SMI: Investigation of Throat-Related Specimens

Specimens

Throat swab, posterior pharyngeal swab, nasopharyngeal swab, pharyngeal washings, pus aspirate, oropharyngeal swab, throat gargle.

Why

To investigate upper respiratory tract infection – Pharyngitis, Tonsillitis, Epiglottitis, and Laryngitis.

Condition	Target organisms
Pharyngitis (sore throat)	1. Viral (commonest), 2. Group A Streptococcus/ Streptococcus pyogenes, 3. Group C/G Streptococcus – Streptococcus dysgalactiae subspecies equisimilis, 4. Streptococcus anginosus group, 5. Corynebacterium – C diphtheriae, C. ulcerans, 6. Vincent’s angina – Borrelia vincentii and Fusobacterium species, 7. Arcanobacterium haemolyticum, 8. Fusobacterium necrophorum. 9. Neisseria gonorrhoeae. Rare: Francisella tularensis, Yersinia enterocolitica, Mycoplasma pneumoniae and Chlamydophila pneumoniae. Other: To test for carriage – Neisseria meningitidis, Staph aureus.
Epiglottitis	1. H. influenzae type b, 2. Group A Streptococcus/ Streptococcus pyogenes, 3. Pseudomonas species and 4. Mycobacterium tuberculosis. In immunocompromised patients: Candida species and Aspergillus
Tonsillitis	1. Viral infection, 2. Some bacterial infection – Group A Streptococcus. Quinsy (peritonsillar abscess): 1. Streptococcus anginosus group, 2. Group A Streptococci, 3. Fusobacterium necrophorum and Fusobacterium nucleatum, 4. Anaerobes (Prevotella, Porphyromonas and Peptostreptococcus species), 5. S. aureus
Laryngitis	1. Viral infection, 2. Corynebacterium diphtheriae (rare), 3. MRSA, 4. Group A streptococci, 5. Streptococcus pneumoniae, 6. Haemophilus influenzae and 7. Mycobacterium tuberculosis or 8. fungal (Candida species, Blastomyces species) 9. parasite infections. Non-infectious aetiology: smoking, alcohol misuse, voice overuse, gastroesophageal reflux disease (GERD), allergies, inhalation of irritants or chemicals.

When to test for Corynebacterium diptheriae/ Corynebacterium ulcerans?

1. Membranous or pseudomembranous pharyngitis/tonsillitis
2. Contact with a confirmed case within the last 10 days
3. Travel abroad to high-risk area within the last 10 days
4. Contact with someone who has been to a high-risk area within the last 10 days
5. Contact with any animals (including household pets, visiting a farm or petting zoo) within the last 10 days
6. Recent consumption of any unpasteurised milk or dairy products
7. The patient works in a clinical microbiology laboratory, or similar occupation, where Corynebacterium species may be handled

Gram stain

Stain for Vincent’s organisms: report on Vincent’s organisms detected.

Plate selection

CONDITION	PLATE	TARGET ORGANISM
Default	Blood agar
Membrane formation or membranous pharyngitis/tonsillitis Foreign travel to high-risk areas	Hoyle’s tellurite agar	Corynebacterium diphtheriae, Corynebacterium ulcerans
Test for MSSA carriage	Blood agar, Chromogenic agar	Staph aureus
GUM clinic, gonorrhoea, N. meningitidis case or contact	GC selective agar	N. gonorrhoeae, N. meningitidis
Epiglottitis	Chocolate agar	H influenzae
Diabetes, Immunosuppressed, Oral candidiasis	Sabouraud agar OR Chromogenic aga	Yeast Mould
Persistent sore throat or Quinsy	Fastidious Anaerobic Agar (FAA) containing nalidixic acid and vancomycin	Fusobacterium necrophorum

Organisms should be isolated up to the species level, except yeast – which can be left at the yeast level. Beta-haemolytic Streptococcus should be tested by Lancefield grouping. Any C diphtheriae/ C ulcerans should be referred to the reference lab for a toxigenicity test ASAP. H influenza should be referred to the reference lab for grouping if it is epiglottitis.

Safety, infection control and public health

ORGANISM	ACTION
Corynebacterium diphtheriae, Corynebacterium ulcerans	C. diphtheriae and C. ulcerans are in Hazard Group 2. Suspected and known isolates of C. diphtheriae /C. ulcerans should always be handled in a microbiological safety cabinet. Sometimes the nature of the work may dictate that full containment Level 3 conditions should be used, e.g. for the propagation of C. diphtheriae/C. ulcerans to comply with COSHH 2004 Schedule 3 (4e). Diphtheria is a notifiable disease in the UK. – Lab should immediately inform microbiologists – The infection control team should be notified ASAP. – PHE should be notified on suspicion, on an urgent basis, for management of case, contact and outbreak. – In the healthcare setting, appropriate infection control measures should be taken. – All isolates should be referred to the reference lab for toxigenicity test.
Group A Streptococcus	The microbiologist and the infection control team should be notified. Isolate the patient for 24 – 48 h after the commencement of appropriate antibiotic therapy. Follow appropriate infection control measures as per local/national guidelines. Notify public health about any invasive group A Streptococcal infection. Ensure the isolate is sent for typing.
N meningitidis	C. diphtheriae and C. ulcerans are in Hazard Group 2. Suspected and known isolates of C. diphtheriae /C. ulcerans should always be handled in a microbiological safety cabinet. Sometimes the nature of the work may dictate that full containment Level 3 conditions should be used, e.g. for the propagation of C. diphtheriae/C. ulcerans to comply with COSHH 2004 Schedule 3 (4e). Diphtheria is a notifiable disease in the UK. – Lab should immediately inform microbiologists – The infection control team should be notified ASAP. – PHE should be notified on suspicion, on an urgent basis, for management of case, contact and outbreak. – In the healthcare setting, appropriate infection control measures should be taken. – All isolates should be referred to the reference lab for toxigenicity tests.

F tularensis is a HG3 organism.

Reference

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/423204/B_9i9.pdf