Epidemiology of methicillin-resistant Staphylococcus aureus at a pediatric healthcare system, 1991-2003

Clinical Practice Guideline by the Pediatric Infectious Diseases Society and the Infectious Diseases Society of America: 2021 Guideline on Diagnosis and Management of Acute Hematogenous Osteomyelitis in Pediatrics

This clinical practice guideline for the diagnosis and treatment of acute hematogenous osteomyelitis (AHO) in children was developed by a multidisciplinary panel representing Pediatric Infectious Diseases Society (PIDS) and the Infectious Diseases Society of America (IDSA). This guideline is intended for use by healthcare professionals who care for children with AHO, including specialists in pediatric infectious diseases, orthopedics, emergency care physicians, hospitalists, and any clinicians and healthcare providers caring for these patients. The panel's recommendations for the diagnosis and treatment of AHO are based upon evidence derived from topic-specific systematic literature reviews. Summarized below are the recommendations for the diagnosis and treatment of AHO in children. The panel followed a systematic process used in the development of other IDSA and PIDS clinical practice guidelines, which included a standardized methodology for rating the certainty of the evidence and strength of recommendation using the GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach. A detailed description of background, methods, evidence summary and rationale that support each recommendation, and knowledge gaps can be found online in the full text.

Methicillin-Resistant Staphylococcus aureus: Molecular Characterization, Evolution, and Epidemiology

Staphylococcus aureus, a major human pathogen, has a collection of virulence factors and the ability to acquire resistance to most antibiotics. This ability is further augmented by constant emergence of new clones, making S. aureus a "superbug." Clinical use of methicillin has led to the appearance of methicillin-resistant S. aureus (MRSA). The past few decades have witnessed the existence of new MRSA clones. Unlike traditional MRSA residing in hospitals, the new clones can invade community settings and infect people without predisposing risk factors. This evolution continues with the buildup of the MRSA reservoir in companion and food animals. This review focuses on imparting a better understanding of MRSA evolution and its molecular characterization and epidemiology. We first describe the origin of MRSA, with emphasis on the diverse nature of staphylococcal cassette chromosome mec (SCCmec). mecA and its new homologues (mecB, mecC, and mecD), SCCmec types (13 SCCmec types have been discovered to date), and their classification criteria are discussed. The review then describes various typing methods applied to study the molecular epidemiology and evolutionary nature of MRSA. Starting with the historical methods and continuing to the advanced whole-genome approaches, typing of collections of MRSA has shed light on the origin, spread, and evolutionary pathways of MRSA clones.

Characteristics and risk factors of hospital acquired - Methicillin-resistant Staphylococcus aureus (HA-MRSA) infection of pediatric patients in a tertiary care hospital in Riyadh, Saudi Arabia

Background and objectives

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) infections has been steadily increasing. These infections are considered to be either hospital-acquired MRSA (HA-MRSA) or community-acquired MRSA (CA-MRSA). Children are at higher risk of infection than adults. HA-MRSA has been reported to have more serious outcomes than CA-MRSA. However, there are not enough studies in Saudi Arabia to study the characteristics of HA-MRSA in children. We aim to describe the characteristics of HA-MRSA infection, including risk factors, culture site, clinical manifestations, complications, and outcomes among pediatric patients in a tertiary care hospital in Riyadh, Saudi Arabia.

Design and settings

This is a retrospective chart review study. It was conducted in King Abdulaziz medical city in Riyadh.

Patients and methods

The study included all patients 14 years of age or younger who were culture-positive from any site in the body during the period from January 1, 2009 to December 31, 2011. The time of culture compared to admission time was used to differentiate between CA-MRSA (within 72 h of admission) and HA-MRSA (more than 72 h after admission). The final sample size was 39 patients.

Results

We found HA-MRSA to be more common in males and those with risk factors such as previous surgery and previous hospitalization. Patients had a high Pediatric intensive care unit (PICU) admission rate and were commonly septic with positive blood cultures. Seventy-four percent of patients fully recovered, 10% recovered with complications and 15% died.

Conclusion

HA-MRSA is an infection that can cause serious complications and a high rate of PICU admissions. Clinical manifestations such as shock are associated with higher mortality and morbidity rates. Special care should be given to those admitted to PICU, as they have high rates of mortality and morbidity.

Treatment Failure Outcomes for Emergency Department Patients with Skin and Soft Tissue Infections

Introduction

Skin and soft tissue infections (SSTIs) are commonly evaluated in the emergency department (ED). Our objectives were to identify predictors of SSTI treatment failure within one week post-discharge in patients with cutaneous abscesses, as well as to identify predictors of recurrence within three months in that proportion of participants.

Methods

This was a sub-analysis of a parent study, conducted at two EDs, evaluating a new, nucleic acid amplification test (NAAT) for Staphylococcus aureus in ED patients. Patients ≥18 years receiving incision and drainage (I&D) were eligible. Patient-reported outcome data on improvement of fever, swelling, erythema, drainage, and pain were collected using a structured abstraction form at one week, one month, and three months post ED visit.

Results

We enrolled 272 participants (20 from a feasibility study and 252 in this trial), of which 198 (72.8%) completed one-week follow up. Twenty-seven additional one-week outcomes were obtained through medical record review rather than by the one-week follow-up phone call. One hundred ninety-three (73%) patients completed either the one- or three-month follow up. Most patients recovered from their initial infection within one week, with 10.2% of patients reporting one-week treatment failure. The odds of treatment failure were 66% lower for patients who received antibiotics following I&D at their initial visit. Overall SSTI recurrence rate was 28.0% (95% CI [21.6%–34.4%]) and associated with contact with someone infected with methicillin resistant S. aureus (MRSA), previous SSTI history, or clinician use of wound packing.

Conclusion

Treatment failure was reduced by antibiotic use, whereas SSTI recurrence was associated with prior contact, SSTI, or use of packing.

Community-associated methicillin-resistant Staphylococcus aureus in a pediatric emergency department in Newfoundland and Labrador

BACKGROUND

First-generation cephalosporins and antistaphylococcal penicillins are typically the first choice for treating skin and soft tissue infections (SSTI), but are not effective for infections caused by methicillin-resistant Staphylococcus aureus (MRSA). It is currently unclear what percentage of SSTIs is caused by community-associated MRSA in different regions in Canada.

OBJECTIVES

To determine the incidence of MRSA in children presenting to a pediatric emergency department with SSTI, and to determine which antibiotics were used to treat these infections.

METHODS

All visits to a pediatric emergency department were reviewed from April 15, 2010 to April 14, 2011. Diagnoses of cellulitis, abscess, impetigo, folliculitis and skin infection (not otherwise specified) were reviewed in detail to determine whether a culture was taken and which antibiotic was prescribed.

RESULTS

There were 367 cases of SSTI diagnosed over the study period. Forty-five (12.3%) patients had lesions that were swabbed for culture and sensitivity. S aureus was the most common organism found, with 14 (66%) methicillin-sensitive cases and seven (33%) methicillin-resistant cases. Of the seven cases of MRSA identified, only one patient had clear risk factors for hospital-acquired MRSA. First-generation cephalosporins were initially prescribed for 280 (76%) patients.

CONCLUSIONS

The overall incidence of MRSA in the population presenting to a pediatric emergency department in Newfoundland and Labrador appeared to be low, although only a small percentage of infections were cultured. At this time, there appears to be no need to change empirical antibiotic coverage, which remains a first-generation cephalosporin.

The impact of evidence-based clinical practice guidelines applied by a multidisciplinary team for the care of children with osteomyelitis

BACKGROUND

Care of children with osteomyelitis requires multidisciplinary collaboration. This study evaluates the impact of evidence-based guidelines for the treatment of pediatric osteomyelitis when utilized by a multidisciplinary team.

METHODS

Guidelines for pediatric osteomyelitis were developed and were implemented by a multidisciplinary team comprised of individuals from several hospital services, including orthopaedics, pediatrics, infectious disease, nursing, and social work, who met daily to conduct rounds and make treatment decisions. With use of retrospective review and statistical analysis, we compared children with osteomyelitis who had been managed at our institution from 2002 to 2004 (prior to the implementation of the guidelines), referred to as Group I in this study, with those who were managed in 2009 according to the guidelines, referred to as Group II.

RESULTS

Two hundred and ten children in Group I were compared with sixty-one children in Group II. No significant differences between the two cohorts were noted for age, sex, incidence of methicillin-resistant Staphylococcus aureus infection (18.1% in Group I compared with 26.2% in Group II), incidence of methicillin-sensitive Staphylococcus aureus infection (23.8% in Group I compared with 27.9% in Group II), bacteremia, or surgical procedures. Significant differences (p < 0.05) between cohorts were noted for each of the following: the delay in magnetic resonance imaging after admission (2.5 days in Group I compared with one day in Group II), the percentage of patients who had received clindamycin as the initial antibiotic (12.9% in Group I compared with 85.2% in Group II), the percentage of patients who had had a blood culture before antibiotic administration (79.5% in Group I compared with 91.8% in Group II), the percentage of patients who had had a culture of tissue from the infection site (62.9% in Group I compared with 78.7% in Group II), the percentage of patients in whom the infecting organism was identified on tissue or blood culture (60.0% in Group I compared with 73.8% in Group II), the number of antibiotic changes (2.0 changes in Group I compared with 1.4 changes in Group II), and the mean duration of oral antibiotic use (27.7 days in Group I compared with 43.7 days in Group II). When compared with Group I, Group II had clinically important trends of a shorter total length of hospital stay (12.8 days in Group I compared with 9.7 days in Group II; p = 0.054) and a lower hospital readmission rate (11.4% in Group I compared with 6.6% in Group II; p = 0.34).

CONCLUSIONS

Evidence-based treatment guidelines applied by a multidisciplinary team resulted in a more efficient diagnostic workup, a higher rate of identifying the causative organism, and improved adherence to initial antibiotic recommendations with fewer antibiotic changes during treatment. Additionally, there were trends toward lower hospital readmission rates and a shorter length of hospitalization.

Epidemics of community-associated methicillin-resistant Staphylococcus aureus in the United States: a meta-analysis

Staphylococcus aureus is the most frequent cause of skin and soft tissue infections in humans. Methicillin-resistant strains of S. aureus (MRSA) that emerged in the 1960s presented a relatively limited public health threat until the 1990s, when novel community-associated (CA-) MRSA strains began circulating. CA-MRSA infections are now common, resulting in serious and sometimes fatal infections in otherwise healthy people. Although some have suggested that there is an epidemic of CA-MRSA in the U.S., the origins, extent, and geographic variability of CA-MRSA infections are not known. We present a meta-analysis of published studies that included trend data from a single site or region, and derive summary epidemic curves of CA-MRSA spread over time. Our analysis reveals a dramatic increase in infections over the past two decades, with CA-MRSA strains now endemic at unprecedented levels in many US regions. This increase has not been geographically homogeneous, and appears to have occurred earlier in children than adults.

National surveillance of methicillin-resistant Staphylococcus aureus among hospitalized pediatric patients in Canadian acute care facilities, 1995-2007

BACKGROUND

Information relating to the epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) among hospitalized pediatric patients is limited. This report describes results of national MRSA surveillance among Canadian hospitalized pediatric patients from 1995 to 2007.

METHODS

Surveillance was laboratory-based. Clinical and epidemiologic data were obtained by reviewing the medical records. Standardized definitions were used to determine MRSA infection. Isolates were characterized by pulsed-field gel electrophoresis, staphylococcal cassette chromosome mec typing and antimicrobial susceptibility testing.

RESULTS

A total of 1262 pediatric patients were newly identified as MRSA positive from 1995 to 2007. Ages ranged from newborn to 17.9 years, 49% were infected with MRSA (51% colonized), skin and soft tissue infections accounted for the majority (59%) of MRSA infections and 57% were epidemiologically classified as community acquired (CA). The most common epidemic strain types isolated were CMRSA2/USA100/800, CMRSA10/USA300 and CMRSA7/USA400. Overall, MRSA rates per 10,000 patient days increased from 0.08 to 3.88. Since 2005, overall rates of CA-MRSA per 10,000 patient days have dramatically increased while healthcare-associated MRSA rates remained relatively stable.

CONCLUSIONS

These data suggest that the increase in MRSA among hospitalized pediatric patients is largely driven by the emergence of CA-MRSA strains with skin and soft tissue infections representing the majority of MRSA infections.

Trends and characteristics of culture-confirmed Staphylococcus aureus infections in a large U.S. integrated health care organization

Infections due to Staphylococcus aureus present a significant health problem in the United States. Between 1990 and 2005, there was a dramatic increase in community-associated methicillin-resistant S. aureus (MRSA), but recent reports suggest that MRSA may be declining. We retrospectively identified S. aureus isolates (n = 133,450) that were obtained from patients in a large integrated health plan between 1 January 1998 and 31 December 2009. Trends over time in MRSA were analyzed, and demographic risk factors for MRSA versus methicillin-susceptible S. aureus (MSSA) were identified. The percentage of S. aureus isolates that were MRSA increased from 9% to 20% between 1998 and 2001 and from 25% to 49% between 2002 and 2005 and decreased from 49% to 43% between 2006 and 2009. The increase in MRSA was seen in blood and in other bacteriological specimens and occurred in all age and race/ethnicity groups, though it was most pronounced in persons aged 18 to <50 years and African-Americans. Hospital onset infections were the most likely to be MRSA (odds ratio [OR], 1.58; confidence interval [CI], 1.46 to 1.70, compared to community-associated cases), but the largest increase in MRSA was in community-associated infections. Isolates from African-Americans (OR, 1.73; CI, 1.64 to 1.82) and Hispanics (OR, 1.11; CI, 1.06 to 1.16) were more likely to be MRSA than those from whites. After substantial increases between 1998 and 2005 in the proportion of S. aureus isolates that were MRSA, the proportion decreased between 2006 and 2009. Hospital onset S. aureus infections are disproportionately MRSA, as are those among African-Americans.

Increasing national burden of hospitalizations for skin and soft tissue infections in children

BACKGROUND

The number of children requiring treatment of skin and soft tissue infections (SSTIs) has increased since the emergence of methicillin-resistant Staphylococcus aureus.

METHODS

The 2000, 2003, and 2006 Kids' Inpatient Databases were queried for patients with a primary diagnosis of SSTI. Weighted data were analyzed to estimate temporal changes in incidence, incision and drainage (I&D) rate, and economic burden. Factors associated with I&D were analyzed by multivariable logistic regression.

RESULTS

Pediatric SSTI admissions increased (1) in number, (2) as a fraction of all hospital admissions, and (3) in incidence per 100,000 children from the years 2000 (17,525 ± 838; 0.65%; 23.2) to 2003 (27,463 ± 1652; 0.99%; 36.2) and 2006 (48,228 ± 2223; 1.77%; 62.7). Children younger than 3 years accounted for 49.6% of SSTI admissions in 2006, up from 32.5% in 2000. Utilization of I&D increased during the study period from 26.0% to 43.8%. Factors most associated with requiring I&D were age less than 3 years and calendar year 2006 (both P < .001). Hospital costs per patient increased over time and were higher in the group of patients who required I&D ($4296 ± $84 vs $3521 ± $81; P < .001; year 2006). Aggregate national costs reached $184.0 ± $9.4 million in 2006.

CONCLUSION

The recent spike in pediatric SSTIs has disproportionately affected children younger than 3 years, and an increasing fraction of these children require I&D. The national economic burden is substantial.

Hospital-acquired Staphylococcus aureus infections at Texas Children's Hospital, 2001-2007

OBJECTIVE

To document the introduction of the methicillin-resistant Staphylococcus aureus (MRSA) USA300 clone into a children's hospital. Current molecular epidemiology of infections due to the USA300 strain of MRSA in the pediatric healthcare setting remains obscure.

DESIGN

Retrospective study of patients with hospital-acquired S. aureus infection during the period from August 1, 2001, through July 31, 2007, at Texas Children's Hospital in Houston.

METHODS

Patients with hospital-acquired S. aureus infection from whom an isolate was available for molecular analysis were included. Clinical information was obtained from patient medical records and the electronic hospital information system. S. aureus isolates underwent antimicrobial susceptibility testing, pulsed-field gel electrophoresis, and polymerase chain reaction testing for staphylococcal cassette chromosome (SCC) mec, agr, the diamine N-acetyltransferase gene, and the Panton-Valentine leukocidin genes (pvl).

RESULTS

Of 242 patients with hospital-acquired S. aureus infection, 147 (61%) had methicillin-susceptible S. aureus infection. Of the 95 MRSA isolates causing hospital-acquired infection, 69 (73%) were USA300 isolates, and that rate did not increase over time. Skin and soft tissue infection (P < .001), onset of infection less than 10 days after admission (P = .007), and lack of comorbidities (P < .001) were associated with hospital-acquired MRSA infection caused by the USA300 strain, compared with other isolates (hereafter referred to as non-USA300 isolates). Nine of 10 patients with a S. aureus infection at the time of death were infected with a non-USA300 strain. USA300 carried SCCmec IV, agr I, the diamine N-acetyl transferase gene, and pvl. USA300 isolates were more susceptible to clindamycin, gentamicin, and trimethoprim-sulfamethoxazole than were other non-USA300 isolates (P < .01).

CONCLUSIONS

In our patient population, the annual numbers of observed cases of hospital-acquired S. aureus infection have remained constant. USA300 was the most common clone and, compared with other non-USA300 MRSA isolates, was associated with skin and soft tissue infection, early onset of infection after admission, and greater susceptibility to antimicrobial agents.

Life-threatening infection due to community-acquired methicillin-resistant Staphylococcus aureus: case report and review

We report an unusual case of serious, multifocal, invasive infection due to community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) in a 10-year-old girl with favorable outcome. The child manifested femoral osteomyelitis, pyomyositis, deep femoral vein thrombosis, pneumonia, encephalopathy, and disturbances of almost all organs. She remained in a critical condition for a week. Fever persisted for 6 weeks and acute phase reactants remained increased for 6 months, necessitating a 7-month antistaphylococcal therapy with a glycopeptide and clindamycin. This led to resolution of infection-associated problems during the subsequent 36 months of follow-up. CA-MRSA strain isolated from the patient harbored both staphylococcal chromosomal cassette type IV (SCCmec type IV) and Panton-Valentine leukocidin genes. A literature review of serious CA-MRSA infections indicated that only a small minority of published cases had favorable outcome.

Pediatric and neonatal Staphylococcus aureus bacteremia: epidemiology, risk factors, and outcome

OBJECTIVE

To evaluate the impact of methicillin-resistant Staphylococcus aureus on the prevalence of S. aureus bloodstream infection among children.

METHODS

Retrospective analysis of demographic data, risk factors for infection, and clinical outcomes for children (age, less than 18 years) with S. aureus bacteremia hospitalized at a children's hospital during 2001-2006.

RESULTS

We identified 164 episodes of S. aureus bacteremia among 151 children. The prevalence of bacteremia due to methicillin-susceptible S. aureus during 2001-2003 was approximately the same as that during 2004-2006 (29 and 30 cases, respectively, per 10,000 hospitalized children [hereafter, "per 10,000 hospitalizations"]), but the prevalence of bacteremia due to methicillin-resistant S. aureus increased from 4 to 11 cases, respectively, per 10,000 hospitalizations (P=.015). A total of 48% of infections involved children who had S. aureus-positive blood cultures less than 3 days after hospital admission. Seventy-four percent of these children had a preexisting comorbidity. When the prevalence of S. aureus bacteremia was stratified by race, sex, or age, neonates hospitalized at birth and Hispanic children had significantly reduced risks of infection. Children younger than 1 year of age (excluding neonates hospitalized at birth) had an increased prevalence of hospital-onset S. aureus bacteremia. There was a disproportionate increase in the risk of S. aureus bacteremia for each additional week of hospitalization among children with hospital-onset S. aureus bacteremia. Children with methicillin-resistant S. aureus bacteremia had a longer hospital stay, were transferred to another facility at a greater rate than they were discharged home, and had a greater mortality rate, compared with children with methicillin-susceptible S. aureus bacteremia.

CONCLUSION

This study documents the prevalence of S. aureus bacteremia among children with a high risk for acquiring this infection, and it describes populations of children who are at higher risk for bacteremia due to either methicillin-susceptible or methicillin-resistant S. aureus. Methods to improve prevention of S. aureus bacteremia are needed for children with healthcare-associated risk factors for S. aureus bacteremia.

Caenorhabditis elegans as a host model for community-associated methicillin-resistant Staphylococcus aureus

The nematode Caenorhabditis elegans has recently been developed as a host model for the study of Staphylococcus aureus virulence and pathogenesis. Here, the toxicity and virulence of representative clinical isolates of our methicillin-resistant S. aureus (MRSA) epidemic strains were studied using this model. The strains USA300 (associated with community infection outbreaks), USA400 (associated with sporadic community infections) and CMRSA2 (associated with both hospital and community infections), as well as the nematocidal reference strain NCTC8325, showed high nematocidal activity, both by killing the majority of the nematodes (> 90%) over 9 days, and by inhibiting second-generation nematode growth. By contrast, the typical hospital-associated MRSA strain CMRSA6, the colonization strain M92, and the non-pathogenic Staphylococcus epidermidis control strain ATCC12228 were non-toxic to the nematode, which behaved normally. The absence of nematocidal activity does not reflect lack of growth or reduced growth of the bacterial inoculum. The two non-nematocidal strains share similar genomic backgrounds, bacterial growth curve patterns and virulence gene profiles. However, the nematocidal strains each showed the same low maximum density growth curve patterns, but possessed distinct genetic profiles; no common virulence gene patterns or specific genes have been elucidated. Our findings demonstrate that community-associated MRSA strains are more pathogenic than hospital-associated MRSA in the C. elegans model and support the use of this model for studying the virulence of S. aureus strains.

Staphylococcus aureus: a community pathogen

Staphylococcus aureus is a common human pathogen. S aureus infections most commonly clinically manifest as skin infections. There has been much interest in S aureus infections in the community over the past decade because of the rise of community-associated methicillin-resistant S aureus (CA-MRSA) infections, which have emerged globally over a relatively short period of time. In contrast to health care-associated methicillin resistant S aureus (HA-MRSA), circulating strains of CA-MRSA have characteristic pathogenesis, strain characteristics, epidemiology, and clinical manifestations that are distinct from HA-MRSA. In fact, CA-MRSA probably behaves more like community-associated methicillin-sensitive S aureus (MSSA). This article reviews current knowledge of the epidemiology and clinical manifestations of community-associated S aureus and CA-MRSA infections.

Current knowledge of methicillin-resistant Staphylococcus aureus and community-associated methicillin-resistant Staphylococcus aureus

BACKGROUND

Bacterial strains that are oxacillin and methicillin-resistant, historically termed methicillin-resistant Staphylococcus aureus (MRSA) are resistant to all beta-lactam agents, including cephalosporins and carbapenems. MRSA are pathogenic and have a number of virulence factors that enable them to result in disease. They are transmissible and important causes of nosocomial infections worldwide. An MRSA outbreak can occur when one strain is transmitted to other patients or through close contacts of infected persons in the community. Hospital-associated MRSA (HA-MRSA) isolates are also frequent causes of healthcare-associated bloodstream and catheter-related infections. Community-associated MRSA (CA-MRSA) isolates are often only resistant to beta-lactam agents and erythromycin but they are an emerging cause of community-associated infections, especially skin and soft tissue infections (SSTI) and necrotizing pneumonia.

METHODS

Current possibilities for detecting MRSA strains in the laboratory are reviewed and discussed in the context of the recent literature.

RESULTS AND CONCLUSION

The active surveillance and prevention of MRSA occurrence and spreading in hospitals are discussed in the context of recent literature.

MRSA with progression from otitis media and sphenoid sinusitis to clival osteomyelitis, pachymeningitis and abducens nerve palsy in an immunocompetent 10-year-old patient

A previously healthy 10-year-old patient with headache, otalgia, and hearing loss was diagnosed with pachymeningitis and methicillin-resistant Staphylococcus aureus otitis media and bacteremia. Despite antimicrobial therapy, intracranial extension progressed, including clival osteomyelitis, sphenoid sinusitis, cavernous sinus inflammation and cranial nerve palsies, until the sphenoid sinus was drained. This case exemplifies an aggressive MRSA intracranial infection that advanced despite antibiotic therapy.

Coexistence of Panton-Valentine leukocidin-positive and -negative community-associated methicillin-resistant Staphylococcus aureus USA400 sibling strains in a large Canadian health-care region

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains often carry the Panton-Valentine leukocidin (PVL) genes. However, the specific role that PVL plays in the epidemiological features and pathogenesis of CA-MRSA infections has remained undefined and controversial. Conducting a retrospective study on a natural population of MRSA clinical isolates recovered from community and hospital patients in a large Canadian health-care region during a 6-year period, we identified the coexistence of 2 USA400 (a major clonal group of CA-MRSA) sibling strains with and without PVL genes. Polymerase chain reaction and sequence analysis indicated that the PVL-carrying prophage phiSa2mw was present in PVL(+) but absent in PVL(-) USA400 isolates. These strains shared identical genotypic and phenotypic properties and similar clinical characteristics. This study provides direct evidence that PVL genes are not necessarily the key determinants associated with the increasing dissemination of CA-MRSA strains, suggesting that the genomic milieu may play a greater role in this regard.

Antimicrobial-resistant pathogens: an emerging pediatric threat

The clinical impact of these three bacterial threats is readily apparent to any who practice pediatrics. The potential virulence of CA-MRSA and MDR pneumococci and the threat of failed antimicrobial options for MDRGN pose enormous challenges now and in the near future. With careful attention to antimicrobial stewardship, however, and knowledge of the clinical and epidemiologic factors of these organisms, one can hope to mitigate the impact on patient care and outcomes while awaiting ongoing discovery of new antimicrobial options. Most important, however, will be careful and thoughtful management of any new antimicrobial products to protect their efficacy for the future.