Necrotizing pneumonia and septic shock: suspecting CA-MRSA in patients presenting to Canadian emergency departments

Is there still a role for vancomycin in skin and soft-tissue infections?

PURPOSE OF REVIEW

Skin and soft-tissue infections (SSIs) are among the commonest infections encountered in clinical practice. Spread of methicillin-resistant Staphylococcus aureus SSIs continues to increase in both health care and community settings and presents a challenge for the best treatment choice. Vancomycin has been the mainstay of SSIs treatment, but recently its use has been questioned because of concerns about its efficacy, tolerability, and unfavorable pharmacokinetic/pharmacodynamic profile. The purpose of this review is to establish the current role for vancomycin in light of the literature published from January 2007 to September 2017 on comparison with both old and new alternatives.

RECENT FINDINGS

Meta-analyses show better clinical and microbiological outcomes for drugs approved for the treatment of SSI, including those sustained by methicillin-resistant S. aureus, in the last 10 years than for vancomycin. The newer glycopeptides and linezolid decrease the total treatment costs compared with vancomycin, by reducing the length of stay or avoiding the hospitalization.

SUMMARY

Vancomycin is noninferior in efficacy and safety to all comparator drugs, including the newest on the market. However, the SSI treatment evidence base presents several shortcomings limiting the clinical applicability of the results. High-level clinical trials should be performed to obtain results that can be generalized and applied effectively in clinical practice.

Macrophage-derived LTB4 promotes abscess formation and clearance of Staphylococcus aureus skin infection in mice

The early events that shape the innate immune response to restrain pathogens during skin infections remain elusive. Methicillin-resistant Staphylococcus aureus (MRSA) infection engages phagocyte chemotaxis, abscess formation, and microbial clearance. Upon infection, neutrophils and monocytes find a gradient of chemoattractants that influence both phagocyte direction and microbial clearance. The bioactive lipid leukotriene B4 (LTB4) is quickly (seconds to minutes) produced by 5-lipoxygenase (5-LO) and signals through the G protein-coupled receptors LTB4R1 (BLT1) or BLT2 in phagocytes and structural cells. Although it is known that LTB4 enhances antimicrobial effector functions in vitro, whether prompt LTB4 production is required for bacterial clearance and development of an inflammatory milieu necessary for abscess formation to restrain pathogen dissemination is unknown. We found that LTB4 is produced in areas near the abscess and BLT1 deficient mice are unable to form an abscess, elicit neutrophil chemotaxis, generation of neutrophil and monocyte chemokines, as well as reactive oxygen species-dependent bacterial clearance. We also found that an ointment containing LTB4 synergizes with antibiotics to eliminate MRSA potently. Here, we uncovered a heretofore unknown role of macrophage-derived LTB4 in orchestrating the chemoattractant gradient required for abscess formation, while amplifying antimicrobial effector functions.

Fulminant necrotising fasciitis by community-acquired methicillin-resistant Staphylococcus aureus

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is a rare cause of necrotising fasciitis (NF), and is usually not fulminant as in group A Streptococcus (GAS), the archetypal aetiology. We report an unusually fulminant case of NF by CA-MRSA in an immunocompetent patient. A 52-year-old man presented to the emergency department with 1 week of progressive left thigh pain and swelling. The patient had ecchymoses, bullae and hypoesthesia of the involved skin, and CT scan revealed extensive fascial oedema. He was immediately started on broad spectrum antibiotics. Within 12 h of presentation, he underwent surgical debridement. Despite aggressive supportive care, the patient died less than 24 h after presentation. MRSA, with an antibiogram suggestive of a community-acquired strain, was recovered from intraoperative specimens and admission blood cultures. This case underscores that CA-MRSA, while rarely reported, can cause a fulminant presentation of NF similar to GAS in immunocompetent patients.

Community acquired pneumonia with shock, severe hypoxemia and leucopenia: Is the etiology methicillin resistant Staphylococci?

A young, male presented to the emergency department with respiratory signs and symptoms along with shock and leucopenia. The suspected diagnosis of methicillin resistant Staphylococcus aureus (MRSA) necrotizing pneumonia was confirmed later radiographically and microbiologically. This entity is common in childhood, but rarely reported in adults. This form of pneumonia affects young individuals without any comorbid illness. This is the first reported case of necrotizing pneumonia caused by community acquired-MRSA from Indian subcontinent. The probability to predict etiology of pneumonia from clinical signs is low; yet in the presence of shock, severe hypoxemia and leucopenia suspicion of MRSA should be kept high and hence that prompt initiation of appropriate antimicrobials may reduce mortality.

Community-associated methicillin-resistant Staphylococcus aureus necrotizing pneumonia without evidence of antecedent viral upper respiratory infection

BACKGROUND

USA300 community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) strains causing necrotizing pneumonia have been reported in association with antecedent viral upper respiratory tract infections (URI).

METHODS

A case series of necrotizing pneumonia presenting as a primary or coprimary infection, secondary to CA-MRSA without evidence of antecedent viral URI, is presented. Cases were identified through the infectious diseases consultation service records. Clinical and radiographic data were collected by chart review and electronic records. MRSA strains were isolated from sputum, bronchoalveolar lavage, pleural fluid or blood cultures and confirmed using standard laboratory procedures. MRSA strains were characterized by susceptibility testing, pulsed-field gel electrophoresis, spa typing, agr typing and multilocus sequence typing. Testing for respiratory viruses was performed by appropriate serological testing of banked sera, or nucleic acid testing of nasopharyngeal or bronchoalveloar lavage specimens.

RESULTS

Ten patients who presented or copresented with CA necrotizing pneumonia secondary to CA-MRSA from April 2004 to October 2011 were identified. The median length of stay was 22.5 days. Mortality was 20.0%. Classical risk factors for CA-MRSA were identified in seven of 10 (70.0%) cases. Chest tube placement occurred in seven of 10 patients with empyema. None of the patients had historical evidence of antecedent URI. In eight of 10 patients, serological or nucleic acid testing testing revealed no evidence of acute viral coinfection. Eight strains were CMRSA-10 (USA300). The remaining two strains were a USA300 genetically related strain and a USA1100 strain.

CONCLUSION

Pneumonia secondary to CA-MRSA can occur in the absence of an antecedent URI. Infections due to CA-MRSA are associated with significant morbidity and mortality. Clinicians need to have an awareness of this clinical entity, particularly in patients who are in risk groups that predispose to exposure to this bacterium.

Pathogenesis of Staphylococcus aureus necrotizing pneumonia: the role of PVL and an influenza coinfection

Only recently necrotizing pneumonia was defined as a specific disease entity that is caused by a Panton-Valentine leukocidin (PVL)-producing Staphylococcus aureus strain and is frequently preceded by an influenza infection. Necrotizing pneumonia is characterized by a sudden onset and rapid worsening of symptoms, leukopenia, airway hemorrhages, severe respiratory failure and a high mortality rate. Despite clear epidemiological data, the function of PVL in necrotizing pneumonia has been controversially discussed due to conflicting results from different disease models. Furthermore, there are many proposed mechanisms how a viral infection could facilitate and interact with a bacterial superinfection. In this review, we summarize current data from 43 clinical cases and results from various infection models on necrotizing pneumonia. We discuss the contribution of S. aureus PVL and a preceding influenza infection and present a concept of the pathogenesis of necrotizing pneumonia.

High rates of Staphylococcus aureus USA400 infection, Northern Canada

Surveillance of Staphylococcus aureus infections in 3 northern remote communities of Saskatchewan was undertaken. Rates of methicillin-resistant infections were extremely high (146–482/10,000 population), and most (98.2%) were caused by USA400 strains. Although USA400 prevalence has diminished in the United States, this strain is continuing to predominate throughout many northern communities in Canada.

Factors associated with the outcome of life-threatening necrotizing pneumonia due to community-acquired Staphylococcus aureus in adult and adolescent patients

BACKGROUND

Although community-acquired Staphylococcus aureus pneumonia with highly virulent Panton-Valentine leukocidin (PVL)-positive strains, a severe disease with significant lethality, is rare, especially in adult and adolescent patients, recent reports highlight that these infections are on the rise.

OBJECTIVES

To describe the demographic and clinical features of reported cases of life-threatening community-acquired S. aureus pneumonia with usually PVL-positive strains in adult and adolescent patients, to evaluate the variables related to death, and to select a more appropriate antimicrobial treatment for this potentially deadly disease.

METHODS

We summarized all of the 92 reported cases and our case. The effect of 5 variables on mortality was measured using logistic regression.

RESULTS

S. aureus community-acquired pneumonia (CAP) with usually PVL-positive strains is a severe disease with significant lethality, i.e. 42.9%; a short duration of the time from the onset of symptoms to death, i.e. 5.5 ± 10.1 days, and prolonged hospital admissions, i.e. 33.2 ± 29.5 days. Seventy-three cases have been tested for the gene for PVL, and 71 strains have been found to carry the PVL gene. Logistic regression analysis showed that leucopenia (p = 0.002), influenza-like symptoms or laboratory-confirmed influenza (p = 0.011), and hemoptysis (p = 0.024) were the factors associated with death. Antibiotic therapies inhibiting toxin production were associated with an improved outcome in these cases (p = 0.007).

CONCLUSIONS

Physicians should pay special attention to those patients who acquired severe CAP during influenza season and have flu-like symptoms, hemoptysis, and leucopenia, and they should consider S. aureus more frequently among the possible pathogens of severe CAP. Empiric therapy for severe CAP with this distinct clinical picture should include coverage for S. aureus. Targeted treatment with antimicrobials inhibiting toxin production appears to be a more appropriate selection.

Prevalence of USA300 strain type of methicillin-resistant Staphylococcus aureus among patients with nasal colonization identified with active surveillance

BACKGROUND

USA300 is the most prevalent strain type of community-acquired methicillin-resistant Staphylococcus aureus (MRSA), but the proportion of patients colonized with USA300 strains and their risk for infection are largely unknown.

OBJECTIVE

To determine the prevalence of USA300 strains among MRSA nasal colonizing isolates in our hospital, to identify risks for USA300 nasal colonization, and to determine risks of developing infection for nasally colonized patients.

METHODS

Retrospective cohort study of patients found to be nasally colonized with MRSA through active surveillance at a tertiary care hospital from January 2005 through December 2007. MRSA isolates were identified as USA300 or non-USA300. Risks for colonization and infection were identified with logistic regression.

RESULTS

Among 1,306 MRSA nasal isolates, 307 (24%) were USA300 strains, and this proportion significantly increased over time (17.4% in 2005 and 26.7% in 2007; P = .003). African American race was an independent risk for USA300 nasal colonization (odds ratio [OR], 1.81 [95% confidence ratio {CI}, 1.38-2.38]). Older age (OR, 0.97 [95% CI, 0.96-0.98]) and female sex (OR, 0.74 [95% CI, 0.56-0.97]) decreased risk. Among nasally colonized patients, 238 (18.2%) developed infection. Increased length of stay (OR, 1.03 [95% CI, 1.01-1.06]) independently increased risk for infection among patients nasally colonized with USA300 MRSA, and female sex decreased risk (OR, 0.48 [95% CI, 0.24-0.95]). Increased length of stay (OR, 1.03 [95% CI, 1.02-1.04]) and treatment in an intensive care unit (OR, 1.64 [95% CI, 1.10-2.44]) independently increased risk for infection among patients nasally colonized with non-USA300 MRSA, and female sex decreased risk (OR, 0.67 [95% CI, 0.47-0.94]).

CONCLUSION

The proportion of MRSA nasally colonized patients with USA300 strains significantly increased during the study, and risks included African American race. Strain type had no significant effect on the proportion of patients who developed infection, and risk factors for infection were similar.

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.

The Panton-Valentine leukocidin vaccine protects mice against lung and skin infections caused by Staphylococcus aureus USA300

Methicillin-resistant Staphylococcus aureus is increasingly responsible for staphylococcal infections in the community. A large percentage of the community-acquired methicillin-resistant (CA-MRSA) strains in the USA produce Panton-Valentine leukocidin (PVL), which is associated with severe infections. The virulence of the clinical CA-MRSA strain USA300 was compared to that of its isogenic pvl-deleted mutant, and it was shown that PVL contributes to lung and muscle tissue destruction, respectively, in murine necrotizing pneumonia and skin infection models. Mice infected with the USA300 strain developed a dominant anti-PVL response. The PVL subunits were therefore tested as vaccinogens against this isolate, and their vaccine efficacy correlated with both the route of vaccination and infection. These data suggest that PVL is a virulence factor in murine CA-MRSA infections.

Community-Associated Methicillin-Resistant Staphylococcus aureus in the Pediatric Population

PURPOSE

To review the epidemiology and prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), define the differences between community-acquired and hospital-acquired strains, highlight the advantages and disadvantages of antibiotics commonly used to treat infections caused by this pathogen, and identify strategies to limit the spread of this organism and prevent future outbreaks.

DATA

Literature was accessed through MEDLINE using the search terms community-acquired methicillin-resistant Staphylococcus aureus, community-associated methicillin-resistant Staphylococcus aureus, CA-MRSA, pediatrics, and children. Articles evaluated were published in the English language and limited to human studies. References of literature identified by initial search techniques were reviewed for additional relevant articles.

DATA SYNTHESIS

Community-associated methicillin-resistant Staphylococcus aureus has become a prominent pathogen in pediatric patients in the last ten years. Its increasing prevalence has been reported throughout the United States, and it is the cause of over one half of all skin and soft tissue infections seen in many hospitals and emergency departments. The risk factors for infection with this pathogen differ from those associated with hospital-acquired strains. Mild to moderate infections can generally be treated with oral antibiotics, while more serious infections may require parenteral therapy. Sulfamethoxazole/trimethoprim and clindamycin are the preferred oral agents due to their efficacy, tolerability, well established side effect profiles, and cost. Vancomycin is the standard of care for parenteral therapy, although clindamycin is an acceptable parenteral alternative. More costly agents such as linezolid, daptomycin, and quinupristin/dalfopristin should be reserved for patients with severe infections, multiple allergies, or in strains with unusual resistance patterns. The best way to prevent and control outbreaks is to maintain standard infection control procedures including excellent hand hygiene.

CONCLUSIONS

CA-MRSA is a serious and frequently seen pathogen. Proper antibiotic selection that takes into account patient factors, disease severity, ease of administration, and cost is necessary to maximize favorable patient outcomes.

Severe necrotizing fasciitis in a human immunodeficiency virus-positive patient caused by methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a rarely reported cause of necrotizing fasciitis. We report an unusually severe case of MRSA necrotizing fasciitis in a previously undiagnosed AIDS patient. Molecular analysis revealed that the strain had the USA300/spa1 genotype, now an abundant cause of community-acquired MRSA infection.