Infectious Diseases Diagnostics Overview
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Questions and Answers

What is the primary benefit of using PCR amplification over direct hybridisation for nucleic acid detection?

  • Less time-consuming process
  • Higher sensitivity and specificity (correct)
  • Lower cost of materials
  • Ability to detect only one pathogen

Which statement best describes the use of nucleic acid tests in clinical settings?

  • They are primarily used to confirm antibiotic treatment.
  • They provide rapid and accurate diagnosis of multiple pathogens. (correct)
  • They can only be used on blood samples.
  • They can identify bacterial infections only.

In what way does advancing technology impact nucleic acid testing?

  • It enhances the rapid turnaround and cost-effectiveness. (correct)
  • It limits tests to only viral detections.
  • It increases the frequency of false negatives.
  • It reduces the need for specificity in tests.

What is a key application of nucleic acid tests in public health?

<p>Detecting antimicrobial resistance (B)</p> Signup and view all the answers

Which of the following is NOT a characteristic of nucleic acid tests?

<p>They offer low specificity. (B)</p> Signup and view all the answers

What is a key limitation of using light microscopy for viral detection?

<p>Viruses are not visible on light microscopy. (A)</p> Signup and view all the answers

What does light microscopy primarily allow for in clinical diagnostics?

<p>Direct visualization of microorganisms (B)</p> Signup and view all the answers

Which method is primarily used for diagnosing respiratory viruses?

<p>Nucleic acid amplification - PCR (B)</p> Signup and view all the answers

Which limitation is associated with light microscopy?

<p>It requires a specimen containing sufficient microorganisms for detection. (B)</p> Signup and view all the answers

What does serology primarily help to confirm?

<p>Immunity from past infection or immunisation (B)</p> Signup and view all the answers

Which statement about HIV and antigen detection is true?

<p>HIV antigen can be positive before antibody detection. (D)</p> Signup and view all the answers

Why is electron microscopy no longer in routine clinical use?

<p>It is expensive and requires specialized interpretation. (A)</p> Signup and view all the answers

What is the purpose of nucleic acid amplification techniques like PCR in viral diagnostics?

<p>To detect early viral infections. (C)</p> Signup and view all the answers

What technique uses antibodies against specific antigens to identify pathogens?

<p>Immunostaining (A)</p> Signup and view all the answers

What is the primary outcome of fluorescein conjugated immunoglobulin staining?

<p>Visual confirmation of herpes simplex virus type-2 infection (C)</p> Signup and view all the answers

What does the specificity of light microscopy depend upon?

<p>The presence of non-pathogenic organisms in samples from non-sterile sites (A)</p> Signup and view all the answers

Which statement about electron microscopy is incorrect?

<p>It is now widely used in routine clinical diagnosis. (A)</p> Signup and view all the answers

Which method is most suitable for quickly identifying pathogens in specific settings?

<p>Immunostaining (C)</p> Signup and view all the answers

What is the purpose of the fluid added to the nasal or pharyngeal swab in COVID-19 antigen detection?

<p>To solubilize viral antigens (B)</p> Signup and view all the answers

Which term describes the time period when antibodies may not be detectable during an infection?

<p>Window period (C)</p> Signup and view all the answers

What is the sensitivity range of COVID-19 antigen tests?

<p>70-75% (B)</p> Signup and view all the answers

What does IgM positivity indicate in the context of antibody responses?

<p>Acute or recent infection (C)</p> Signup and view all the answers

Which type of antibodies do serological tests primarily measure?

<p>IgM, IgG, IgA, and IgE (D)</p> Signup and view all the answers

What is a limitation of serological tests in detecting infections?

<p>Interpreting results can be complex due to cross-reactivity (B)</p> Signup and view all the answers

During a chronic infection, what would typically be the IgM and IgG status?

<p>IgM negative and IgG positive (C)</p> Signup and view all the answers

What is the mainstay method for diagnosing and identifying fungi?

<p>Culture (B)</p> Signup and view all the answers

Which of the following fungal antigens is associated with aspergillus infection?

<p>Galactomannan (B)</p> Signup and view all the answers

Why is serology for diagnosing fungal infections challenging in endemic areas?

<p>Previous infections complicate interpretation. (C)</p> Signup and view all the answers

Which test is commonly used for diagnosing malaria?

<p>Microscopy of blood samples (B)</p> Signup and view all the answers

What is a key limitation in culturing parasites?

<p>They cannot be cultured in vitro. (C)</p> Signup and view all the answers

Which of the following methods may detect multiple types of fungi?

<p>Nucleic acid amplification - PCR (D)</p> Signup and view all the answers

What is one of the challenges associated with serology for parasitic infections?

<p>Difficult interpretation due to past infections (D)</p> Signup and view all the answers

Which method is not commonly used for diagnosing parasitic infections?

<p>Culture (B)</p> Signup and view all the answers

What is one of the benefits of achieving a definitive diagnosis in infections?

<p>Supports public health measures (C)</p> Signup and view all the answers

Which diagnostic method involves visualizing and sampling the bronchi?

<p>Bronchoscopy (D)</p> Signup and view all the answers

What component is part of the fungal cell wall that can be significant in diagnosing fungal infections?

<p>Beta-glucan (D)</p> Signup and view all the answers

Which organism is commonly known for causing minor infections but can also lead to serious diseases?

<p>Candida (D)</p> Signup and view all the answers

What fluid surrounds the brain and spinal cord, and can be a site for unusual infections?

<p>Cerebrospinal fluid (A)</p> Signup and view all the answers

What technology can be utilized to amplify nucleic acids for diagnosing infections?

<p>Polymerase chain reaction (PCR) (C)</p> Signup and view all the answers

Which virus is known for usually causing mild symptoms but can lead to serious disease in immunocompromised individuals?

<p>Cytomegalovirus (A)</p> Signup and view all the answers

What is the primary purpose of using serology in diagnosing infections?

<p>To detect antibodies produced in response to infections (D)</p> Signup and view all the answers

Flashcards

Light Microscopy for Microbes

A method to directly view bacteria, fungi, and parasites using stained or unstained samples. It's quick but its ability to pinpoint the exact microorganism isn't definitive and might miss non-pathogens.

Light Microscopy Limitations

Light microscopy has limited sensitivity (needs a lot of microbes) and specificity (might identify non-pathogens). It's also not for detailed identification or antimicrobial sensitivity testing.

Electron Microscopy History

Electron microscopy was once the main tool for rapidly diagnosing viruses, but is now less common in clinical settings because of cost and specialty interpretation needed.

Immunostaining Technique

A technique using antibodies to precisely target and detect specific pathogens (like viruses) in tissue samples.

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Immunostaining Application

Immunostaining specifically helps confirm or identify a viral infection, say, herpes, by revealing its presence in cells that have been exposed to the targeted antibody.

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Immunostaining Advantages

Immunostaining provides high specificity targeting a desired microbe or antigen, avoiding a false positive from a wider range of organisms.

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Fluorescence Microscopy in Immunostaining

In immunostaining, fluorescent dyes like FITC are often used to label antibody-bound targets to easily visualize and pinpoint the pathogen in the light microscope.

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Electron Microscopy Use

Previously used to quickly identify viruses. This method is no longer commonly used as a primary diagnostic tool for routine clinical use.

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Antigen Detection Test (COVID-19)

A rapid test that detects viral antigens in a sample, like a nasal swab.

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Capillary Action (COVID-19 test)

The movement of fluid through the test chamber due to surface tension.

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Antibodies (COVID-19)

Proteins that bind to specific antigens.

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Serological Test

A blood test to measure antibodies (IgM, IgG, IgA, IgE) to detect immune response.

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Window Period (Serology)

Time when antibodies are not yet detectable after infection.

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IgM

An antibody that is typically present in the early stages of an infection.

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IgG

An antibody produced later in infection or from past exposure, indicating ongoing or past infection.

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Sensitivity (COVID-19 Test)

The proportion of infected individuals correctly identified by the test.

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Nucleic acid tests

Tests used to detect pathogens and other organisms in biological samples.

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Rapid diagnosis

A quick way to identify an illness or pathogen.

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Pathogen detection

Techniques used to discover and identify disease-causing microorganisms.

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Antimicrobial resistance

The ability of microorganisms to withstand the effects of drugs or medicines meant to kill them.

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Viral Diagnosis Methods

Methods used to identify and diagnose viral infections.

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Antigen Detection

Identifying viral antigens (parts of the virus).

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Nucleic Acid Amplification (PCR)

A method to detect viral genetic material (DNA or RNA).

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Serology

Blood test to identify antibodies produced against the virus.

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Antiviral Resistance

When viruses adapt to avoid antiviral drugs.

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Empirical treatment

Treating an infection based on symptoms and clinical judgment, without waiting for lab results.

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Definitive diagnosis

Identifying the specific microbe causing an infection, using laboratory tests.

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Microscopy

Using a microscope to visualize microbes directly in a sample.

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Culture

Growing microbes in a controlled environment to identify them.

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Nucleic acid amplification

Copying DNA or RNA to increase the amount of genetic material for diagnosis.

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Antimicrobial sensitivity testing

Determining which antibiotics are effective against a specific microbe.

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Fungal Microscopy

Identifying fungal elements (yeasts or molds) in clinical samples using a microscope.

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Fungal Culture

Growing fungi in a controlled environment to identify them and test their sensitivity to antifungal drugs.

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Fungal Antigen Detection

Identifying specific fungal components (like galactomannan or beta-glucan) in body fluids.

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Fungal PCR

Using polymerase chain reaction to detect fungal DNA in samples.

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Parasite Microscopy

Examining samples (blood, urine, stool) under a microscope to identify parasites.

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Parasite Antigen Detection

Rapidly detecting parasite antigens in blood (like malaria) or other samples.

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Parasite Culture

Not possible to grow parasites in a lab setting.

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Parasite PCR

Detecting parasite DNA in samples using PCR.

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Study Notes

Viruses, Fungal and Parasitic Infections

  • Diagnostic tests are used in infectious diseases
  • This session reviews tests available for diagnosis of infectious disease
  • The tests complement clinical skills for targeting appropriate therapy
  • The session includes tests for bacteria, viruses, fungi, and parasites
  • Clinical examples illustrate the use of tests

Why is it important to identify the organism?

  • Improve patient outcome
    • Correct diagnosis
    • Best antibiotic choice
    • Reduce antimicrobial resistance risks
    • Awareness of complications (eye involvement in CMV)
      • Immunocompromised host
  • Public health
    • Regional and global surveillance
      • Emergence and spread of high-risk pathogens
    • Contact tracing
    • Surveillance
      • Meningitis, tuberculosis
      • Salmonella gastroenteritis (linked to a restaurant)

Samples

  • Easily collected
    • Urine
    • Blood
    • Stool
    • Sputum
    • Swabs (wounds, skin, throat, urethra)
    • Pus draining from abscesses
  • Invasive samples (for complex cases)
    • Samples from deep in the lungs (bronchoscope)
    • Cerebrospinal fluid (lumbar puncture)
    • Bone marrow biopsy
    • Deep tissue or abscess samples (image-guided aspiration or biopsy)

Types of Tests

  • Microscopy
    • Direct visualization of microorganisms
    • Unstained or stained preparations
    • Morphology and staining characteristics for identification suggestions
    • Limited sensitivity
    • Limited specificity (non-pathogenic organisms in non-sterile samples)
    • Rapid
    • No definitive identification
    • No antimicrobial sensitivity data
  • Electron microscopy (viruses)
    • Visualizes viruses
    • Expensive, specialized interpretation
    • Not routinely used
  • Antigen detection
    • Identifies antigens specific to organisms
    • Rapid and specific immunoassay
    • Easy to perform
    • Point-of-care tests available
    • Not affected by antibiotics
    • Can only detect one organism per test
    • Less sensitive than molecular techniques
    • No antimicrobial sensitivity data
  • Culture
    • Grows microorganisms in the laboratory
    • Appearance of colonies in vitro to help identify
    • More detailed diagnostic tests (metabolism, biochemical phenotype)
    • Anti-microbial sensitivity testing
  • Immunological tests
    • Measures immune response to specific antigens
  • Nucleic acid detection
    • Amplifies sequences of RNA or DNA
    • Specific to individual organisms

Antigen Detection Example - COVID-19

  • Nasal/pharyngeal swab placed in fluid
  • Fluid solubilizes viral antigens
  • Fluid is added for sample
  • Antigens captured by specific antibodies embedded in testing chamber floor
  • Color change visualizes with control and test lines
  • Sensitivity: 70-75%
  • Specificity: 98-99%

Serological Tests

  • Measures immunoglobulins (IgM, IgG, IgA, IgE)
  • Evidence that an individual has mounted an immune response
  • Does not necessarily indicate active infection
  • Negative early in the infection (before antibody is detectable) - window period
  • May be difficult to interpret
    • Cross-reacting antibodies between similar organisms/species
    • Distinguishing active from past infection/immunization
    • Poor antibody responses in severely immunocompromised individuals

Antibody Response Dynamics

  • Shows IgM and IgG/IgA over time
  • Pattern in graph varies with acute, past, or chronic infection

Nucleic Acid Detection - The Way Forward

  • Direct hybridization of DNA/RNA lacks sensitivity
  • PCR amplification is common in practice
    • Used with many biological specimens
    • Detects multiple pathogens from the same specimen
    • Technology improves rapidity and cost-effectiveness
  • Uses
    • Rapid accurate diagnosis
    • Detection of antimicrobial resistance
    • Improved clinical decision-making
    • Identify new emerging pathogens
    • Genomic information

Contact Information

Glossary

  • Terms related to viruses, fungal and parasitic infections

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Description

This quiz explores the diagnostic tests used for various infectious diseases including viruses, bacteria, fungi, and parasites. It emphasizes the importance of correct diagnostics for improving patient outcomes and public health surveillance. Clinical examples will help illustrate the real-world applications of these tests.

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