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