Whenever possible throat and mouth swabs should be collected by a medical officer or experienced nurse. The medical instruments and containers used in specimen collection must be sterile and transport conditions must be devoid of contamination.
1. In a good light and using the handle of a spoon to depress the tongue, examine the inside of the mouth. Look for inflammation, and the presence of any membrane, exudate, or pus.
- With diphtheria, a grayish-yellow membrane (later becoming grayish green-black and smelly) can often be seen extending forward over the soft palate and backwards on the pharyngeal wall.
- With a streptococcal sore throat, the tonsils are inflamed and often covered in yellow spots.
- With C. albicans infection, patches of white exudates may be seen attached in places to the mucous membrane of the mouth.
- With Vincent’s angina, there is ulceration of the mouth, throat, or lips. Viral tonsillitis can also cause ulceration of the tonsils.
2. Swab the affected area using a sterile cotton-wool swab. Taking care not to contaminate the swab with saliva, return it to its sterile container.
Important: For 8 hours before swabbing, the patient must not be treated with antibiotics or antiseptic mouth washes (gargles).
Caution: It can be dangerous to collect a throat and mouth swabs from a child with acute haemophilus epiglottitis because this may cause a spasm that can obstruct the child’s airway. Blood for culture should be collected instead.
3. Within two hours of collection, deliver the swab with a completed request form to the laboratory.
In a Health Centre for Dispatch to a Microbiology Laboratory
1. Using a sterile swab (supplied in a tube of silica gel by the microbiology laboratory), collect a specimen from the infected area as described under the hospital collection of throat swabs.
2. Taking care not to contaminate the swab, return it to its tube. Seal with adhesive tape and label the tube.
3. Send the swab with a completed request form to reach the microbiology laboratory within 3 days.
Transport of Swabs in Tubes containing Silica Gel
It has been shown that S. pyogenes will remain viable for at least 3 days (at ambient temperatures) on swabs stored in tubes containing 3 – 5g of dessicated silica gel.
Note: Other systems for transporting specimens to be investigated for S. pyogenes are described in the WHO publication Laboratory diagnosis for group A streptococcal infections.
Gram positive Gram negative
Streptococcus pyogenes Vincent’s organisms
Respiratory viruses, enteroviruses and herpes simplex virus type 1
Candida albicans and other yeasts
Note: Pathogens in the upper respiratory tract such as Bordetella pertussis, Streptococcus pneumonia and Neisseria meningitidis, are usually more successfully isolated from naso-pharyngeal secretions collected by aspiration.
Notes On Pathogens
- Pyogenes, Lancefield Group A beta-haemolytic Streptococcus is the commonest cause of bacterial pharyngitis (sore throat), especially in young children. Its association with rheumatic heart disease and importance in developing countries are have been a subject of great research. The term scarlet fever is used when streptococcal pharynigitis is accompanied by a characteristic skin rush.
- diphtheria produces a powerful and often fatal exotoxin and therefore when diphtheria is suspected, the patient is treated immediately with antitoxin. The role of the laboratory is to confirm the clinical diagnosis.
- albicans infection of the mouth (oral thrush) is common in those with HIV disease. It may affect young children, those who have been treated with antibiotics for a long period, and occasionally diabetes and those with other systemic diseases.
Gram Positive Gram Negative
Viridans streptococci Moraxella catarrhalis
Non-haemolytic streptococci Neisseria pharyngitidis
Streptococcus pneumonia Coliforms
Staphylococcus epidermidis Bacteroides species
Micrococci Haemophilus influenza
Lactobacilli Diphtheroids (mostly non-capsulate strains)
Also various spirochaetes, actinomycetes, aerobic and anaerobic spore-bearers, and yeasts.
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