Cynthia Whitener

Vancomycin-Resistant Staphylococcus aureus in the Absence of Vancomycin Exposure

We report findings from our investigation of the worlds second clinical isolate of vancomycin-resistant Staphylococcus aureus (VRSA). An elderly man was hospitalized with an infected chronic heel ulcer and osteomyelitis. Before hospital admission, he received multiple courses of antibiotic therapy but, notably, no vancomycin. Numerous cultures of ulcer specimens (performed on an outpatient basis) grew methicillin-resistant, vancomycin-susceptible S. aureus and vancomycin-resistant Enterococcus species. At admission, an additional culture of a specimen from the heel ulcer grew S. aureus that was identified as VRSA (minimal inhibitory concentration for vancomycin [by broth-microdilution], 32 microg/mL). Further evaluation confirmed the presence of the vanA gene mediating vancomycin resistance. To assess VRSA transmission, we performed a carriage study of 283 identified contacts and an environmental survey of the patients home; no VRSA isolates were recovered. This case illustrates that recent exposure by patients to vancomycin is not necessary for development of vanA-containing VRSA. For clinical and public health reasons, it is essential that microbiology laboratories adequately test for vancomycin-resistance in S. aureus.

Characterization of a Daptomycin-Nonsusceptible Vancomycin-Intermediate Staphylococcus aureus Strain in a Patient with Endocarditis

ABSTRACT We analyzed the emergence of daptomycin nonsusceptibility in a patient with persistent vancomycin-intermediate Staphylococcus aureus (VISA) bacteremia. The daptomycin-nonsusceptible VISAs cell wall demonstrated a reduction in muramic acid O-acetylation, a phenotypic parameter not previously reported for VISA; some isolates also contained a single point mutation in the mprF gene.

Knee and hip arthroplasty infection rates in persons with haemophilia: a 27 year single center experience during the HIV epidemic

Summary.  Total joint replacement (TJR) is an option for the management of chronic haemophilic arthropathy. Because surgery is technically challenging, there is a high rate of deep prosthetic infections, particularly in human immunodeficiency virus (HIV)‐infected individuals. We determined the incidence of deep infection rates following total knee and hip arthroplasties in HIV‐seropositive and HIV‐seronegative persons with haemophilia. Fifty‐one primary joint replacements were performed on 32 patients seen at a regional comprehensive haemophilia care center from 1975 to 2002. Thirty prostheses were placed in patients who were HIV‐seropositive prior to surgery (n = 14) or seroconverted later (n = 16). Median age at the time of surgery was 33 years (range: 20–61) among 19 HIV‐seropositive patients and 35 years (range: 26–74) among 13 HIV‐negative patients. Median duration of follow‐up was 83 months (range: 2–323). Rate of primary joint infection per artificial joint‐year by HIV status was compared by Poisson regression. Main outcome measures were the incidence of primary replacement joint infections by HIV status. Deep infections developed in five (9.8%) of 51 replacement joints. There were two infections during 204.15 joint‐years without HIV infection and three infections during 205.28 joint‐years with HIV infection. The incidence rate of joint infection (0.98 vs. 1.46 per 100 joint‐years) was not increased with HIV (relative risk, RR: 1.49, 95% CI: 0.25–8.93, P = 0.66). We conclude that HIV infection is not a contraindication to knee or hip replacement arthroplasty in the appropriate clinical setting.

Risk of methicillin-resistant Staphylococcus aureus surgical site infection in patients with nasal MRSA colonization

BACKGROUND Patients colonized with methicillin-resistant Staphylococcus aureus (MRSA) are at increased risk for invasive infection compared with noncolonized patients; however, the magnitude of risk for MRSA surgical site infection (SSI) is unclear. To aid in planning of infection prevention strategies, we sought to assess the incidence of MRSA SSI in MRSA carriers. METHODS We conducted a retrospective cohort study at our tertiary care center of inpatients who underwent MRSA polymerase chain reaction (PCR) screen of the nares within 30 days before a National Healthcare Safety Network principal procedure between April 2008 and July 2010. RESULTS The rate of MRSA SSI was 1.86% in the MRSA PCR-positive group (n = 431) and 0.20% in the MRSA PCR-negative group (n = 9432). Multivariate analysis identified MRSA PCR-positive status as an independent risk factor for MRSA SSI (odds ratio, 9.20; 95% confidence interval, 3.81-20.47; P < .0001); other risk factors included duration of surgery ≥137 minutes, American Society of Anesthesiologists score ≥3, and abdominal surgery. CONCLUSIONS Surgical patients with a positive nasal MRSA PCR screen had a 9-fold greater odds of developing a subsequent MRSA SSI compared with patients with a negative nasal MRSA PCR screen. The incidence of MRSA SSI in PCR-positive patients was low (1.86%), however, and identifying subsets of patients at greatest risk for SSI may help target decolonization and other interventions.

Molecular and epidemiologic characteristics of linezolid-resistant coagulase-negative staphylococci at a tertiary care hospital.

We investigated emergence of linezolid resistance among coagulase-negative staphylococci at our tertiary care center in 2007. All 17 cases were healthcare associated, and prior administration of linezolid was documented <or=2 months before first isolation of linezolid-resistant coagulase-negative staphylococci for all but 1 patient. Pulse-field gel electrophoresis analysis of the 14 available strains demonstrated 1 predominant clonal type, suggesting nosocomial spread. In addition to mutations in 23S rRNA and L4 previously described, we observed novel alterations in the 23S rRNA gene (G(2215)A) and in the L3 protein (substitutions L(101)V, H(146)Q/R, F(147)I, V(154)L, M(156)T). The increase in linezolid-resistant coagulase-negative staphylococci correlated with nosocomial transmission of selected mutated strains in patients who had received linezolid.

Francisella novicida Bacteremia after a Near-Drowning Accident

ABSTRACT We describe a rare case of Francisella novicida bacteremia following a near-drowning event in seawater. We highlight the challenges associated with laboratory identification of F. novicida and differences in the epidemiology of F. novicida and Francisella tularensis infections.

Household risk factors for colonization with multidrug-resistant Staphylococcus aureus isolates.

Antimicrobial resistance, particularly in pathogens such as methicillin-resistant Staphylococcus aureus (MRSA), limits treatment options and increases healthcare costs. To understand patient risk factors, including household and animal contact, potentially associated with colonization with multidrug-resistant MRSA isolates, we performed a prospective study of case patients colonized with MRSA on admission to a rural tertiary care hospital. Patients were interviewed and antimicrobial resistance patterns were tested among isolates from admitted patients colonized with MRSA in 2009–10. Prevalence of resistance was compared by case-patient risk factors and length-of-stay outcome among 88 MRSA case patients. Results were compared to NHANES 2003–04. Overall prevalence of multidrug resistance (non-susceptibility to ≥four antimicrobial classes) in MRSA nasal isolates was high (73%) and was associated with a 1.5-day increase in subsequent length of stay (p = 0.008). History of hospitalization within the past six months, but not antimicrobial use in the same time period, was associated with resistance patterns. Within a subset of working-age case patients without recent history of hospitalization, animal contact was potentially associated with multidrug resistance. History of hospitalization, older age, and small household size were associated with multidrug resistance in NHANES data. In conclusion, recent hospitalization of case patients was predictive of antimicrobial resistance in MRSA isolates, but novel risk factors associated with the household may be emerging in CA-MRSA case patients. Understanding drivers of antimicrobial resistance in MRSA isolates is important to hospital infection control efforts, relevant to patient outcomes and to indicators of the economic burden of antimicrobial resistance.

Molecular and Phenotypic Characteristics of Healthcare- and Community-Associated Methicillin-Resistant Staphylococcus aureus at a Rural Hospital

Background While methicillin-resistant Staphylococcus aureus (MRSA) originally was associated with healthcare, distinct strains later emerged in patients with no prior hospital contact. The epidemiology of MRSA continues to evolve. Methods To characterize the current epidemiology of MRSA-colonized patients entering a hospital serving both rural and urban communities, we interviewed patients with MRSA-positive admission nasal swabs between August 2009 and March 2010. We applied hospitalization risk factor, antimicrobial resistance phenotype, and multi-locus sequence genotype (MLST) classification schemes to 94 case-patients. Results By MLST analysis, we identified 15 strains with two dominant clonal complexes (CCs)–CC5 (51 isolates), historically associated with hospitals, and CC8 (27 isolates), historically of community origin. Among patients with CC5 isolates, 43% reported no history of hospitalization within the past six months; for CC8, 67% reported the same. Classification by hospitalization risk factor did not correlate strongly with genotypic classification. Sensitivity of isolates to ciprofloxacin, clindamycin, or amikacin was associated with the CC8 genotype; however, among CC8 strains, 59% were resistant to ciprofloxacin, 15% to clindamycin, and 15% to amikacin. Conclusions Hospitalization history was not a strong surrogate for the CC5 genotype. Conversely, patients with a history of hospitalization were identified with the CC8 genotype. Although ciprofloxacin, clindamycin, and amikacin susceptibility distinguished CC8 strains, the high prevalence of ciprofloxacin resistance limited its predictive value. As CC8 strains become established in healthcare settings and CC5 strains disseminate into the community, community-associated MRSA definitions based on case-patient hospitalization history may prove less valuable in tracking community MRSA strains.

Clostridium difficile infection: a common clinical problem for the general internist

SummaryConsidering the current wide use of antimicrobial agents, the general internist is commonly faced with the patient at risk for diarrhea due toC. difficile. The diagnosis should be considered for any patient with diarrhea who has received any type of antibiotic therapy in the preceding 4–6 weeks. Symptoms may range from a minor bout of diarrhea to fulminant and fatal colitis. Diagnosis usually requires demonstration of the toxin in stool; culture of the organism and fiberoptic endoscopy may play an adjunctive role in selected clinical settings. The ultimate goal in the treatment forC. difficile infection is to repopulate the normal colonic flora in the most efficacious manner. Minimally symptomatic patients may respond to discontinuing the offending antimicrobial agent or using nonspecific binding agents. Oral vancomycin continues to be the “gold standard” for specific treatment, while metronidazole therapy is considered the first-line agent for individuals with milder infection. Oral bacitracin shows promise, though large studies are lacking. Patients with multiple relapses ofC. difficile diarrhea can be treated with prolonged courses of vancomycin or a combination of vancomycin and rifampin. Intensive care unit patients who are NPO have few therapeutic options besides intravenous administration of metronidazole and oral administration of vancomycin via clamped nasogastric tube. Preventive efforts are directed at cautious use of antibiotics and the use of vinyl gloves when caring for patients with known infection.

Improving Outcomes in Patients With Sepsis

Sepsis mortality may be improved by early recognition and appropriate treatment based on evidence-based guidelines. An intervention was developed that focused on earlier identification of sepsis, early antimicrobial administration, and an educational program that was disseminated throughout all hospital units and services. There were 1331 patients with sepsis during the intervention period and 1401 patients with sepsis during the control period. After controlling for expected mortality, patients in the intervention period had 30% lower odds of dying (odds ratio = 0.70, 95% confidence interval [CI] = 0.57 to 0.84). They also had 1.07 fewer days on average in the intensive care unit (95% CI = −1.98 to −0.16), 2.15 fewer hospital days (95% CI = −3.45 to −0.86), and incurred on average