Methicillin-Resistant Staphylococcus aureus (MRSA): focus on Community-Associated MRSA

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are defined as occurring in patients who have no association with the healthcare setting. CA-MRSA has emerged as a common cause of community infections in the US and are distinct from MRSA strains classically associated with healthcare-associated infections from genotypic and phenotypic perspectives. They are frequently susceptible to non-beta-lactam antimicrobials; express the SCCmec type IV or V gene and contain the Panton-Valentine leukocidin virulence factor. They most commonly cause mild skin infections; but have been associated with severe soft tissue infection and with necrotising pneumonia

Clinical implications and treatment of multiresistant Streptococcus pneumoniae pneumonia.

Streptococcus pneumoniae is the leading bacterial cause of community-acquired respiratory tract infections. Prior to the 1970s this pathogen was uniformly susceptible to penicillin and most other antimicrobials. However, since the 1990s there has been a significant increase in drug-resistant Streptococcus pneumoniae (DRSP) due, in large part, to increased use of antimicrobials. The clinical significance of this resistance is not definitely established, but appears to be most relevant to specific MICs for specific antimicrobials. Certain beta-lactams (amoxicillin, cefotaxime, ceftriaxone), the respiratory fluoroquinolones, and telithromycin are among several agents that remain effective against DRSP. Continued surveillance studies, appropriate antimicrobial usage campaigns, stratification of patients based on known risk factors for resistance, and vaccination programmes are needed to appropriately manage DRSP and limit its spread.

Double-blind, randomized study of the efficacy and safety of oral pharmacokinetically enhanced amoxicillin-clavulanate (2,000/125 milligrams) versus those of amoxicillin-clavulanate (875/125 milligrams), both given twice daily for 7 days, in treatment of bacterial community-acquired pneumonia in adults.

This randomized, double-blind, noninferiority trial was designed to demonstrate that pharmacokinetically enhanced amoxicillin-clavulanate (2,000/125 mg) was at least as effective clinically as amoxicillin-clavulanate 875/125 mg, both given twice daily for 7 days, in the treatment of community-acquired pneumonia in adults. In total, 633 clinically and radiologically confirmed community-acquired pneumonia patients (intent-to-treat population) were randomized to receive either oral amoxicillin-clavulanate 2,000/125 mg (n = 322) or oral amoxicillin-clavulanate 875/125 mg (n = 311). At screening, 160 of 633 (25.3%) patients had at least one typical pathogen isolated from expectorated or invasive sputum samples or blood culture (bacteriology intent-to-treat population). Streptococcus pneumoniae (58 of 160, 36.3%), methicillin-susceptible Staphylococcus aureus (34 of 160, 21.3%), and Haemophilus influenzae (33 of 160, 20.6%) were the most common typical causative pathogens isolated in both groups in the bacteriology intent-to-treat population. Clinical success in the clinical per protocol population at test of cure (days 16 to 37), the primary efficacy endpoint, was 90.3% (223 of 247) for amoxicillin-clavulanate 2,000/125 mg and 87.6% (198 of 226) for amoxicillin-clavulanate 875/125 mg (treatment difference, 2.7; 95% confidence interval, -3.0, 8.3). Bacteriological success at test of cure in the bacteriology per protocol population was 86.6% (58 of 67) for amoxicillin-clavulanate 2,000/125 mg and 78.4% (40 of 51) for amoxicillin-clavulanate 875/125 mg (treatment difference, 8.1%; 95% confidence interval, -5.8, 22.1). Both therapies were well tolerated. Amoxicillin-clavulanate 2,000/125 mg twice daily was shown to be as clinically effective as amoxicillin-clavulanate 875/125 mg twice daily for 7 days in the treatment of adult patients with community-acquired pneumonia, without a noted increase in the reported rate of adverse events.

Optimal treatment strategies for community-acquired pneumonia: non-responders to conventional regimens.

When patients with community-acquired pneumonia (CAP) fail to respond after initiation of empirical therapy, it is necessary for the physician to consider a number of possibilities. The diagnosis should be reviewed, with consideration given to both non-infectious and infectious illnesses. If the diagnosis is correct, the failure may relate to three areas: host-related problems, including overwhelming infection and empyema, pathogen-related problems, including infection caused by an unusual or resistant pathogen, and drug-related problems, including inappropriate dose of drug, poor compliance, malabsorption, and drug interactions. A systematic therapeutic approach including a microbiological evaluation to identify the causative pathogen and its susceptibility will help to ensure that an appropriate antimicrobial agent is used.

Efficacy and safety of gemifloxacin in the treatment of community-acquired pneumonia: a randomized, double-blind comparison with trovafloxacin.

This multicentre, randomized, double blind, parallel group study compared the efficacy and safety of gemifloxacin (320 mg once daily) with trovafloxacin (200 mg once daily) in 571 patients with community-acquired pneumonia (CAP). Although treatment was given routinely for 7 days it could be extended to 14 days; two-thirds of patients were treated for 7 days. High clinical success rates were noted at follow-up in the per-protocol population in both the gemifloxacin group (95.8%) and the trovafloxacin group (93.6%), non-inferiority with 95% CI. In the intent-to-treat population, the clinical success rate at follow-up was significantly superior for gemifloxacin (87.6%) compared with trovafloxacin (81.1%; 95% CI 0.5, 12.4). The pathogens identified most commonly at presentation were Mycoplasma pneumoniae and Streptococcus pneumoniae. Gemifloxacin eradicated 100% of S. pneumoniae. One bacteraemic isolate of S. pneumoniae was associated with clinical failure in the trovafloxacin group (MIC of trovafloxacin 8 mg/L). Gemifloxacin was well tolerated and the incidence of transient liver function abnormalities was very low. Gemifloxacin is an effective and well-tolerated treatment for patients with CAP.

Efficacy and safety of gemifloxacin 320 mg once-daily for 7 days in the treatment of adult lower respiratory tract infections.

An open-label, non-comparative study assessed the clinical and bacteriological efficacy of gemifloxacin (320 mg, once-daily for 7 days) in lower respiratory tract infections (LRTI). Patients with acute exacerbation of chronic bronchitis (AECB, n=261) or community-acquired pneumonia (CAP, n=216) were enrolled into the study. Clinical success rates at follow-up (days 21-28) in the intent-to-treat (ITT) population were high, 83.1% in AECB patients (95% CI: 77.9, 87.4) and 82.9% in CAP patients (95% CI: 77.0, 87.5). High bacteriological success rates were achieved (bacteriological ITT population), 91.2% (52/57) in AECB patients (95% CI: 80.0, 96.7) and 77.9% (60/77) in CAP patients (95% CI: 66.8, 86.3). Gemifloxacin was well tolerated with a low incidence of adverse events. Gemifloxacin treatment resulted in high clinical and bacteriological success rates and is a well-tolerated therapy for the treatment of LRTIs.

The epidemiology of respiratory tract infections.

Respiratory tract infections (RTIs) are the most common, and potentially most severe, of infections treated by health care practitioners. Lower RTIs along with influenza, are the most common cause of death by infection in the United States. Risk factors for pneumonia and other respiratory tract infections include: extremes of age (very young and elderly), smoking, alcoholism, immunosuppression, and comorbid conditions. The microbial cause of RTIs vary depending on the infection (i.e., pneumonia compared with acute bacterial sinusitis), setting (i.e., community-acquired compared with nosocomial), and other factors. The causative pathogens associated with CAP have changed in prevalence over time. Although Streptococcus pneumoniae remains the most common causative pathogen, a number of newer pathogens, such as Chlamydia pneumoniae and sin nombre virus, have been recognized in recent years. The emerging antimicrobial resistance of respiratory pathogens (most notably S. pneumoniae) has also increased the challenge for appropriate management of RTI. An awareness of the epidemiology and cause of specific respiratory infections should optimize care.

Azithromycin vs cefuroxime plus erythromycin for empirical treatment of community-acquired pneumonia in hospitalized patients: a prospective, randomized, multicenter trial.

OBJECTIVE: To compare the efficacy and safety of azithromycin dihydrate monotherapy with those of a combination of cefuroxime axetil plus erythromycin as empirical therapy for community-acquired pneumonia in hospitalized patients. METHODS: Patients were enrolled in a prospective, randomized, multicenter study. The standard therapy of cefuroxime plus erythromycin was consistent with the American Thoracic Society, Canadian Community-Acquired Pneumonia Consensus Group, and Infectious Disease Society of America consensus guidelines. The doses were intravenous azithromycin (500 mg once daily) followed by oral azithromycin (500 mg once daily), intravenous cefuroxime (750 mg every 8 hours), followed by oral cefuroxime axetil (500 mg twice daily), and erythromycin (500-1000 mg) intravenously or orally every 6 hours. Randomization was stratified by severity of illness and age. Patients who were immunosuppressed or residing in nursing homes were excluded. RESULTS: Data from 145 patients (67 received azithromycin and 78 received cefuroxime plus erythromycin) were evaluable. Streptococcus pneumoniae and Haemophilus influenzae were isolated in 19% (28/145) and 13% (19/145), respectively. The atypical pathogens accounted for 33% (48/145) of the etiologic diagnoses; Legionella pneumophila, Chlamydia pneumoniae, and Mycoplasma pneumoniae were identified in 14% (20/ 145), 10% (15/145), and 9% (13/145), respectively. Clinical cure was achieved in 91% (61/67) of the patients in the azithromycin group and 91% (71/78) in the cefuroxime plus erythromycin group. Adverse events (intravenous catheter site reactions, gastrointestinal tract disturbances) were significantly more common in patients who received cefuroxime plus erythromycin (49% [30/78]) than in patients who received azithromycin (12% [8/67]) (P<.001). CONCLUSIONS: Treatment with azithromycin was as effective as cefuroxime plus erythromycin in the empirical management of community-acquired pneumonia in immunocompetent patients who were hospitalized. Azithromycin was well tolerated.

Group A streptococcus necrotizing fasciitis.

Necrotizing fasciitis due to Group A streptococcus has been observed with increasing frequency over the past decade. Appropriate management requires rapid recognition of this life-threatening infection and expeditious antimicrobial therapy as well as surgical debridement or excision of tissue.

The radiologic manifestations of Legionnaire's disease. The Ohio Community-Based Pneumonia Incidence Study Group.

STUDY OBJECTIVES: To study the serial radiographic manifestations of Legionnaire's disease from the initial presentation on admission to recovery using strict criteria for the diagnosis of infection. MATERIALS AND METHODS: We prospectively studied the chest radiographs of patients hospitalized with a diagnosis of community-acquired pneumonia in Summit County, Ohio between November 1990 and November 1992. Forty-three patients fulfilled strict criteria for legionellosis. The diagnosis of infection was based on the criteria of "definite" diagnosis as defined by the Ohio Community-Based Pneumonia Incidence Study Group report. The criteria included the isolation of the microorganism, the presence of a significant antibody rise, or the presence of Legionella antigen in the urine. RESULTS: Forty of 43 patients had admission radiographs interpreted as compatible with pneumonia. In spite of appropriate antimicrobial therapy, worsening of the infiltrates was found in more than half of the patients within the first week. Twenty-seven patients were observed to have pleural effusion during the course of hospitalization: 10 effusions were found on admission, another 14 developed during the first week, and 3 new effusions were discovered after the first week. Cavitation was found in only one patient. None of the patients had apical involvement. CONCLUSION: This study confirms previous reports using less stringent etiologic diagnosis criteria that chest radiographic findings in Legionnaire's disease are not specific. Even with appropriate therapy, more than half of the patients will have worsening of the infiltrates during the first week. Pleural effusion is common among our patients, and it is frequently detected during the serial radiographic studies during the first week of hospitalization. Chest radiography in Legionnaire's disease is useful only for the monitoring of disease progression and not for diagnostic purposes. In addition, worsening of infiltrates and pleural effusion are seen in more than half of the patients in spite of appropriate therapy and clinical improvement.

Chlamydia pneumoniae pneumonia.

Chlamydia pneumoniae is a common cause of community-acquired pneumonia. At present there is no "gold'' standard for diagnosis and there is no easily accessible means of rapid diagnosis available. The best indication of acute C. pneumoniae infection is a fourfold rise in antibody titer, accompanying a positive polymerase chain reaction or culture. C. pneumoniae is usually associated with nonsevere clinical manifestations but the features will vary depending upon the occurrence as primary or reinfection syndrome, the presence of co-pathogens, or the existence of co-morbid conditions. C. pneumoniae has been described as a cause of severe disease requiring intensive care unit admission. Recommendations for therapy of C. pneumoniae pneumonia include macrolides, tetracyclines, or the new fluoroquinolones.

Clinical characteristics of Chlamydia pneumoniae infection as the sole cause of community-acquired pneumonia.

The clinical characteristics of 26 patients with community-acquired pneumonia due to Chlamydia pneumoniae as the only identified pathogen who required hospitalization were evaluated. Most patients (18) had reinfection based on serological results. The mean age of the patients was 55 years (38 years, patients with primary infection; 63 years, patients with reinfection), and the gender representation was equal. Generally, illness was mild and associated with limited temperature elevation and nonspecific symptoms. The presence of comorbid illnesses and the requirement of supplemental oxygen therapy were the most common criteria for hospital admission.

Parainfluenza virus infection among adults hospitalized for lower respiratory tract infection.

To better define the contribution of human parainfluenza viruses (HPIVs) to lower respiratory tract infection in adults, we tested acute- and convalescent-phase serum specimens from hospitalized adults participating in a population-based prospective study of lower respiratory tract infection during 1991-1992. We tested all available specimens from the epidemic seasons for each virus and approximately 300 randomly selected specimens from the corresponding off-seasons for antibodies to HPIV-1, HPIV-2, or HPIV-3. During the respective epidemic season, HPIV-1 infection was detected in 18 (2.5%) of 721 and HPIV-3 infection in 22 (3.1%) of 705 patients with lower respiratory tract infection. Only 2 (0.2%) of 1,057 patients tested positive for HPIV-2 infection. No HPIV-1 infections and only 2 (0.7% of 281 patients tested) HPIV-3 infections were detected during the off-seasons. HPIV-1 and HPIV-3 were among the four most frequently identified infections associated with lower respiratory tract infection during their respective outbreak seasons.

Levofloxacin in the treatment of community acquired pneumonia.

Levofloxacin is the first fluoroquinolone with enhanced activity against Streptococcus pneumoniae to be released in Canada. In vitro, it is active against more than 99% of isolates of S pneumoniae, even those resistant to penicillin. It is also active against respiratory pathogens such as Haemophilus influenzae, Moraxella catarrhalis, Mycoplasma pneumoniae, Chlamydia pneumoniae and Legionella species. When given orally, bioavailability is greater than 99%, and the drug is highly concentrated in lung tissue and macrophages. Drug levels are compatible with once-daily dosing. In a large clinical trial, levofloxacin has shown clinical and microbiological superiority compared with ceftriaxone/cefuroxime. The characteristics of levofloxacin - high oral bioavailability, long duration of effect, activity against key respiratory pathogens and high tolerability - suggest that it will be a useful drug in the treatment of community acquired pneumonia.

Overview of resistance in the 1990s.

The tremendous therapeutic advantage afforded by antibiotics is being threatened by the emergence of increasingly resistant strains of microbes. Selective pressure favoring resistant strains arises from misuse and overuse of antimicrobials (notably extended-spectrum cephalosporins), increased numbers of immunocompromised hosts, lapses in infection control, increased use of invasive procedures and devices, and the widespread use of antibiotics in agriculture and animal husbandry. Outside the hospital, penicillin-resistant Streptococcus pneumoniae is of greatest concern; recent reports also indicate the appearance of outpatient methicillin-resistant Staphylococcus aureus (MRSA) infections. MRSA is a significant problem in the hospital, as are vancomycin-resistant Enterococcus, oxacillin-resistant S aureus, and multidrug-resistant Gram-negative bacilli. Owing to the high rate of antibiotic use and other risk factors, a person is more likely to acquire an antibiotic-resistant infection in the ICU than anywhere else, either inside or outside the hospital. Responsible antibiotic use and stringent infection-control policies are needed to discourage the development of resistant strains.

Accuracy of ICD-9-CM codes in detecting community-acquired pneumococcal pneumonia for incidence and vaccine efficacy studies.

Studies have used medical record discharge data as coded by the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) to estimate pneumococcal pneumonia incidence and vaccine efficacy. However, the accuracy of coding data to identify laboratory-confirmed pneumococcal pneumonia is not known. With the use of information collected in Ohio for a community-based pneumonia incidence study, the authors calculated the sensitivities, specificities, positive predictive values (PPV), and negative predictive values (NPV) of specific codes for pneumococcal pneumonia among hospitalized patients with community-acquired pneumonia. Sensitivities of the most common ICD-9-CM codes listed in the first five positions for patients with laboratory-confirmed pneumococcal pneumonia were 58.3% (code 481.0, pneumococcal pneumonia), 20.4% (38.0, streptococcal septicemia), 19.2% (38.2, pneumococcal septicemia), 15.0% (518.81, respiratory failure), 14.2% (486.0, pneumonia, organism unspecified), and 11.3% (482.3, streptococcal pneumonia). Using the first five listed ICD-9-CM codes rather than just the first listed code increased sensitivity without causing substantial change in specificity, PPV, and NPV. Sensitivity, PPV, and NPV of individual and groups of codes varied with different case definitions of pneumococcal pneumonia. Incidence and vaccine efficacy studies with the ability to validate diagnoses by medical chart review can use a combination of many ICD-9-CM codes to maximize sensitivity. However, without the ability to review medical charts, researchers must carefully decide which codes would best suit their studies.

Cryptococcal meningitis in renal transplant patients associated with environmental exposure.

Fungal infections in renal transplant recipients are less common than bacterial infections; however, the morbidity from fungal infections is high. There is limited information in the literature concerning post-transplantation cryptococcal infection due to environmental exposure of patients living in high-risk areas. We report three patients who were diagnosed with cryptococcal meningitis after kidney transplantation. Cryptococcal titers prior to transplant surgery were negative in all three patients. These patients all lived in rural areas and demonstrated evidence of environmental exposure leading to subsequent cryptococcal meningitis. All patients had exposure to pigeon and chicken excreta and, after treatment, two patients are alive and well with excellent allograft function. The third patient has marginal renal function but is currently not on dialysis. Early diagnosis is essential for salvage from these potentially lethal infections. Intense headache was a prominent feature in the clinical presentation of our patients, and should signal the need for early sampling and culture of spinal fluid. Meningismus was not present in any of our patients, even when other systemic symptoms were identified. We recommend a high index of suspicion post-transplantation for all patients who may have environmental or occupational exposure to cryptococcus. If infection is detected quickly and treatment instituted promptly, patient recovery and allograft survival are possible. Long-term therapy with fluconazole, a non-nephrotoxic agent, should permit eradication of the infection with preservation of kidney function.

Diagnosis and treatment of diabetic foot infections.

Prompt clinical diagnosis and timely treatment are the hallmarks of the proper care of diabetic patients with foot infections. The importance of careful clinical foot examination cannot be overemphasized. When infection is suspected, effort should be made to search for deeper infections, especially osteomyelitis. Numerous imaging techniques are available, but their cost-effectiveness has not been fully determined. Radiography of the foot is less sensitive but can provide useful information at a lower cost. Radio-isotope studies have not yielded consistent results, but the newer techniques deserve attention. Microbiological diagnosis should be attempted using only deep tissue culture, including bone biopsy. The primary aim of treatment of the infected foot is to restore ambulation. Timely surgical intervention and appropriate antimicrobial therapy can reduce the incidence of above-ankle amputation and reduce the length of hospital stay.