Pharyngitis is inflammation of the pharynx, and when the tonsils are visibly involved the same illness is called tonsillitis or pharyngotonsillitis. The distinction is anatomical rather than diagnostic, and it matters less than the question the illness actually poses: is there a bacterium here that needs an antibiotic, and which one?
Most acute pharyngitis in children is viral. Streptococcus pyogenes, or group A Streptococcus (GAS), is found in roughly 1 in 4 children presenting with acute pharyngitis, with pooled estimates across diagnostic studies spanning 20% to 40%. Carriage complicates the count: 10% to 21% of children with microbiological evidence of GAS are asymptomatic carriers, in whom the organism lives in the throat without causing the acute illness. Globally, streptococcal pharyngitis accounts for an estimated 288.6 million episodes a year in children aged 5–14 years.
The teaching shorthand for the split is about two-thirds viral and about one-third bacterial, with GAS responsible for roughly 90% of the bacterial cases. The exact proportions vary with age, season, epidemic activity and how hard the laboratory looks, so the numbers are a starting point for the differential, not a fixed law.
| Group | Roughly | Typical agents |
|---|---|---|
| Viruses | Two-thirds of cases | Adenovirus (the commonest single viral cause), influenza A and B, parainfluenza 1–4, Epstein–Barr virus (EBV), enteroviruses, herpes simplex virus, respiratory syncytial virus, rhinoviruses |
| Bacteria | One-third of cases | Streptococcus pyogenes (GAS) — about 90% of bacterial cases; other β-haemolytic streptococci (groups B, C and G); Mycoplasma pneumoniae; Haemophilus influenzae; Neisseria meningitidis; Neisseria gonorrhoeae |
Two points qualify the table. Pediatric tonsillitis caused by SARS-CoV-2 is uncommon and does not belong near the top of this differential. And group B Streptococcus, although it appears among the other streptococci, causes neonatal sepsis acquired from the mother during delivery. It does not cause pharyngitis in the school-age child and is not the target of the swab-and-treat logic.
One group in the table carries consequences out of proportion to its share of cases. Group A Streptococcus is a Gram-positive coccus that grows in chains, and it is the reason a sore throat is investigated at all rather than simply treated: it causes complications of two kinds, one by direct spread from the throat and one through an immune response that appears weeks later. Finding it means deciding which children to test, and the first thing that shapes that decision is the child’s age.
The clinical picture changes with the age of the child
Age does more work in this differential than any individual sign, because it sets the pre-test probability: how likely GAS is before any test has been done. The presentation also changes with age, so the classic picture of streptococcal tonsillitis is a poor guide in the youngest children.
| Age | Typical presentation | What it means for testing |
|---|---|---|
| Under 12 months | Pharyngitis is almost always viral — of the order of 99% of cases; often non-specific fussiness, poor feeding and low-grade fever | The pre-test probability of GAS is low, so a swab is rarely informative; management is usually supportive |
| 1–3 years | Often non-specific: protracted rhinitis and nasal discharge, low-grade fever, irritability, poor appetite, tender anterior cervical nodes — sometimes called streptococcosis — rather than the classic exudative tonsillitis | GAS still occurs and is missed if not tested |
| 3 years and older | Abrupt sore throat, fever, exudative tonsillitis and tender anterior cervical lymphadenopathy; headache, vomiting and abdominal pain are common in children | The age band in which the familiar score-and-swab reasoning applies |
The old rule that children under 3 years are viral by default is no longer used. The only age band in which the pre-test probability is low enough to justify not testing is the first year of life. From the second year onwards, the question becomes whether the examination can identify GAS without a test.
Clinical signs cannot separate GAS from adenovirus or EBV
The widespread assumption that exudate — the coating of inflammatory material over the tonsils — means bacteria does not survive inspection. Studies in the early 1980s showed that adenovirus produces as much tonsillar exudate as GAS, and that the two are indistinguishable at the bedside. EBV produces the heaviest exudate of the three: the membranes can coalesce over both tonsils, the illness is prolonged, and airway compromise is possible.
One sign does discriminate between two membranous causes: what happens when the membrane is peeled away.
| Membrane | Cause | Bleeds when removed? |
|---|---|---|
| Grey-white pseudo-membrane that stays in place | EBV infectious mononucleosis | No |
| Adherent, grey, necrotic membrane with underlying mucosal bleeding | Diphtheria (Corynebacterium diphtheriae) | Yes, because the tissue beneath is necrotic |
The distinction changes management. A child with EBV is uncomfortable and may need airway support, but EBV has no specific antiviral therapy and the illness is expected to resolve. A child with diphtheria is systemically unwell because the toxin can cause myocarditis, and diphtheria kills 5% to 10% of patients even with treatment. Treatment is time-critical because antitoxin neutralises only toxin that is still unbound. Diphtheria remains rare in Western Europe, but it is re-emerging where vaccination coverage has fallen, and cases have been imported into countries with disrupted immunisation programmes.
For everything else, the position is the one the guidelines state directly: because the signs and symptoms of streptococcal pharyngitis overlap extensively with other infections, a diagnosis should not be made on clinical grounds alone. What justifies the effort of establishing the organism is not the sore throat itself but what group A Streptococcus does afterwards, which is the subject of Pediatric Group A Streptococcus: Virulence and Complications.