DIAGNOSTIC VALUE of MEDICAL MICROBIOLOGY

DIAGNOSTIC VALUE of
MEDICAL MICROBIOLOGY
Dr.T.V.Rao MD
21-10-2016 Dr.T.V.Rao MD @Diagnostic Microbiology 1

Read the Program with a Purpose
Every specimen needs optimal testing with
vision of scientific basis
• The program file has been made with the vision
for basic responsibilities of the Medical
Microbiologists for optimal decisions in
Diagnostic Microbiology, Every specimen reflects
the scenario in the ongoing process of infection
in the human body ( from vivo to vitro) ,
However it is important to know the predictive
value of the tests we do in the laboratory or else
the blind processing will certainly harmful if not
useful Dr.T.V.Rao
MD21-10-2016 Dr.T.V.Rao MD @Diagnostic Microbiology 2

Purpose of Diagnostic Test
in
Diagnostic Microbiology• A diagnostic test for an infectious agent can be used
to demonstrate the presence or absence of
infection, or to detect evidence of a previous
infection (for example, the presence of antibodies).
Demonstrating the presence of the infecting
organism, or a surrogate marker of infection, is often
crucial for effective clinical management and for
selecting other appropriate disease control activities
such as contact tracing.

Role of microbiology laboratory:
Introduction
The diagnosis of infections performed by
the laboratory has two important functions
•Clinical
• Diagnosis of infection in an individual patient
for everyday management of infections
•Epidemiological
• Support for infection prevention and control in
searching for source and route of transmission
of HAI
21-10-2016 4Dr.T.V.Rao MD @Diagnostic Microbiology

Minimal requirements for microbiology
services
1. Set up inside the facility
• If not possible, negotiate a contract for diagnostic
microbiology with the nearest laboratory
2. Available every day, including Sundays and
holidays
• Ideally on a 24-hour basis
3. Able to examine blood, cerebrospinal fluid,
urine, stool, wound exudate or swab,
respiratory secretions, and perform basic
serological tests (HIV, HBV, HCV)

Minimal Requirements for
microbiology services -
4. Identify common bacteria and fungi to species
level
5. Perform susceptibility testing using disc-
diffusion methodology
6. Perform basic phenotyping
• Serotyping
• Salmonellae, Shigellae, P. aeruginosa, N. meningitidis
• Bio typing
• S. typhi Shigella spp

Clinical role: Diagnosis of
infectionDiagnosis should be rapid and accurate to the species level
wherever possible
• Classical bacteriological methods
• Direct smear
• Culture
• Antigen detection
• Sensitivity testing
• Antibody detection
• Not very useful in the early stages of infection
• Molecular methods
• Rarely used in routine work for the diagnosis of bacterial HAI

Bio Safety First
•The investigators must
comply with national
workplace safety
guidelines with regard
to the safety of clinic
and laboratory
personnel and the
disposal of infectious

WHY EARLY DIAGNOSIS
• Early diagnosis and
treatment can have an
important role in
preventing the
development of long-term
complications or in
interrupting transmission of
the infectious agent.
• E.g. Tuberculosis
• Influenza

Technological advances
influences Diagnostic
Microbiology
•Recent technological
developments have led
to the proliferation of
new, rapid diagnostic
tests that hold promise
for the improved
management and control
of infectious diseases.

We must learn which test is
Optimal
• Whether these tests are
useful in a given setting
and, if so, which test is
most appropriate are
questions that can be
answered only through
evaluations in the
appropriate laboratory,
clinical or field settings.

Preparing SOPs
•SOPs should be
prepared for for all
clinical and
laboratory
procedures required
in the study

All tests must executed with a
purpose
• Evaluations of diagnostic tests
must be planned with respect to
their use for a clearly defined
purpose, carefully and
systematically executed, and
must be reported in a way that
allows the reader to understand
the study methods and the
limitations involved and to
interpret the results correctly.

Developing a plan for the study
logistics
• A plan should be developed
for safe specimen
collection, handling,
transport and storage.
Consider using pre-printed
unique study numbers for
forms and specimens Also,
develop a flow diagram for
specimen handling that can
be distributed to laboratory
staff.21-10-2016 Dr.T.V.Rao MD @Diagnostic Microbiology 14

Labelling the specimens are a
must
or just refuse the specimens
• labels should be
tested for
adherence
when samples
are frozen, if
necessary

Good sample Management a great
Boon to success

Flow Chart of Laboratory
Management of Clinical specimens

Why the laboratory Needs Clinical
Information
•No laboratory test is
complete without a
clinical Information
•No interpretation has
any clinical value if the
clinical information is
not taken into
consideration

Clinicians too should understand the
limitation of the tests
Must be reported in a
way that allows the
reader to understand
the study methods and
the limitations involved
and to interpret the
results correctly.

Principles of
Diagnostic value
specimen

Performance characteristics
• The basic performance characteristics
of a test designed to distinguish
infected from uninfected individuals
are sensitivity, that is, the probability
that a truly infected individual will
test positive, and specificity, that is,
the probability that a truly uninfected
individual will test negative. These
measures are usually expressed as a
percentage.

Think about Sensitivity and
Specificity of the test Results
• Sensitivity and specificity
are usually determined
against a reference
standard test, sometimes
referred to as a 'gold
standard' test, that is used
to identify which subjects
are truly infected and which
are uninfected.

WHAT YOU UNDERSTAND BY
GOLD STANDARD
• Errors in measuring the
sensitivity and specificity of a
test will arise if the 'gold
standard' test itself does not
have 100% sensitivity and 100%
specificity, which is not
infrequently the case. Evaluating
a diagnostic test is particularly
challenging when there is no
recognized reference standard
test.

No test can performed well without
knowing the Predictive Values
• Two other important measures
of test performance are positive
predictive value (PPV), the
probability that those testing
positive by the test are truly
infected, and negative predictive
value (NPV), the probability that
those testing negative by the
test are truly uninfected.

What is composite reference
standard
• New tests under evaluation that are
more sensitive than the existing
reference standard usually require a
composite reference standard. If a
reference standard is not available
and a composite standard cannot be
constructed, an appropriate approach
might be to report the levels of
agreement between different tests,
that is, positive by both or negative
by both.

Reporting and
disseminating results
• It is imperative that these
new diagnostics are
rigorously and properly
evaluated in the situations
in which they will be
deployed in disease
control before they are
released for general use.

Poorly performed Test is Harmful
in clinical care
• A poorly performing diagnostic
might not only waste resources
but might also impede disease
control. The basic procedures
described in this article for
designing and conducting
diagnostic evaluations provide
an outline for ensuring the
proper evaluation of new
diagnostics in laboratory and
field trials.

Role in prevention and control of
healthcare associated infections
•Outbreak
investigation
•Surveillance of HAIs
•Alert
microorganisms
reports
• Designing antibiotic
policy21-10-2016 28Dr.T.V.Rao MD @Diagnostic Microbiology

Outbreak Investigation
• To determine the cause
of a single-source
outbreak the causative
agent must be defined
• Then microbiology
laboratory determines if
two or more isolated
strains are same or
different

Additional tests during an
outbreak
• Sometimes the IP&C Team requires
additional data to clarify endemic
or epidemic situations
• Microbiological tests may be
required
• Blood products
• Environmental surfaces
• Disinfectants and antiseptics
• Air
• Water
• Hands of personnel
• Anterior nares of personnel

HAI surveillance
• The microbiology laboratory should produce routine
reports of bacterial isolates
• Allows the IPC& Team to make graphs for specific
pathogens, wards, and groups of patients
• A ‘baseline incidence’ can be established
• Any new isolate can then be compared with this incidence
• If the laboratory is computerised, these data can be
made readily available

Alert organism reports
•Identify possible agreed ‘alert’ microorganisms
• Methicillin-resistant Staphylococcus aureus (MRSA)
• Vancomycin-intermediate S.aureus (VISA)
• Vancomycin-resistant enterococci (VRE)
• MDR Pseudomonas aeruginosa
• MDR Acinetobacter baumannii
• MDR Mycobacterium tuberculosis
• ESBL enter bacteria
• Clostridium difficile

Antibiotic policy
• Regular reporting of
changing resistance patterns
–Newsletters
–Specialty specific data
• Restricted antibiotic
reporting
• Routinely only first line
antibiotics
• Reserve antibiotics only if
pathogen is resistant to first
line antibiotics21-10-2016 34Dr.T.V.Rao MD @Diagnostic Microbiology

Antibiotic stewardship
Role of Clinical Microbiologist/ID specialist
• Provide leadership to antimicrobial team
• Antibiotic ward rounds
• Interpretation of patient specific data to optimise
treatment
• culture & sensitivity
• Active surveillance/ awareness
• Screening for carriage of resistant bacteria
• Molecular detection and typing

Interpretation of Microbiology
Data
•Microbiologists interpret microbiological
data for IP&C staff
•Results of isolation, identification,
susceptibility tests, typing
•Ideally should be medical doctor specialistt
•If this is not possible, then a properly educated
scientist is required21-10-2016 36Dr.T.V.Rao MD @Diagnostic Microbiology

Role in education
• Infection prevention staff
• how to interpret
microbiological
reports/charts
• Other healthcare workers
• specimen collection and
transport, interpretation of
reports and sensitivity tests
• Students (medical and
nursing)
• basic microbiology

Please Visit me for more Clinical
Microbiology topics
• www.medmicrobes.com
• www.slideshare.com
• www.scribd.com
• www.authourstream.com
• Rao’s Microbiology and Rao’s infection on FACEBOOK
• Google search for Infectious diseases by Dr.T.V.Rao MD

References
• Evaluation of diagnostic tests for infectious diseases: general
principles Shabir Banoo et al Reviews of Microbiology
• GOOGLE resources on infectious diseases

•Program Created by Dr.T.V.Rao MD
for Medical and Paramedical
Professionals for essential learning
in Diagnostic Microbiology, as a
part of open resource for New
Generation Microbiologists
•Email
doctortvrao@gmail.com21-10-2016 Dr.T.V.Rao MD @Diagnostic Microbiology 40

DIAGNOSTIC VALUE of MEDICAL MICROBIOLOGY

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