28 December 2009

Clinically Relevant Microbiology Starts at the Source



Clinically Relevant Microbiology Starts at the Source
By: Mike Costello, PhD, MT(ASCP)
ACL Laboratories
Mary Dikeman, MT (ASCP)
Affinity Health System

Program Objectives
* Emphasize that obtaining sensitive and specific microbiology results begins with the patient and not at the door of the microbiology laboratory.
* Accentuate the importance of proper collection and transport of specimens in both local and referral environments
* Stress the importance of timely communication between the Microbiology laboratory and those collecting specimens
* Describe common pitfalls in specimen collection and transport
* Discuss What rules or principles must be followed in order to collect microbiology specimens which will accurately reflect the pathogenesis of the microbiological agent. (Church D. The Seven Principles of Accurate Microbiology Specimen Collection. . Calgary Laboratory Services Microbiology Newsletter. Volume 6, 2005)

Introduction
The practice of sensitive, specific and cost effective clinical microbiology is intimately tied to the submission and proper handling of optimal specimens for analysis. Unfortunately, these aspects of clinical microbiology are not as critically controlled as our laboratory assays. It is our responsibility to educate and notify our healthcare colleagues when specimens arrive at the laboratory that will yield inferior results.

Quality assurance of specimen collection and transport is a never ending battle and requires long term commitment of your time and resources, but the end results are better patient care and a more rewarding experience for those of us who work in the microbiology laboratory.

Principle #1: The specimen must be collected with a minimum of contamination as close to
site of infection as possible

Urine Culture Contamination Rates

* Urine Culture contamination rates (>2 bacteria at >100,000 CFU) should be <20%
o CAP Q-Probe study (Valenstein P Meier F. Urine culture contamination: a College of American Pathologists Q-Probes study of contaminated urine cultures in 906 institutions. Arch Pathol Lab Med. 1998;122:123-129)..
+ 630 participants collected information of 155,037 urine culture specimens; 20.1% were considered contaminated (>2 organisms at >105 CFU)
+ The top 10% of institutions reported a rate of 5.6%. Bottom 10% of institutions reported a contamination rate of 36.8%
+ Males have a lower contamination rate than females (11.2% Vs. 22.8%)
+ ER departments had a contamination rate of 17.8%, sites adjacent to lab had rates of 19.5%, and other sites had rates of 22.1%

Blood Culture
* Two sets of blood cultures should be drawn. Number of sets positive correlates with true sepsis (except for coagulase negative Staph?) (Clin Microbiol. Rev 19:788-802, 2006)
* Catheter drawn blood cultures
o Catheter drawn blood cultures are equally likely to be truly positive (associated with sepsis), but more likely to be colonized (J Clin Microbiol 38:3393, 2001.)
+ One drawn through catheter and other though vein PPV 0f 96%
+ Both drawn from catheter PPV 0f 50%
+ Both drawn through vein PPV of 98%
o Study of positive coagulase negative Staphylococcus cultures and sepsis (Clin Infect Dis. 39:333, 2004.)

Blood Culture Contamination Rate
By Service Drawing Culture
What is an “Acceptable” Blood Culture Contamination Rate for Your Lab??
Blood Culture Contamination in Pediatric Patients
Young Children and Young Doctors
Inexperienced physician-young child
Inexperienced physician-older child
Experienced physician-younger child
Experienced physician-older child
Predicative Value of a Positive Result
False Positive
True Positive
Variable
Ped Infect Dis. 2006, 25:611-614.

Inexperienced Physicians = Interns and residents in 1st half of training
Experience Physicians = Residents in 2nd half of training and senior physicians
What is an “Acceptable” Blood Culture Contamination Rate for Your Lab??

What is an “acceptable” blood culture contamination rate*?
Berkeris LG, JA Toworek, MK Walsh, PN Valenstein. Trends in Blood Culture Contamination.
Arch Pathol Lab Med 129:1222-1294, 2005

Respiratory Cultures

Read more...

Specimen Collection and Laboratory Diagnosis of Lower Respiratory Infections



Specimen Collection and Laboratory Diagnosis of Lower Respiratory Infections

By:Mohammad Rahbar (PhD)
Department Of Microbiology Reference Laboratory of Iran

Anatomy of Respiratory Tract

“ The culture of lower respiratory specimens may result in more unnecessary microbiologic effort than any other type of specimen.”
Raymond C Bartlett

Lower Respiratory Tract Infections
Epidemiology
* Pneumonia is the sixth leading cause of death in US
* Increasing numbers of patients at risk
o Aging population
o Increase in patients with immunocompromising conditions
* Overtreatment has lead to resistance
o Multidrug resistant Streptococcus pneumoniae
o Resistance among hospital acquired pathogens such as Acinetobacter, Pseudomonas aeruginosa E.coli K.pneumonia (ESBLs) MRSA and others
* Major sections
o Clinical aspects of diseases of LRT
o Specimen collection
o Specimen processing
o Interpretation of bacterial cultures
o Most common pathogens
o Methods for implementing change
o Guidelines for frequency of testing
o Public health issues
o Reimbursement codes

Categories of Lower Respiratory Tract Infections
* Acute bronchitis
* Community acquired pneumonia
* Hospital acquired pneumonia
* Pneumonia in the immunocompromised host

Community Acquired Pneumonia Etiologic Agents
Community Acquired Pneumonia Diagnosis

Available Test Methodologies
* Sputum Gram stain and culture
* Blood cultures
* Serologic studies
* Antigen detection tests
* Nucleic acid amplification tests

Sputum Gram Stain and Culture
Proponents
* Demonstration of predominant morphotype on Gram stain guides therapy
* Accuracy is good when strict criteria are used
* Cheap, so why not?

Antagonists
* Poor specimen collection
* Intralaboratory variability (Gram stain interpretation)
* Low sensitivity and specificity
* Empiric treatment guidelines
* Not cost effective

Sputum Collection
* Proper patient instruction
o Food should not have been ingested for 1-2 h prior to expectoration
o The mouth should be rinsed with saline or water
o Patient should breathe and cough deeply
o Patient should expectorate into a sterile container
* Transport container immediately to lab
* Perform Gram stain and plant specimen as soon as possible

Sputum collection
* Sputum of less than 2ml should not be processed unless obviously purulent
* Only 1 sputum per 24hr .submitted
* Some scoring system should be used to reject specimen that re oral contamination.
* Transportation in <2 hr is recommended with refrigeration if delays anticipated.
* Handle all samples using universal precautions.
* Perform Gram stain and plant specimen as soon as possible

Induced sputum
Patients who are unable to produce sputum may be assisted by respiratory therapy technician. Aerosol induced specimen are collected by allowing the patient to breath aerosolized droplets of a solution of 15% sodium chloride and 10% glycerin for approximately 10 minute . obtaining such specimen may avoid the need for a more invasive procedures ,such as bronchoscopy or needle aspiration, in many cases.

Gastric aspiration
* The gastric aspiration is used exclusively for isolation of acid-fast bacilli and may be collected from patients who are unable to produce sputum, particularly young children. The relative resistance of mycobacteria allows them to remain viable for a short period. Gastric lavage must be delivered to the lab immediately so that the acidity can be neutralized. Specimen can be first neutralized and then transported if immediate delivery is not possible.

Sputum Gram Stain Unacceptable
Sputum Gram Stain Good Quality
Good quality specimens

* Quantify number and types of inflammatory cells
* Note presence of bronchial epithelial cells
* Concentrate on areas with WBCs when looking for organisms

Read more...

Obtaining Specimens for Microbiological Evaluation



Obtaining Specimens for Microbiological Evaluation

Bacteremia I
* Most bacteremias are intermittent
* One blood culture is rarely sufficient
o Staphylococcus epidermidis
+ Frequent contaminant
+ Commonest cause of PVE
* Two blood cultures usually sufficient
o Three or four if suspect likely contaminant
o Antibiotic therapy

Blood Cultures - Volume
The magnitude of bacteremia may be low (<1cfu/ml)

Higher volumes have higher yield
Blood Cultures - Lab Aspects
* Additives (SPS, resins) increase yield
* Aerobic and anaerobic bottle = one blood culture
* Five days incubation sufficient
o Exception: Brucella, Histoplasma, Mycobacterium, Bartonella, Legionella
* Automated Systems detect CO2
o Subculture detected bottles

Aerobic/Anaerobic Blood Culture Bottles
AFB Blood Culture Bottle
Obtaining Blood Culture
* Locate the vein
* Prep kit
o Alcohol 5 sec. Dry 30-60 sec
o Tincture of Iodine-center to periphery. Dry 45-60 sec
* Remove caps, clean with alcohol
* Put on gloves
* Without palpating, draw 20 ml and put 10 in anaerobic and 10 in aerobic bottle
* Dispose of syringe in sharps container
* Label bottles and send to lab

Blood Culture Prep Kit
Sputum Culture Reliability
* Expectorated unreliable because of contamination
o Reliability  if physician observes
* Laboratory reliability screen
o > 25 PMN’s, < 10 oral squamous cells per hpf

Sputum Container

Read more...
All links posted here are collected from various websites. No video or powerpoint files are uploaded on this blog. If you are the original author and do not wish to display your content on this blog please Email me anandkumarreddy at gmail dot com I will remove it. The contents of this blog are meant for educational purpose and not for commercial use. If you use any content give due credit to the original author.

This site uses cookies from Google to deliver its services, to personalise ads and to analyse traffic. Information about your use of this site is shared with Google. By using this site, you agree to its use of cookies.

  © Blogger templates Newspaper III by Ourblogtemplates.com 2008

Back to TOP