trimethoprim-sulfamethoxazole (SXT), may have a role in treating MRSA-related infections, according to the available literature on the subject. The authors reviewed literature data on: resistance of MRSA to SXT worldwide in recent years, efficacy of SXT for MRSA decolonization or prophylaxis from MRSA infections, and clinical therapeutic efficacy of SXT in treating mild or severe community-acquired or hospital-acquired MRSA infections. Resistance varies worldwide, in general being low in the industrialized world and higher in developing countries. SXT is one of the numerous understudied options for MRSA decolonization and is growingly recognized as potentially effective in preventing MRSA infections in certain settings. Limited data on its therapeutic efficacy are encouraging, at least for mild, community-acquired infections. SXT may represent a cost-effective alternative weapon against MRSA. Its utility against this increasingly threatening pathogen need clarification through further clinical trials.

Recurrent community-associated methicillin-resistant Staphylococcus aureus infections among HIV-infected persons: incidence and risk factors

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are well described among the general population, but little is known regarding the incidence of and predictors for recurrent CA-MRSA infections among HIV-infected persons. We retrospectively evaluated HIV-infected patients seen at the Naval Medical Center San Diego from January 1, 2000 to June 30, 2007 for wound culture-proven MRSA infections defined as community-associated based on Centers for Disease Control and Prevention (CDC) criteria. Data on skin/soft tissue infections (SSTIs) following an initial CA-MRSA infection were collected by review of medical records and culture results. Patients with or without recurrent infections were compared for predictors of recurrence using multivariate logistic regression models. Thirty-one (6.8%) of 458 patients with HIV had wound culture-proven CA-MRSA SSTIs for an incidence rate of 12.3 infections per 1000 person-years. Those who developed a MRSA infection had a mean age of 40 years, 97% were male, 58% were Caucasian, 23% were Hispanic, 16% were African American, and 3% were other; demographics were similar to the overall study population. Fourteen (41%) HIV patients with an initial MRSA infection had recurrent SSTIs; of these, seven (21%) had culture-confirmed recurrent CA-MRSA. The median time between infection recurrences was 4 months (range, 1-20 months). Suppressed HIV-1 RNA levels of less than 1000 copies per milliliter (odds ratio [OR] 0.14, p = 0.03) was associated with a lower rate of SSTI recurrence. In summary, HIV-infected persons have a high incidence of CA-MRSA skin/soft tissue infections and a high rate of recurrence. HIV control may be associated with a reduced risk of recurrent skin/soft tissue infections.

Community-Associated Methicillin-Resistant Staphylococcus aureus Skin and Soft-Tissue Infection in HIV-Infected Patients

Background. Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as the most common cause of skin and soft tissue infections (SSTIs). Methods. Retrospective chart review of 43 adult HIV-infected patients with CA-MRSA SSTI was conducted. Results. Antibiotic susceptibility was as follows: vancomycin (100%), rifampin (100%), gentamicin (97.7%), tetracycline (96.5%), trimethoprim-sulfamethoxazole (95.2%), clindamycin (89.5%), levofloxacin (66.7%), and erythromycin (6.9%). At SSTI presentation, 58.5% of patients had CD4 counts greater than 200 cells/uL, 82.9% had a viral load (VL) below 100 000 log copies/mL, 6 of whom had undetectable VL. All 43 patients received empiric antibiotic therapy. Additionally, 34 patients underwent incision and drainage (I&D). For the 37 patients with follow-up data available at 4 weeks, 30 of the infections were resolved/resolving and 7 had no improvement or worsened. Conclusion. A majority of our patients with CA-MRSA SSTI did not have immunological/virological markers consistent with severe HIV/AIDS disease at time of presentation.

Meningitis Due to Hematogenous Dissemination of Community-Associated Methicillin-Resistant Staphylococcus aureus (MRSA) in a Patient With AIDS

Meningitis due to methicillin-resistant Staphylococcus aureus is a rare clinical presentation but has been well documented in postneurosurgical patients. To our knowledge, no case of methicillin-resistant Staphylococcus aureus meningitis has been previously reported in a nonneurosurgical patient with AIDS. In this case report we describe a person with AIDS who had no history of a neurosurgical procedure, shunt devices, head trauma, or recent hospitalization that presented with methicillin-resistant Staphylococcus aureus meningitis. The infection was successfully treated. Methicillin-resistant Staphylococcus aureusshould be considered in the differential of meningitis in people with AIDS.

Prevalence of and risk factors for methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization in HIV-infected ambulatory patients

BACKGROUND

Estimates of the prevalence of colonization with methicillin-resistant Staphylococcus aureus (MRSA) vary in HIV-infected patients.

METHODS

HIV clinic patients were prospectively cultured. Bilateral nasal and axillary swabs were plated on BBL CHROMagar MRSA media. Molecular typing was done by pulse-field gel electrophoresis, and staphylococcal cassette chromosomemec typing was determined. A patient questionnaire was conducted to ascertain potential MRSA risk factors; medical records were reviewed.

RESULTS

Fifteen of 146 (10.3%) patients had MRSA nasal colonization; 1 also had axillary colonization. Twelve of 15 isolates were staphylococcal cassette chromosomemec type IV, and 8 of 14 were USA300 or USA400 genotype. MRSA colonization was associated with lower CD4 cell count, not receiving current or recent antibiotics, history of prior MRSA or methicillin-susceptible Staphylococcus aureus infection (P < 0.05 for all), and a trend toward history of hospitalization or emergency department visit in the past year (P = 0.064). Current use of trimethoprim-sulfamethoxazole was protective for colonization: 0 of 29 trimethoprim-sulfamethoxazole recipients were colonized versus 15 of 117 nonrecipients, P = 0.04. In a multivariate logistic regression model, prior infection with either methicillin-susceptible S. aureus (odds ratio = 32.4, 95% confidence interval 3.04 to 345.42) or MRSA (odds ratio = 9.71, 95% confidence interval 2.20 to 43.01), not receiving current or recent antibiotics (odds ratio = 0.026, 95% confidence interval 0.002 to 0.412), and lower CD4 count (odds ratio 0.996, 95% confidence interval 0.992 to 0.999) were associated with MRSA colonization.

DISCUSSION

The prevalence of MRSA nasal colonization was relatively high compared with prior studies; axillary colonization was rare. Prior staphylococcal infection (methicillin-susceptible S. aureus or MRSA), not receiving antibiotics, and lower CD4 count were associated with MRSA nasal colonization. Trimethoprim-sulfamethoxazole seemed to be protective of MRSA colonization.

The incidence of and risk factors for MRSA bacteraemia in an HIV-infected cohort in the HAART era

OBJECTIVES

To define the incidence and risk factors for methicillin resistant Staphylococcus aureus (MRSA) bacteraemia in an HIV-infected population.

METHODS

From January 1, 2000 to December 31, 2004, we conducted a retrospective cohort study. We identified all cases of Staphylococcus aureus bacteraemia (SAB), including MRSA, among patients enrolled in the Johns Hopkins Hospital out-patient HIV clinic. A conditional logistic regression model was used to identify risk factors for MRSA bacteraemia compared with methicillin-sensitive SAB and no bacteraemia in unmatched (1:1) and matched (1:4) nested case-control analyses, respectively.

RESULTS

Of 4607 patients followed for a total of 11 020 person-years (PY) of follow-up, 216 episodes of SAB occurred (incidence: 19.6 cases per 1000 PY), including 94 cases (43.5%) which were methicillin-resistant. The incidence of MRSA bacteraemia increased from 5.3 per 1000 PY in 2000-2001 to 11.9 per 1000 PY in 2003-2004 (P=0.001). Multivariate analysis demonstrated that independent predictors of MRSA bacteraemia (vs. no bacteraemia) were injection drug use (IDU), end-stage renal disease (ESRD) and CD4 count <200 cells/microL.

CONCLUSIONS

MRSA bacteraemia was an increasingly common diagnosis in our HIV-infected cohort, especially in patients with history of IDU, low CD4 cell count and ESRD.

Penile cellulitis due to community-acquired methicillin-resistant Staphylococcus aureus in an HIV-positive man

This is a study of aggressive penile cellulitis in an HIV-positive man due to community-acquired methicillin-resistant Staphylococcus aureus. Discussion focuses on the importance of recognizing this pathogen in the sexual health setting and possible causes of penile cellulitis.

Clinical practice: colonization, fomites, and virulence: rethinking the pathogenesis of community-associated methicillin-resistant Staphylococcus aureus infection

Community-associated methicillin-resistant Staphylococcus aureus (MRSA) infection is increasingly common worldwide and causes considerable morbidity and mortality. Of concern, community-associated MRSA infections are often recurrent and are highly transmissible to close contacts. The traditional tenet of pathogenesis is that MRSA colonization precedes infection. This has prompted persons involved in efforts to prevent community-associated MRSA infection to incorporate the use of intranasal topical antibiotics for nasal decolonization. However, data from outbreaks of community-associated MRSA infection suggest that skin-skin and skin-fomite contact represent important and common alternative routes of acquisition of the infecting strain. Furthermore, strain characteristics of the most successful community-associated MRSA strain, USA300, may contribute to a distinct pathogenesis. As we develop strategies to prevent community-associated MRSA infection, we must reconsider the pathogenesis of S. aureus. Reliance on models of health care-associated MRSA transmission for prevention of community-associated MRSA infection may result in the development of flawed strategies that attenuate our ability to prevent this serious and potentially deadly infection.

Community factors in the development of antibiotic resistance

The global impact of antibiotic resistance is potentially devastating, threatening to set back progress against certain infectious diseases to the pre-antibiotic era. Although most antibiotic-resistant bacteria originally emerged in hospitals, drug-resistant strains are becoming more common in the community. Factors that facilitate the development of resistance within the community can be categorized as behavioral or environmental/policy. Behavioral factors include inappropriate use of antibiotics and ineffective infection control and hygiene practices. Environmental/policy factors include the continued use of antibiotics in agriculture and the lack of new drug development. A multifaceted approach that includes behavioral strategies in the community and the political will to make difficult regulatory decisions will help to minimize the problem of antimicrobial resistance globally.

Trends in prescribing beta-lactam antibiotics for treatment of community-associated methicillin-resistant Staphylococcus aureus infections

Rates of prescribing of beta-lactam antibiotics as initial empirical therapy for patients with skin and soft tissue infections (SSTIs) caused by molecularly and epidemiologically characterized community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) isolates were assessed over a 3-year period. A prospectively developed database was used to calculate the prevalence of CA-MRSA SSTIs from 2004 to 2006. Molecular characterization of the MRSA isolate and medical record review for assessment of initial antimicrobial therapy were performed on a subset of patients. Among 2,636 patients with S. aureus SSTIs, the prevalence of CA-MRSA was 9% in 2004, 16% in 2005, and 21% in 2006 (P < 0.0001, chi-square test for trend). Seventy-five percent of CA-MRSA isolates tested were of the USA 300 or 400 clone type. Ninety-two percent of CA-MRSA isolates tested were positive for Panton-Valentine leukocidin, of which 90% carried staphylococcal chromosomal cassette mec type IV. The rate of use of a beta-lactam antibiotic as initial empirical therapy for patients with CA-MRSA SSTIs was 86%, 77%, and 60% in 2004, 2005, and 2006, respectively (P = 0.04, chi-square test for trend). Thirty percent of beta-lactam-treated patients had a documented risk factor for CA-MRSA infection. The use of a beta-lactam antibiotic as initial empirical therapy for CA-MRSA SSTIs has decreased significantly over the past 3 years. However, even as the prevalence of CA-MRSA SSTIs approaches 25%, the majority of patients are still receiving inactive antimicrobial therapy. Further evaluation of the outcomes associated with discordant therapy for CA-MRSA SSTIs is needed.

Role of previous hospitalization in clinically-significant MRSA infection among HIV-infected inpatients: results of a case-control study

Background

HIV-infected subjects have high incidence rates of Staphylococcus aureus infections, with both methicillin-susceptible and methicillin-resistant (MRSA) strains. Possible explanations could include the high burden of colonization, the behavioral risk factors, and the frequent exposures to health care facilities of HIV-infected patients. The purpose of the study was to assess the risk factors for clinically- significant methicillin-resistant Staphylococcus aureus (CS-MRSA) infections in HIV-infected patients admitted to Infectious Diseases Units.

Methods

From January 1, 2002 to December 31, 2005, we conducted a retrospective case-control (1:2) study. We identified all the cases of CS-MRSA infections in HIV-infected patients admitted to the National Institute for Infectious Diseases (INMI) "Lazzaro Spallanzani" in the 4-year study period. A conditional logistic regression model was used to identify risk factors for CS-MRSA infection.

Results

We found 27 CS-MRSA infections, i.e. 0.9 CS-MRSA infections per 100 HIV-infected individuals cared for in our Institute. At multivariate analysis, independent predictors of CS-MRSA infection were cumulative hospital stay, invasive procedures in the previous year, and low CD4 cell count. Particularly, the risk for CS-MRSA increased by 14% per an increase of 5 days hospitalization in the previous year. Finally, we identified a low frequency of community-acquired MRSA infections (only 1 of 27; 3.7%) among HIV-infected patients.

Conclusion

Clinicians should be aware of the risk for CS-MRSA infection in the clinical management of HIV-infected patients, especially in those patients with a low CD4 cell count, longer previous hospital stay, and previous invasive procedures.

Community-acquired methicillin-resistant Staphylococcus aureus

Published data confirm that community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections are increasing in incidence in both urban and rural settings. The statistical risk is higher for athletes, military personnel, prison inmates, intravenous drug abusers, the homeless, children in daycare, and certain Native American groups, but the infections are by no means restricted to these populations. Roughly 85% of the infections involve the skin and subcutaneous tissue, with the most common presentations being an abscess or folliculitis. The typical associated gene cassette is quite small and codes only for methicillin resistance. Abscesses generally respond to drainage.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should recognize groups at high risk for community-acquired MSRA infections and manage these infections appropriately.

Fluoroquinolones and risk for methicillin-resistant Staphylococcus aureus, Canada

Fluoroquinolones were associated with MRSA colonization and infection.

Receipt of fluoroquinolones was the predominant risk factor for Clostridium difficile–associated disease (CDAD) during an epidemic in Quebec, Canada. To determine the role of antimicrobial drugs in facilitating healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) colonization and infection and to compare this role with their effects on methicillin-susceptible S. aureus infection and CDAD, we conducted a retrospective cohort study of patients in a Quebec hospital. For 7,371 episodes of care, data were collected on risk factors, including receipt of antimicrobial drugs. Crude and adjusted hazard ratios (AHR) were calculated by Cox regression. Of 150 episodes of MRSA colonization and 23 of MRSA infection, fluoroquinolones were the only antimicrobials that increased risk for colonization (AHR 2.57, 95% confidence interval [CI] 1.84–3.60) and infection (AHR 2.49, 95% CI 1.02–6.07). Effect of antimicrobial drugs on MRSA colonization and infection was similar to effect on CDAD and should be considered when selecting antimicrobial drugs to treat common infections.

Treatment and outcomes of infections by methicillin-resistant Staphylococcus aureus at an ambulatory clinic

Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) skin and soft tissue infections (SSTI) have become increasingly common. This study's objectives were to describe the clinical spectrum of MRSA in a community health center and to determine whether the use of specific antimicrobials correlated with increased probability of clinical resolution of SSTI. A retrospective chart review of 399 sequential cases of culture-confirmed S. aureus SSTI, including 227 cases of MRSA SSTI, among outpatients at Fenway Community Health (Boston, MA) from 1998 to 2005 was done. The proportion of S. aureus SSTI due to MRSA increased significantly from 1998 to 2005 (P<0.0001). Resistance to clindamycin was common (48.2% of isolates). At the beginning of the study period, most patients with MRSA SSTI empirically treated with antibiotics received a beta-lactam, whereas by 2005, 76% received trimethoprim-sulfamethoxazole (TMP-SMX) (P<0.0001). Initially, few MRSA isolates were sensitive to the empirical antibiotic, but 77% were susceptible by 2005 (P<0.0001). A significantly higher percentage of patients with MRSA isolates had clinical resolution on the empirical antibiotic by 2005 (P=0.037). Use of an empirical antibiotic to which the clinical isolate was sensitive was associated with increased odds of clinical resolution on empirical therapy (odds ratio=5.91), controlling for incision and drainage and HIV status. MRSA now accounts for the majority of SSTI due to S. aureus at Fenway, and improved rates of clinical resolution on empirical antibiotic therapy have paralleled increasing use of empirical TMP-SMX for these infections. TMP-SMX appears to be an appropriate empirical antibiotic for suspected MRSA SSTI, especially where clindamycin resistance is common.

Community-associated methicillin-resistant Staphylococcus aureus in the patient with HIV infection

The prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has increased alarmingly in both the general population and the HIV-infected community. We look at the background of MRSA including the mechanisms of resistance, genetics, and trends in the individual with HIV infection. Numerous studies have investigated the risk factors for CA-MRSA. Other studies have further characterized the incidence of and risk factors for MRSA infections in the HIV community. Although one might not readily associate advanced HIV infection with increased susceptibility to bacterial pathogens, a number of studies have explained the mechanisms of this B-cell-mediated susceptibility. Invasive MRSA infections have spread into communities, are increasingly prevalent, and pose a public health challenge for their containment, prevention, and treatment.

Septic arthritis in patients with human immunodeficiency virus

The literature contains few descriptions of the infective organisms and diagnostic issues associated with musculoskeletal infections in patients with HIV. We retrospectively reviewed 19 patients with HIV treated at our musculoskeletal infection ward for septic arthritis. The mean CD4 count was 154/mm (range, 7-482/mm), and 11 patients had a CD4 count < 200/mm and were diagnosed with AIDS. The most common pathogen (six patients) was oxacillin-resistant Staphylococcus aureus. Mycobacterial infections occurred in three patients but no fungal pathogens were identified. Septic arthritis was monoarticular in 14 patients and involved the knee in eight patients, the hip in three patients, and the wrist in three patients. Five patients presented with polyarticular septic arthritis. All mycobacterial infections and four of the five polyarticular infections occurred in patients with a CD4 count < 200/mm. Patients with CD4 count < 200/mm had a lower joint fluid WBC count compared to patients with a CD4 count > 200/mm (40,500 vs 69,000/mm). Oxacillin-resistant Staphylococcus aureus was the most common pathogen. A high index of suspicion for Mycobacterium. tuberculosis arthritis and polyarticular septic arthritis is necessary in patients with HIV and a CD4 count < 200/mm.

Cutaneous Infections Associated with HIV/AIDS

With diminished and dysregulated cell-mediated immunity, HIV-infected individuals are susceptible to a myriad of skin infections. These infections include the conditions encountered in immunocompetent patients, as well as infections seen almost exclusively in the setting of HIV infection. The HIV/AIDS pandemic has made some previously rare infections more prominent. Although antiretroviral therapy has been helpful in relieving the burden of cutaneous infections in HIV-infected patients, it does not prevent all opportunistic infections in the skin and also has created new dilemmas.

Community-onset methicillin-resistant Staphylococcus aureus in an urban HIV clinic

OBJECTIVES

To determine the proportion of skin/soft tissue infections (SSTIs) and to determine risks for MRSA infection caused by methicillin-resistant Staphylococcus aureus (MRSA) in HIV-infected out-patients.

METHODS

We conducted a prospective study of SSTIs in HIV-infected out-patients. A questionnaire was used to record MRSA risk factors and treatment. In vitro testing for antibiotic susceptibility, inducible clindamycin resistance, panton-valentine leucocidin (PVL) toxin, and the staphylococcal chromosomal cassette mec (SCCmec) type was performed using standardized methods. Treatment outcomes included resolution of primary site of infection, nonresolution of infection and reinfection and were confirmed at clinic visit and/or telephone follow-up.

RESULTS

Forty-one of 44 patients had an SSTI caused by MRSA. African-Americans comprised 21 of 41 MRSA patients. The median CD4 count of MRSA patients was 411 cells/microL. Four patients required hospitalization and three patients had secondary bacteraemia. Twenty-one of 41 MRSA patients had healthcare-associated (HCA) MRSA risk factors including a history of prior MRSA infection (n=9) and hospitalization within 6 months (n=11). Other prevalent MRSA risk factors included receipt of systemic antibiotics within 6 months (n=21) and previous incarceration (n=19). Twenty-two patients had a significant non-HIV-related comorbid illness. The majority of isolates were susceptible to trimethoprim-sulfamethoxazole, tetracycline, and clindamycin. Inducible clindamycin resistance was detected in 0 of 16 erythromycin-resistant, clindamycin-susceptible MRSA isolates. Twenty-one of 24 isolates tested positive for SCCmec type IV. Twenty-four of 24 isolates tested positive for the PVL gene. Antibiotic treatment was discordant (bacteria nonsusceptible to antibiotic used) in eight MRSA patients. The primary SSTI resolved in 37 of 40 MRSA patients. Recurrence of infection at a site other than the primary site was relatively common (11 patients).

CONCLUSIONS

We found a high rate of MRSA causing SSTI in community-dwelling patients. The majority of isolates were positive for PVL and SCCmec IV, which is typical of community-associated MRSA isolates causing SSTIs in the general population. Inducible clindamycin resistance was not detected. Most patients had MRSA risk factors. The initial site of infection resolved in most cases but subsequent MRSA infection was relatively common.

Management of patients with HIV in the intensive care unit

Because there are more than one million Americans with HIV, intensive care units continue to see frequent patients with HIV infection. In the era of highly active antiretroviral therapy, clinicians must be aware of drug toxicities and drug interactions. They must also recognize traditional opportunistic infections, as well as newer syndromes such as immune reconstitution syndrome, multicentric Castleman's disease, and primary pleural cell lymphoma.