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Flashcards in SAS/Review Deck (198)
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What is the most important consideratio when interpreting a positive IgM for pertussis?

(Ex: What could cause an inaccurate test result?)

If the patient was recently immunized with acellular pertussis vaccine, they may have a positive IgM test result without actually having the illness


If an infant has a pertussis infection, what laboratory findings would you expect to find 4 weeks after the start of symptoms


IgM: (positive or negative)

IgG: (positive or negative) 


4 weeks after the start of symptoms...

IgM = positive

IgG = positive


IgM is present at the beginning of a new infection. 4 weeks is long enough for class switching to have occured to produce IgG as well



Bacteria X has a very short incubation period. 

Assuming serology and PCR can both detect the presence of Bacteria X, which test will provide results soonest after the onset of symptoms? 

PCR (from sputum or pus sample)

Serology studies examine antibody production, so the immune response must be fully functional for results to be accurate


Which T-cell subset is most important in driving the increased production of IgG and IgA antibodies in response to a pertussis infection? 

CD4+ Th2 Helper T-cells



Your body has lots of IgA floating around in it right now

Compare the affinity of IgA for B. pertussis produced by a plasma cell after infection with the affinity of IgM on a naive B-cell before infection 


The IgA produced by the plasma cells after a B. pertussis infection is most likely has a higher affinity than the original IgM produced by a naive B cell

The original IgM has some affinity for B. pertussis

Upon infection, Th2 CD4+ helper T-cells are activated by APCs (Bind antigen on MHC II, CD40:CD40L interaction) to form a germinal center and release cytokines

  • This promotes both class switching from IgM -> IgA and somatic hypermutation
    • Somatic hypermutation and selection by folicular dendritic cells will select for the IgA antibodies with the highest affinity for B. pertussis antigen


What is the principle reason to treat B. pertussis with antibiotics?

To limit the risk of secondary spread

Antibiotic treatment does not greatly affect the course of the disease for the infected individual


Compare the locations of primary and reactivation tuberculosis

Primary typically takes hold in the mid/lower lobe

Reactivation TB typically occurs in the apex of the lung


Which test for tuberculosis will tell you if an individual has a latent infection?

a) Tuberculin skin test

b) Interferon-gamma release assay

c) Nucleic acid amplification

d) Solid media

e) Liquid broth

a) Tuberculin skin test - But may cross react if the patient had any mycoplasm infection or the BCG vaccine

b) Interferon-gamma release assay

c) Nucleic acid amplification

d) Solid media

e) Liquid broth

Both answers in bold are correct


Which test for tuberculosis will most rapidly confirm a diagnosis of an active TB infection?

a) Tuberculin skin test

b) Interferon-gamma release assay

c) Nucleic acid amplification

d) Solid media

e) Liquid broth

  • a) Tuberculin skin test
    • 48-72 hours
    • Will tell you if exposed not necessarily if infection is active
  • b) Interferon-gamma release assay
    • 24-48h
    • Indicates immune response, but not necessarily active infection 
  • c) Nucleic acid amplification
    • ​Results in 1-2 hours
  • d) Solid media
    • Weeks
  • e) Liquid broth
    • Weeks



Which cells are most critical in controlling the growth of M. tuberculosis?

CD4+ Th1 Helper T-cells

(Combat intracellular pathogens; in the case of MTB, they mediate the granulomatous response)


A patient who does not have an active infection are concerned about possible exposure to M. tuberculosis. 

Which test is recommended? When?

  • Interferon gamma release assay two months after last suspected contact
    • Testing sooner may give a false negative
  • Tuberculin skin test
    • False positive is more likely (test has low specificity)


A 5 year-old boy presents with a fever, knee pain, and this rash

Which encapsulated, gram-negative diplococcus is the likely cause of this infection? 

Neisseria meningitidis


Which test tube represents the growth of E. coli?

Test tube 3

E. coli is an facultative aerobe; it can grow near the top of the liquid near the oxygen, but it can also survive without it and grow everywhere


Which test tube represents the growth of Neisseria meningitidis?

Test tube 1

Neisseria meningitidis is an obligate aerobe; will need oxygen, which is located near the surface of the liquid


Increased susceptibility to Neisseria is asosciated with deficiencies in which components of the immune system?

Complement proteins from C5-C9; deficiencies of these complement proteins prevent the formation of the membrane-attack complex (MAC) (via the classic pathway) that is required to kill neisseria

Deficiencies in Factor D and properdin, required for the alternate complement pathway, also result in increased risk of Neisserial infections 

Infections are likely to be recurrent and invasive


52 year old Hatian immigrant presents with fever, profuse sweating, labile hypertension, tachycardia, and facial spasms. Loud noises cause him to contrort his body in muscle spasms. 

What is the likely causative agent of his symptoms?

Clostridium tetani

He has tetanus


A patient who immigrated from the Democratic Republic of the Congo last year presents with a tetanus infection. 

Which treatment should be given immediately?

Injection of tetanus immunoglobulin to confer passive immunity to the patient

- Works rapidly (faster than Tdap vaccine)

(Tdap vaccine should be given to prevent subsequent infection)


22 yo presents with sudden onset of bloody diarrhea and abdominal cramps.  He treats himself with some ciprofloxacin he has left over from a trip to Mexico.  The diarrhea improves but he becomes more ill with cramping in his lower back, bloody urine and severe fatigue.  On presentation to the ED, he is found to have anemia, thrombocytopenia and renal failure.  What is the cause of his illness?

Shiga-like toxin, produced by enterohemorrhagic E. coli (EHEC)

  • Associated with travel to Mexico


A patient presents with blurry vision, trouble swallowing and speaking, and labored breathing. 

Which of the following toxins might be causing her symptoms?

A. Staphylococcal enterotoxin

B. Botulinum toxin

C. Tetanus toxin

D. Diphtheria toxin

B. Botulinum toxin

Symptoms are associated with flaccid paralysis

(Would be an even stronger connection if people who had eaten the same poorly canned food all presented together)


Which bacteria secrete Shiga-like toxin?

What is the effect of the toxin?

EHEC - Patients present with bloody diarrhea

Shiga-like toxin binds to globotriaosyceramide (BG3) in kidney and CNS

It inhibits the 60S unit of the bacterial ribosome to inhibit protein synthesis and cause cell death


Which cells in the body does tetanus toxin bind to?

What is the effect?

Tetanus toxin binds to presynaptic inhibitory motor nerve endings (Renshaw cells) to block the release of GABA and glycine (inhibitory neurotransmitters)

The result is constant muscle contraction; lockjaw, muscle spasm


Which cells in the body does botulinum toxin bind to? 

What is the effect?


Botulinum toxin binds to presynaptic motor end plates, preventing ACh release

The result is flaccid paralysis (Blurry vision, impaired swallowing/speaking, may lead to difficulty breathing)


Describe the mechanism of action of diphtheria toxin.

What is the effect on patients?

Diphtheria toxin ADP-ribosylates EF-2, inhibiting protein synthesis

This leads to cell necrosis and pseudomembrane formation in the oropharynx, palate, nasopharynx, nose, and larynx; patients will present with sore throat, fever, difficulty swallowing, hoarseness, and rhinorrhea

Most often seen in children or immigrants who were not vaccinated



Which assay would be most useful to evaluate for the presence of HIV antigens and antibodies

Combination ELISA (aka immunoassay); can test for both antigens andtibodies at the same time

Nephelometry can do both, but not at the same time


A patient presents with 3 days of painful rash (shown below) that is isolated on his right buttock and thigh

He is not taking any medications and reports no allergies

What is the most likely cause of this rash?


Varicella Zoster Virus

- Isolated; does not cross midline

-  Painful



You are treating a 35 year old patient with shingles. 

What illness did this patient likely have as a child?

What is unusual or concerning about this presentation?


The patient likely had chicken pox (Varicella zoster virus) as a child; shingles is a reactivation of VZV

The presentation of shingles in this patient is concerning because they are young; VZV usually re-activates when the patient's T-cell function is less than optimal, which happens naturally with age. 

Because the patient is young, we might suspect a pathology that is suppressing the function of T-cells


 Which test would be most useful to determine a patient's CD4+ T-cell count?

Flow cytometry


Which patients should not recieve vaccines for MMR, smallpox, and chickenpox?

Patients who are immunosuppressed;

These vaccines are all live, attenuated virus vaccines; they are likely to cause illness in anyone who is immunosuppressed


Which rashe is typically only found in patients with advanced HIV/AIDS?

HHV-8 (Kaposi sarcoma)



Which agent is used to treat pneumocystis?


Although pneumocystis is a fungus, it must be treated wtih trimethoprim-sulfamethoxazole; other anti-fungal agents won't work