Lab 4 Upper Respiratory Tract Infections Flashcards
(39 cards)
What are the only routine pathogens looked at in a throat swab culture?
Throat swab culture:
- Beta hemolytic Streptococci Group A, C, G, (or Streptococcus pyogenes and Strep dysgalactiae)
but primarily Strep Group A.
What media and incubation environment are typically used? Is that the ideal conditions?
Throat swabs are planted on BA and usually incubated in CO2 even though ideal conditions would be anaerobic.
Can other pathogens (other than Strep Group A, C and G be cultured? Why?
Yes on request because they need specific media.
Neisseria gonorrhoeae needs Thayer Martin to inhibit normal flora.
Corynebacterium diphtheria needs Tinsdale agar.
Why is routine AST not needed for beta hemolytic Strep?
Penicillin is the recommended treatment and no resistance has been found to it.
If a patient is allergic to penicillin then AST could be performed on MH blood following CLSI method.
What are the symptoms of pharyngitis?
Fever, extremely red and perhaps swollen throat, and tonsillar exudate (pus) typically characterize pharyngitis.
Is it easy to diagnose pharyngitis from clinical appearance alone?
It is very difficult to make a diagnosis from clinical appearance alone; therefore a swab must be taken.
What secondary infection/conditions are some people at risk of from Gr. A Strep?
Group A strep may SECONDARILY infect wounds from trauma and produce scarlet fever.
Other major concerns (non-pus forming conditions) are:
- acute rheumatic fever
- acute glomerulonephritis, also
- streptococcal toxic-shock like syndrome
Why may Group A Strep (GAS) cause scarlet fever?
GAS elaborate an erythrogenic toxin that may produce scarlet fever, which is characterized by a scarlatina-like rash that affects the trunk, neck and extremities.
Why is it important to select a method to diagnose Group A Strep with optimal sensitivity?
It is important to select methods of optimal sensitivity, since a low number of GAS in a specimen does not necessarily indicate colonization and may represent infection. If the method is not too sensitive, it might be missed.
What symptoms can Group C and G beta-haemolytic Strep cause?
Group C & G beta-haemolytic streptococci can cause pharyngitis and fever.
What secondary condition are patients not at risk from a Group C and G Strep infection that they are with Group A?
Group C & G Strep do not place patients at risk of acute rheumatic fever.
What is Diphtheria and what bacteria causes it? What is its classic symptom?
Diphtheria is an acute infectious disease primarily of the upper respiratory tract but occasionally of the skin. It is caused by toxigenic strains of Corynebacterium diphtheria.
The disease is shown by a classic pseudomembrane of the pharynx; however, this symptom may be lacking in mild cases.
What test is done and media used to confirm a diagnosis of diphtheria?
To confirm a clinical diagnosis of diphtheria, the strain isolated must be shown to produce toxin= Elek test (done in reference labs).
Tinsdale medium is a selective and differential medium to isolate and presumptively identify C. diphtheria strains.
Which organisms cause upper respiratory infections?
The most common cause of bacterial pharyngitis (bacterial sore throat, not viral), in North America is Streptococcus pyogenes- Group A streptococci (GAS). Other bacterial causes of pharyngitis include beta hemolytic Group C and G streptococci, Neisseria gonorrhoeae, Corynebacterium diphtheria, and Arcanobacterium haemolyticum.
Which are the usual “normal flora” organisms?
Resident Microbiota of the URT: Coag neg Staph, Viridans Strep, Corynebacterium, non pathogenic Neisseria spp.
What are the steps for taking an acceptable throat swab specimen from the tonsillar area and/or posterior pharynx?
- Depress tongue gently with tongue depressor.
- Extend sterile Dacron-tip swab between the tonsillar pillars and behind the uvula. (avoid touching the cheeks, tongue, uvula, or lips)
- Sweep the swab back and forth across the posterior pharynx, tonsillar areas, and any inflamed or ulcerated areas to obtain sample.
What should be avoided when taking a throat swab from the tonsillar area and/or posterior pharynx?
Avoid the tongue and uvula, is recommended.
Do not obtain throat samples if epiglottis is inflamed, as sampling may cause serious respiratory obstruction.
Do Streptococci survive well in a dry environment?
Yes, Streptococci survive well in a dry environment, and the original numbers present in the throat are preserved.
When is a transport medium needed for a throat swab specimen?
If the specimen is transported over a distance or not being processed until the next day or is to be tested for other pathogens, then a swab in transport medium should be used.
Is a nasopharyngeal specimen also acceptable and how is it obtained? What other types of nasopharyngeal specimens could be acceptable?
A nasopharyngeal specimen is also acceptable and is obtained using a flexible-wire calcium alginate-tipped swab through the nose or up the back of the throat into the posterior nasopharynx.
What other types of nasopharyngeal specimens could be acceptable?
Nasopharyngeal suction or sinus aspirates are also acceptable, provided they are obtained aseptically and kept moist.
When is a ‘dry’ throat swab not acceptable?
- If > 2 hrs has passed after collection. A ‘dry’ swab is sufficient if no more than 2 hours is expected to elapse between the time the swab specimen is collected and the time it is examined in the laboratory.
- Demographic mismatches between requisition and sample and lack of basic patient information
- Frozen sample or leaking specimen
What are the requirements for media to help isolate Streptococci?
Care must be taken in choosing an appropriate medium for isolation.
- Free of reducing sugars
- pH of media between 7.3 and 7.4
Note re #1: Streptococci require media free of reducing sugars i.e. substances that influence the expression of beta-hemolysis by strep-for example glucose. (eg. enriched infusion agar-such as tryptic soy, heart infusion, Todd-Hewitt- or protease peptone are free from reducing sugars)
What media type is recommended to help isolate Streptococcus and why?
Sheep blood is recommended to prevent the growth of Haemophilus haemolyticus, which, if present in a throat specimen, has a colonial morphology indistinguishable from that of beta-hemolytic streptococci. This blood lacks sufficient amounts of pyridine nucleotides ( V factor) to support the growth of H. haemolyticus.
