M4 Upper Respiratory Tract Infections Flashcards
What areas of the body does the upper respiratory tract include?
The nose, pharynx, and larynx.
What is pharyngitis?
Pharyngitis - Inflammation of the pharynx, hypopharynx, uvula, and tonsils.
Note: Slide 3 includes lots of URT infections like Rhinitis, Rhino-sinusitis or sinusitis, Nasopharyngitis (rhino-pharyngitis or the common cold), Epiglottitis (supraglottitis), Laryngitis, Laryngotracheitis and Tracheitis but we are focusing on pharyngitis.
What factors for defense do some virulent strains of Gr. A Strep posses?
Virulent strains possess a variety of factors for defense,
1. Adherence and
2. Invasion (M protein- hyaluronic acid- streptolysins O & S- hyaluronidase)
What do some Gr. A Strep strains possess that cause systemic illness?
Exotoxins
Some strains possess exotoxins that can progress from pharyngitis → systemic illness (scarlet fever, systemic shock syndrome)
What are the complications that can be from a Strep. Gr. A infection?
-Acute Glomerulonephritis (IgG & other antibodies involved collect in glomeruli in kidneys (hematuria, proteinuria, RBC casts)
-Acute Rheumatic fever (after strep throat, antibodies involved heart, joints, skin, brain). More common in children 5-15. Damages heart valves.
- Scarlet fever from exotoxins
- Acute pharyngitis
How many typical normal flora can you name (for >50% of the people)?
Viridans streptococci
Neisseria sp., Moraxella spp.
Corynebacteria
Bacteroides
Anaerobic cocci (Veillonella)
Fusiform bacteria
Candida albicans
Streptococcus mutans
Haemophilus influenzae
What are some occasional surprising residents of the URT (these people would then be carriers of these bacteria)?
Streptococcus pyogenes
Streptococcus pneumoniae
Neisseria meningitidis
What are some uncommon residents that <1% of people have?
Corynebacterium diphtheriae
Klebsiella pneumoniae
And esp. after antibiotic treatment
- Pseudomonas
- E. coli
- Candida albicans
What are the transport/storage requirements for throat swabs for routine pharyngitis?
Routine pharyngitis
1. Throat swab normally received in transport media
2. stable for 4 hrs at room temperature
3. refrigerate up to 24 hours
How should throat swabs received for direct antigen detection be received?
Swabs received for “Direct Antigen Detection” should be dry
Do you need to culture if your swab direct antigen test for Gr. A Strep is positive?
Highly specific (if +, no need for culture)
What happens if your direct antigen test for Gr. A Strep is negative?
Not so highly sensitive (If neg–>culture).
Note: Direct Antigen test: swab against Antibodies for Strep A (only!).
What plate do you plant throat swab specimens? Incubation?
Planting: BA plate in CO2 (in theory: ideally anaerobic).
Some Labs add a Bacitracin disk (TAXOS A) or use media with it, why?
Strep A is susceptible to bacitracin, then you can see this halo (zone of inhibition’s) that will tell you it is GAS. But if the organism is in low amounts then it is hard to tell if it is R or S. In rare cases it can inhibit Strep A. So not a common practice any more.
Some labs make cuts in the agar, why?
Some labs make cuts in the agar, to allow for the streptolysins to show they are beta-hem.
Do we need a direct smear for URT specimens?
A direct smear does not help to differentiate the Streptococcus species, so we do not do the direct smears (i.e. smear directly from the patient sample).
Note: She mentioned an exception to this in class.
What are we looking for on our BA plate for throat swabs?
Culture:
Looking for beta-hem colonies:
Strep Group A (pyogenes), C & G (dysgalactiae)
Arcanobacterium haemolyticus (rare): GPB!