Tonsillitis and strep throat: how to tell viral from bacterial, and when antibiotics really matter

Is my sore throat viral or bacterial?

Most likely viral. The large majority of sore throats, including most cases of tonsillitis, are caused by the same viruses that cause colds and flu. They usually come with a cough, a runny nose, a hoarse voice or red eyes, and they settle on their own within about a week. Antibiotics do nothing for them. The bacterial infection doctors watch for is strep throat, caused by group A streptococcus, a bacterium also known as Streptococcus pyogenes. It is most common in children and teenagers between about 5 and 15 years old, and it is much less common in adults.

Tonsillitis simply means inflamed tonsils, the two pads of tissue at the back of the throat. It is a description, not a cause, and both viruses and bacteria can produce it. Red, swollen tonsils with white spots look alarming, but they can be caused by a virus too, including the virus behind glandular fever. That is why the appearance of the throat alone is not enough to decide on antibiotics.

A 2023 study in Dammam, in Saudi Arabia's Eastern Province, gives a sense of the real numbers. Doctors performed a rapid strep test on 469 children and adults who came to primary health centres or a children's emergency department with respiratory symptoms. Only 4.1% tested positive overall. In the primary health centres just 0.6% were positive, compared with 14% of the children seen in the emergency department. In other words, most people who walk into a clinic with a sore throat do not have strep.

Signs that point to strep throat: the Centor and FeverPAIN scores

Doctors use simple scoring systems to estimate how likely a sore throat is to be strep. The best known is the Centor score, which gives one point each for a fever above 38 degrees Celsius, the absence of a cough, swollen and tender glands at the front of the neck, and swelling or pus on the tonsils. A modified version, called the McIsaac score, adds a point for children aged 3 to 14 and takes one away for adults over 45. The FeverPAIN score, used widely in the UK, counts fever in the past day, pus on the tonsils, coming to the doctor within three days of starting, very inflamed tonsils, and no cough or runny nose.

A low score makes strep unlikely, and most guidelines say no antibiotic and no test is needed. A higher score raises the probability, but even a high score is wrong a good part of the time. In the Dammam study, patients with the maximum score of 5 had the highest positive rate, yet only 33.3% of them actually had strep on the rapid test. The authors concluded that a Centor score of 2 or more should be followed by a confirmatory test rather than an automatic antibiotic.

Some clues point the other way, towards a virus. A cough, a runny or blocked nose, hoarseness, red itchy eyes, mouth ulcers or diarrhoea all make strep less likely. A sore throat that comes with a fine, rough red rash that feels like sandpaper, often on the neck and chest, can be scarlet fever, which is strep with a rash and does need a doctor.

The rapid strep test and throat swab: what to expect

The rapid antigen detection test, often called the rapid strep test, looks for proteins from group A streptococcus on a swab taken from the back of the throat. The swab takes a few seconds and can make you gag briefly, but it is not painful. The result is usually ready in 10 to 15 minutes, while you are still in the clinic. When the test is positive, it is very reliable, and the Dammam researchers highlighted its high specificity as a way to avoid prescribing antibiotics that are not needed.

A negative rapid test in an adult with a typical viral picture is usually enough to stop there. In children, some doctors send a second swab for a throat culture, which is grown in the laboratory for a day or two, because the rapid test can occasionally miss strep. If your clinic does not have rapid tests, ask whether a throat culture can be sent to a laboratory. Waiting a day or two for a result is safe for most people, because a short delay in starting treatment does not remove the protection against rheumatic fever.

Do not take an antibiotic you already have at home before the swab. Even one or two doses can make the test falsely negative, which leaves you and your doctor guessing. If you have already started one, tell the doctor what you took and when.

Why antibiotics are bought for nearly every sore throat, and why it backfires

Across much of the region, a sore throat and an antibiotic go together. The antibiotic can be bought over the counter, the pharmacist is the first and sometimes the only health worker a family sees, and there is a widespread belief that tonsillitis always needs one. Researchers measured this in 2025 in Port Sudan. A trained simulated patient visited 113 community pharmacies describing an acute sore throat. An antibiotic was dispensed without a prescription in 80.5% of visits, and azithromycin made up 76.1% of the antibiotics handed over.

Doctors' prescriptions follow a similar pattern. A review of prescriptions for employees in Greater Beirut found that 94.6% of adults diagnosed with acute pharyngitis, an inflamed throat, were given an antibiotic, and about a third of those were broad-spectrum third-generation cephalosporins or fluoroquinolones, which are not first-line choices for a sore throat.

This matters for three reasons. A viral sore throat gets no benefit, while the antibiotic can still cause diarrhoea, rashes and allergic reactions. Overuse breeds resistant bacteria, and azithromycin in particular loses its power against strep when it is used heavily. And antibiotics taken for a few days and then stopped, which is common when bought without advice, may calm the symptoms of a real strep infection without clearing the bacteria. Penicillin and amoxicillin remain the standard first choice for confirmed strep, because group A streptococcus has not become resistant to penicillin.

When strep is confirmed: why the full course matters

If a test confirms strep, antibiotics are genuinely useful. They shorten the illness by a day or so, reduce the chance of passing the infection to others, lower the risk of complications such as a tonsil abscess, and above all prevent rheumatic fever. The usual first choice is penicillin V or amoxicillin by mouth. Many guidelines advise a course of about ten days for strep throat, and the length your doctor prescribes is the length to take. For people allergic to penicillin, the doctor will choose an alternative.

The temptation is to stop once the throat feels better, often after two or three days. That is exactly when the bacteria may still be present in the tonsils. A course cut short is one of the reasons strep can return, and in places where rheumatic fever still occurs, incomplete treatment removes the protection the antibiotic was meant to give. If side effects make it hard to keep going, speak to the doctor or pharmacist rather than simply stopping.

People with strep throat stop being infectious to others after about 24 hours of the right antibiotic. A child can usually go back to school after a full day of treatment once the fever has gone. Family members who develop a sore throat in the following days should be checked rather than given leftover tablets.

Rheumatic fever and rheumatic heart disease: why strep is taken seriously

In a small number of people, usually children, an untreated strep throat is followed two to four weeks later by rheumatic fever. This is not an infection of the heart but an immune reaction: the body's defences, primed against the streptococcus, attack its own tissues. It can cause fever, painful swollen joints that move from one joint to another, a rash, jerky involuntary movements, and inflammation of the heart. Repeated attacks scar the heart valves, a condition called rheumatic heart disease, which can lead to heart failure, stroke and the need for valve surgery in young adults.

According to the World Health Organization, rheumatic heart disease is the most common acquired heart disease in people under 25. It affects an estimated 55 million people worldwide and causes around 360,000 deaths a year, the large majority in low and middle income countries. It has largely disappeared from wealthy countries, but it has not disappeared from this region.

In Egypt, a 2023 study screened 1,560 school children aged 6 to 18 in the eastern governorates with heart ultrasound and found definite rheumatic heart disease in 2.3% of them, with leaking of the mitral valve the most common finding. In Sudan, rheumatic heart disease is the leading cause of acquired heart disease in children and young adults, and the Federal Ministry of Health, working with the WHO regional office, issued simplified national guidelines in 2023. They advise primary care workers to treat a sore throat without viral symptoms in school-age children as bacterial, and to start preventive penicillin as soon as rheumatic fever is suspected.

Anyone who has had rheumatic fever usually needs regular preventive penicillin injections for years to stop further attacks. If your child develops joint pain, breathlessness or unusual movements a few weeks after a sore throat, tell the doctor about the throat infection, because that detail can change the diagnosis.

How to ease a sore throat at home

Whether the cause is a virus or strep, the same home measures help with the pain. Drink plenty, even when swallowing hurts, because dehydration makes everything feel worse. Cool drinks and soft foods such as yoghurt, soup and ice lollies are often easier than hot, spicy or crunchy foods. Paracetamol or ibuprofen, used as the pack directs, relieve the pain and fever and make it easier to eat and drink.

Gargling with warm salty water can soothe the throat in adults and older children who can gargle without swallowing. Warm drinks with honey and lemon help many people, but honey should never be given to babies under one year old. Medicated lozenges and throat sprays can numb the throat for a while, though they are not suitable for young children.

Most viral sore throats improve within three to seven days. See a doctor if the pain is getting worse after three or four days, if the fever is high and persistent, if the sore throat keeps coming back, or if you have a weakened immune system. People taking medicines that lower white blood cells, such as some thyroid, rheumatology and cancer treatments, should get a sore throat with fever checked quickly.

Danger signs: quinsy and other throat emergencies

Occasionally tonsillitis leads to a collection of pus beside the tonsil, called a peritonsillar abscess or quinsy. It usually affects one side only. The pain becomes severe and one-sided, swallowing even saliva becomes difficult, the voice sounds muffled as if speaking with a hot potato in the mouth, and it may be hard to open the mouth fully. Quinsy needs hospital treatment, usually draining the pus and antibiotics, and it will not settle with tablets at home.

Other serious throat infections can spread into the deep tissues of the neck or swell the airway itself. In a child, drooling, leaning forward to breathe, a high-pitched noise when breathing in, or refusing to swallow are warning signs that need emergency care immediately. Do not try to look into the throat of a child who is struggling to breathe, as this can make it worse. Keep the child calm and upright and get to hospital.

Severe dehydration, a stiff neck with fever, and a rash that does not fade when pressed are also reasons to seek urgent help, because they can point to an infection beyond the throat.

When is tonsillectomy considered?

Removing the tonsils, called tonsillectomy, used to be offered very readily, and many parents in the region still hear it suggested after two or three bad episodes. Current evidence supports a more selective approach. A 2023 systematic review and international consensus on recurrent tonsillitis concluded that surgery is highly effective for people who have had seven or more properly treated episodes in the past year, five or more in each of the past two years, or three or more in each of the past three years.

The same review recommends counting episodes carefully and recording how much each one affects daily life, school or work, because memory tends to exaggerate. Other reasons doctors consider surgery include repeated quinsy and, in children, tonsils so large that they block breathing at night, causing loud snoring with pauses in breathing, restless sleep and daytime tiredness.

Tonsillectomy is a common operation, but it is not trivial. Pain after surgery is significant for a week or more, and there is a small risk of bleeding in the days that follow, which is a reason to stay near a hospital during recovery. Many children have fewer throat infections as they grow older even without surgery, so a period of careful observation is often reasonable.

Sources

• World Health Organization: Rheumatic heart disease fact sheet
• Al-Baghli NA, Al Saif A, Al Dorazi SA et al: Prevalence of Positive Rapid Antigen Detection Test for Group A Streptococcus Among Patients With Respiratory Symptoms in Eastern Province, Kingdom of Saudi Arabia, Cureus, 2023
• Fareed A, Saleh O, Maklady F et al: Screening for the prevalence of rheumatic heart disease among school children in Egypt, Echocardiography (Mount Kisco, N.Y.), 2023
• Ali Sulafa KM, Karrar ZA, Elkurdufani N et al: Sudan's rheumatic fever and rheumatic heart disease guidelines: a simplified approach in an endemic country, Frontiers in cardiovascular medicine, 2024
• Hamadouk RM, Ibrahim OM, Ahmed MT et al: Non-Prescription Dispensing of Antibiotics in Community Pharmacies in Port Sudan: A Simulated Patient Study Using a Sore Throat Scenario in a Conflict-Affected Setting, Integrated pharmacy research & practice, 2026
• Lakkis NA, Alameddine R, Issa HG et al: Prescribing antibiotics in adults with respiratory tract infections in Lebanon, International journal of clinical practice, 2021
• Guntinas-Lichius O, Geißler K, Mäkitie AA et al: Treatment of recurrent acute tonsillitis-a systematic review and clinical practice recommendations, Frontiers in surgery, 2023