Post on 25-May-2015
NOSOCOMIAL INFECTIONS
ETIOLOGY & DIAGNOSIS
ETIOLOGY
The causative agents of nosocomial infections incude
• Bacteria• Viruses• Fungi
BACTERIA
• Gram-negative bacteria (Pseudomonas aeruginosa, Aeromonas hydrophilia, Burkholderia cepacia, Stenotrophomonas maltophilia, Serratia marcescens, Flavobacterium meningosepticum, Acinetobacter calcoaceticus, and Legionella pneumophila)
• Mycobacteria (Mycobacterium xenopi, Mycobacterium chelonae, or Mycobacterium avium-intracellularae)
• Gram positive cocci• Salmonella species• Staphylococcus aureus• Clostridium perfringens• Clostridium botulinum• Bacilluscereus • Escherichia coli• Campylobacter jejuni
• Yersinia enterocolitica• Vibrio parahaemolyticus• Vibrio cholerae• Aeromonas hydrophilia• Streptococcus species• Listeria monocytogenes
VIRUSES
• Varicella zoster (chickenpox)• Influenza• Molluscum contagiosum• Human papillomavirus • Noroviruses• RotavirusCaliciviruses
FUNGI
• Aspergillus• Exophiala jeanselmei
DIAGNOSIS
• UTI• Bacteremia• Pneumonia• Surgical wounds
BACTEREMIA
SPECIMEN COLLECTION• Venipuncture• The skin is cleaned with 80% to 90% ethanol
followed by an iodine based compound scrubbed in a concentric fashion qround the venipuncture site
BLOOD CULTURE METHODS• Aerobic culture bottle • It contains a soybean casein digest broth,
trypticase soy broth,brain heart infusion ,brucella agar, or columbia broth base
• Anaerobic broth media contain same contents but 0.5% cysteine may be added
ANTICOAGULANTS AND OTHER ADDITIVES:• Sodium polyanetholsulfonaye• Sodium amylosulfate• Sodium citrate• EDTA
NEWER BLOOD CULTURE SYSTEMS
BIPHASIC BROTH-SLIDE SYSTEM: consists of a slide paddle containing chocolate, macconkey, and malt extract agars in a standard broth bottle. Bacterial growth appears as small discrete colonies or confluent growth on he paddle
CONTINUOS MONITORING BLOOD CULTURE SYSTEMS:
• BACTEC system involves measuring the amount of 14CO2 released from the bacterial colonies and calculating the growth index
PNEUMONIA
SPECIMEN COLLECTION:• Patients should be instructed to rinse out their
mouth and collect a deep sputum specimen• The purpose is to collect lung secretions and
not saliva or drainage from nasopharynx• Bronchoscope may also be used
DIRECT MICROSCOPIC EXAMINATION:• Direct gram stained smear• Samples with greater than 25 neutrophils and
fewer than 10 epithelial cells are positive• The morphology of the organisms present also
helpsCULTURE:• Sheeps blood agar, macconkey, and chocolate
agar plates are used for culture
CHRONIC PNEUMONIA
DIRECT MICROSCOPY:• Acid fast stains such as Kinyoun, Ziehl Neelson
are used for mycobacterium• Potassium hydroxide and coflour white are
commonly used to detect yeast cells and hyphal elements
• Culture and rapid diagnostic tests such as Nucleic amplification test are also used
SURGICAL INFECTIONS
• Specimen is collected by wound swabs , drainage collection and tissue sample
• Culture methods are used for culturing the tissue sample
• Examination is done by histopathologic or radiographic examination
UTI
SPECIMEN COLLECTION: Cntamination by vaginal, anal and urethral flora
should be preventedMIDSTREAM SPECIMEN COLLECTION:• The first portion of the voided urine is discarded
and the midstream urine is collected• This is done to prevent the contamination by
normal flora
CATHETERISED SPECIMEN COLLECTION:• Invasive technique reduces the risk of
contamination by normal flora• Unclean catheter may lead to infection and
contaminationSUPRAPUBIC ASPIRATION:• With the bladder full, the urine is collected
with a needle and syringe followed by skin antisepsis
• Done usually in infants
SCREENS PRINCIPLE THRESHOLD OF DETECTION
ManualMicroscopy Direct,uncentrifuged or centrifuged
Recognition of organism morphotypes and gram stain
>1 organism per OIF = >105
ChemicalEnzymatic dipstick Nitrate reductase WBC esterase Chemstrip LNEnzyme tube UriscreenCalorimetric particle filtration
Gram –ve bacteria reduce nitratesPresence of WBC enzymes
Measures catalase
Membrane filtration and detection
>105
5 WBC per field>10 to 10
>104 to 105
>104
AUTOMATED PRINCIPLE THRESHOLDBioluminescence UTI screen
Detected bacterial ATP
>104 to 105
Photometry If a significant amount are present in the specimen, they will grow in the medium
> 104 to 105
Calorimetric particle filtration
Membrane filtration and detection by safranin O dye
> 104 to 105