Tonsillitis: sore throat, virus or bacteria, and when antibiotics help
In winter, sore throat is one of the most common reasons adults and children see a doctor. This guide explains tonsillitis, how a doctor tells a virus from bacteria, when an antibiotic makes sense, the warning signs and what a video consultation can do for you.
Tonsillitis is acute inflammation of the tonsils and, in most cases, it is caused by a virus and clears up without an antibiotic. When the cause is a bacterium, almost always group A streptococcus, an antibiotic helps recovery and prevents complications. To decide, the doctor assesses fever, cough, neck glands and the appearance of the tonsils and, when justified, requests a rapid test. Difficulty opening the mouth, swallowing saliva or breathing are warning signs.
Definition
What acute tonsillitis is
Acute tonsillitis is an acute inflammation of the tonsils, the two masses of defensive tissue you can see at the back of the throat, one on each side.
The inflammation often spreads to the rest of the pharynx. For this reason, the Portuguese Directorate-General of Health (DGS) treats the terms acute tonsillitis, acute pharyngitis and acute tonsilitis as equivalent. In everyday language people simply speak of an “inflamed throat”.
Most cases of tonsillitis are caused by a virus, are harmless and clear up on their own. Among bacteria, the most common cause is group A Streptococcus, also called group A beta-haemolytic streptococcus. This is mainly the case that justifies an antibiotic.
Source: DGS — Norma n.º 020/2012, Diagnosis and Treatment of Acute Tonsillitis in Children.
How it shows
Sore throat and other symptoms of tonsillitis
The main symptom is a sore throat that gets worse when swallowing and usually starts suddenly.
- Sore throat and pain on swallowing.
- Fever, sometimes above 38 °C.
- Red, enlarged tonsils, with or without whitish patches (exudate).
- Swollen neck glands that are tender to the touch.
- Headache and feeling unwell.
- In children, also vomiting and stomach ache.
White patches on the tonsils look alarming, but they do not prove that the cause is bacterial: they also appear in viral infections. No single symptom is enough to confirm or rule out streptococcus.
The main question
Viral or bacterial tonsillitis: how to tell them apart
The difference matters because an antibiotic only helps when the cause is bacterial.
| More in favour of a virus | More in favour of streptococcus |
|---|---|
| Cough, runny nose, hoarseness | Sudden onset with severe sore throat |
| Conjunctivitis, mouth ulcers or sores | High fever, no cough |
| Diarrhoea | Tender neck glands |
| No fever | Small red spots on the roof of the mouth or a skin rash typical of scarlet fever |
According to the DGS guideline, cough, runny nose, hoarseness, conjunctivitis, mouth ulcers or diarrhoea strongly suggest viral tonsillitis. In children, group A streptococcus is responsible for about 37 % of acute tonsillitis.
Source: DGS — Norma n.º 020/2012.
Centor and McIsaac
The criteria the doctor uses to decide
In adults and adolescents, doctors often use a simple score, the Centor score, or its age-adjusted version, the McIsaac score.
- 1 point if you have had a fever.
- 1 point if you have no cough.
- 1 point if you have patches (exudate) on the tonsils.
- 1 point if you have swollen glands at the front of the neck.
- McIsaac adjustment: add 1 point under the age of 15 and subtract 1 point from the age of 45.
In a study of more than 206 000 people with a sore throat, among patients aged 15 or over the streptococcus test was positive in 7 % of those with 0 points and in 57 % of those with 4 points. In other words: with few points, the probability of bacteria is low; with many points, it needs to be confirmed.
In the original study by McIsaac and colleagues, following this score would have reduced initial antibiotic prescriptions by 48 %, without increasing the number of throat swabs.
Sources: Fine AM et al., Archives of Internal Medicine 2012;172(11):847-852; McIsaac WJ et al., CMAJ 1998;158(1):75-83.
Paediatric age
Tonsillitis in children
Streptococcal tonsillitis is most common at school age, between 5 and 15 years, with peaks in winter and early spring.
- Before the age of 3, streptococcal tonsillitis is rare and the DGS does not recommend routine testing, unless there has been close contact with a confirmed case.
- In older children and adolescents with suggestive signs, the DGS recommends confirming streptococcus with a rapid antigen test or a throat culture before starting an antibiotic.
- If the rapid test is positive, it does not need confirmation: it is considered diagnostic.
- Spread at home: in 43 % of families with one case of streptococcal tonsillitis, a second case appears. The incubation period is 2 to 5 days.
- Siblings without symptoms need neither a test nor treatment.
Source: DGS — Norma n.º 020/2012.
Treatment
Tonsillitis: when an antibiotic helps and when it does not
In viral tonsillitis, an antibiotic does not speed up recovery and exposes you to side effects and resistance. In confirmed streptococcal tonsillitis, treatment is recommended.
A Cochrane review of 29 trials, with more than 15 000 cases of sore throat, showed that 82 % of people without an antibiotic no longer had symptoms after one week. The antibiotic reduced sore throat and headache on the third day and reduced complications such as ear infection and peritonsillar abscess, which were nevertheless uncommon.
In children and adolescents with confirmed streptococcal tonsillitis, the DGS guideline considers an antibiotic mandatory. Amoxicillin is the first choice, usually for 10 days. The doctor adjusts the treatment if there is a penicillin allergy.
Why to be careful with antibiotics: mononucleosis
Infectious mononucleosis, caused by the Epstein-Barr virus, can look like tonsillitis: fever, severe sore throat, swollen tonsils, sometimes with patches, and enlarged neck glands. It is a viral infection, so an antibiotic does not help. If amoxicillin is given to a person with mononucleosis, a skin rash often appears, which can be severe, and the person may be labelled as allergic to penicillin for years. For this reason, the doctor should confirm the cause before prescribing an antibiotic, and you should never take antibiotics you have left over at home.
- Spread: after 24 hours of antibiotic, transmission is practically nil.
- Waiting for the test is safe: delaying the start of the antibiotic until the 9th day of illness does not increase the risk of rheumatic fever, so in doubtful cases the result can be awaited.
- Finish the treatment, even if the pain goes away after two or three days.
Sources: Spinks A, Glasziou PP, Del Mar CB, Cochrane Database Syst Rev 2021;12:CD000023; DGS — Norma n.º 020/2012.
Care
How to relieve a sore throat at home
Whether viral or bacterial, tonsillitis is also treated by relieving pain and fever.
- Paracetamol or ibuprofen relieve pain and fever, in adults and children, whatever the cause. Follow the dose indicated for weight and age, and ask the doctor if you have chronic conditions, are pregnant or take other medicines.
- Frequent drinks, warm or cold, in small sips.
- Soft foods while swallowing hurts.
- Rest and fresh air in the house.
- Wash your hands and do not share glasses or cutlery.
If the sore throat does not improve after a few days, gets worse after starting to improve, or if tonsillitis recurs several times a year, speak to a doctor.
Source: DGS — Norma n.º 020/2012.
When it is urgent
Warning signs and peritonsillar abscess
The best-known local complication of tonsillitis is the peritonsillar abscess: a collection of pus next to one of the tonsils, more common in adolescents and young adults.
The abscess needs to be drained by a doctor and treated with an antibiotic. For this reason, a very severe sore throat on one side only, which gets worse instead of better, should not wait.
Sources: MSD Manual — Tonsillar cellulitis and abscess; DGS — Norma n.º 020/2012.
Festive season
Sore throat during the holidays, at school and when travelling
December brings school-age children, grandparents and cousins together in the same house, at the peak of winter when streptococcal tonsillitis is most common.
- Before the family dinner, a child with fever and a severe sore throat should be assessed: if it is streptococcus, they stop being contagious 24 hours after starting the antibiotic.
- Do not share glasses, cutlery or bottles at the table.
- If you are travelling with a sore throat and fever, arrange to be assessed before you leave.
- If you fall ill away from home, a video call lets you speak to a doctor in Portuguese from wherever you are.
Video consultation
How our online consultation helps with tonsillitis
Sore throat is one of the reasons for consultation our video medical consultation was designed for. You can book for the same day, without weeks of waiting.
- Assessment: the doctor asks about fever, cough, how long the symptoms have lasted, contact with cases of tonsillitis and drug allergies.
- Observation by camera: with good light, the doctor can see the tonsils and ask you to point out the neck glands.
- Warning signs: the doctor identifies what needs urgent examination and tells you clearly.
- Tests: when justified, the doctor refers you for a rapid test or throat culture, or for blood tests.
- Clinical plan and medical certificate: you receive a plan at the end of the consultation; a medical certificate can be issued when clinically indicated.
- Referral: if tonsillitis keeps recurring, our doctor refers you to an ear, nose and throat (ENT) specialist.
The consultation lasts 15 minutes, costs €39 and is carried out by a doctor registered with the Portuguese Medical Association (Ordem dos Médicos). Some cases need an in-person examination of the throat; when that is so, the doctor says so clearly and indicates the next step. Book your online medical consultation here.
Care in Portugal
Talk to a doctor about your sore throat
A video consultation lets a doctor assess your throat, rule out warning signs and decide whether a test is needed.
Sore throat and fever?
Talk to a doctor by video call today about your symptoms, the warning signs and whether you need a test.
Sources
Sources for this article
Sources checked on 8 November 2026.
The article explains tonsillitis, the difference between viral and bacterial causes, the warning signs and the treatment options. It does not give medicine doses; that decision rests with the doctor, after assessing each case.
Questions
Frequently asked questions about tonsillitis
Does tonsillitis always need an antibiotic?
No. Most tonsillitis is viral and clears up without an antibiotic. An antibiotic is indicated when the doctor confirms, or considers very likely, a group A streptococcus infection.
Is tonsillitis contagious?
Yes. It spreads through droplets from coughing, sneezing and saliva. In streptococcal tonsillitis, transmission becomes practically nil 24 hours after starting the antibiotic.
How long does a sore throat last?
In most cases it improves within a few days. In a set of clinical trials, 82 % of people without an antibiotic no longer had symptoms after one week. If it gets worse or does not improve, speak to a doctor.
Do white patches on the tonsils mean it is bacterial?
Not necessarily. Patches also appear in viral infections. The doctor combines several signs, such as fever, absence of cough and tender glands, and may request a rapid test.
Can tonsillitis be assessed by video call?
Often, yes. The doctor assesses the symptoms, looks at the throat by camera and decides whether a test or an in-person examination is needed. Shortness of breath, difficulty swallowing saliva or opening the mouth need immediate help.
