Nosocomial Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Nosocomial and links to relevant pages within the course.
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Podschun R. Ullmann U.: Klebsiella spp. as nosocomial pathogens: epidemiology, taxonomy, typing methods, and pathogenicity factors Clinical Microbiology Reviews. 11(4):589-603, 1998 Bacteria belonging to the genus Klebsiella frequently cause human nosocomial infections. In particular, the medically most important Klebsiella species, Klebsiella pneumoniae, accounts for a significant proportion of hospital-acquired urinary tract infections, pneumonia, septicemias, and soft tissue infections. The principal pathogenic reservoirs for transmission of Klebsiella are the gastrointestinal tract and the hands of hospital personnel. Because of their ability to spread rapidly in the hospital environment, these bacteria tend to cause nosocomial outbreaks. Hospital outbreaks of multidrug-resistant Klebsiella species, especially those in neonatal wards, are often caused by new types of strains, the so-called extended-spectrum-beta-lactamase (ESBL) producers The incidence of ESBL-producing strains among clinical Klebsiella isolates has been steadily increasing over the past years. The resulting limitations on the therapeutic options demand new measures for the management of Klebsiella hospital infections. While the different typing methods are useful epidemiological tools for infection control, recent findings about Klebsiella virulence factors have provided new insights into the pathogenic strategies of these bacteria. Klebsiella pathogenicity factors such as capsules or lipopolysaccharides are presently considered to be promising candidates for vaccination efforts that may serve as immunological infection control measures.
Hershow RC. Khayr WF. Smith NL.: A comparison of clinical virulence of nosocomially acquired methicillin-resistant and methicillin-sensitive Staphylococcus aureus infections in a university hospital (University of Illinois at Chicago). Infection Control & Hospital Epidemiology. 13(10):587-93, 1992 OBJECTIVES: To compare the clinical virulence of nosocomially acquired methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) infections in 1989. DESIGN: A retrospective comparison of host factors, in-hospital exposures, sites of infections, and outcomes of patients with nosocomial MRSA and MSSA infections. PARTICIPANTS: Forty-four adult patients with nosocomial S.aureus infections. RESULTS: The 22 MRSA-infected and 22 MSSA-infected persons were similar regarding mean age, gender, underlying diseases, and exposure to surgery. Before developing infection, MRSA-infected persons were more likely to have received antibiotics and to have stayed in the hospital > 2 weeks. Bacteremia was the most common presentation in the MRSA and MSSA groups (55% and 59%, respectively). Infectious complications and death were infrequent in both groups. CONCLUSIONS: MRSA and MSSA strains infect patients with similar demographic features and underlying diseases, but MRSA infections are significantly more common among patients with previous antibiotic therapy and a prolonged preinfection hospital stay. Clinical presentations and outcomes did not differ significantly between the 2 groups. Thus, similar to studies in the early 1980s, our findings do not suggest greater intrinsic virulence of MRSA.
|Healthcare (Hospital)-Associated MRSA versus Community-Associated MRSA|
As mentioned in the course introduction, MRSA infections fall into two general types:Healthcare-associated MRSA (HA-MRSA) Infections that occur in people who are, or have recently been, hospitalized. Community-acquired MRSA (CA-MRSA) Infections that are apparently acquired in the community There are a number of factors that distinguish HA-MRSA from CA-MRSA isolates. These factors are summarized in the table below.FactorHA-MRSA CA-MRSAOrigin of strainsNosocomial infectionsFive isolates associated with healthcare settings: USA100, -200, -500, -600, -800USA100 is the predominant isolate while USA 200 is the second most common isolate. USA700 has been isolated in both healthcare and community settings.Evolved from endemic methicillin-susceptible S. aureus (MSSA) strains Two clones, USA300 and USA400, are associated with the majority of CA-MRSA infections in the United States. USA300 has emerged as the most prominent clone and is not found among hospital strains.Genetic lineageIsolates usually carry large SCCmec types I, II or III (34-67 kb)The larger size of SCCmecII and III permits the inclusion of other non-beta-lactam resistance genes so that HA-MRSA strains tend to be multi-drug resistantIsolates carry a smaller SCCmec variant, predominantly type IV (24 kb), less often type V or variant VT. SCCmecIV (except for mecA) does not permit the inclusion of other non-beta lactam resistance genes so that CA-MRSA isolates exhibit resistance to only methicillin and erythromycin and are more often susceptible to other non-beta lactam antibiotics (eg., trimethoprim/sulfamethoxazole (SXT) and clindamycin). Affected populationLargely affects older adults and people with weakened immune systems; those who have undergone surgical procedures are at increased risk. Healthy persons in the general population without established risk factors for MRSA acquisitionClinical syndromesFound at multiple sites, most commonly bloodstream infections, urinary tract infections (UTI) and respiratory tract infectionsPredominantly skin and soft tissue infections (SSTIs), such as abscesses, cellulitis, folliculitis and impetigo and a serious form of pneumoniaGenes for Panton-Valentine leukocidin (PVL) are associated with SCCmecIV; the clinical spectrum of infections caused by CA-MRSA is directly related to the presence of PVL genes, coding for the production of a cytotoxin that causes tissue necrosis and leukocyte destruction.
Stool culture is very effective in detecting C. difficile. Unfortunately, non-toxigenic strains will also grow, requiring strains to be tested for toxin production. The greatest disadvantage to culture is the length of time that is needed before results are available, which may be up to four days. However, antibiotic sensitivity testing following culture is useful for strain-typing that would provide necessary epidemiological information during nosocomial outbreaks.Colonies of C. difficile will appear white, flat, and spreading on blood agar (see top image on the right). Cycloserin-cefoxitin-fructose agar(CCFA) is a selective media that is used for isolation of C. difficile. There is however, no distinction between pathogenic and commensal strains, which all produce yellow colonies with a characteristic "ground glass" appearance. as shown in the bottom image on the right. The characteristic odor of "horse manure" aids in identification of C. difficile. Stool samples are directly inoculated onto CCFA and incubated in an anaerobic atmosphere at 37°C for 48 hours. Large, thin, gram-positive bacilli with spores will be observed on a Gram stain of a typical colony, as shown below.
|The colonies illustrated in this photograph were recovered from a blood culture after 48 hour incubation at 30°C. The most likely source for the septicemia is:||View Page|