How long are strep throat and scarlet fever contagious?

Without antibiotics you can spread it for two to three weeks after symptoms start. Strep throat is caused by the same bacterium and follows the same rule.

This is the one illness on this site that antibiotics change. Scarlet fever, strep throat and tonsillitis caused by group A streptococcus all respond to them, and the contagious period collapses from weeks to a day. That is why the return-to-school rule counts from the first dose rather than from symptoms. It is also why the countries that disagree, France and Italy at 48 hours, the Netherlands with no exclusion at all, are all arguing about the same thing: how wide a safety margin to draw around that first dose.

Day by day

Counting the day symptoms start as day 0, this is how the UK & USA (NHS / CDC) figures fall.

Are you contagious before scarlet fever symptoms start?

The NHS does not say. Its scarlet fever page counts contagiousness from symptoms, two to three weeks without antibiotics, and publishes no incubation period and no pre-symptom figure. The CDC does give an incubation period: it usually takes two to five days after exposure to become ill with strep throat, and the same two to five days for scarlet fever. Neither authority states that you are contagious during those days.

European authorities give different incubation ranges for the same bacterium: Germany's RKI one to three days, France's Ameli one to four, the Dutch RIVM two to five, Spain's Catalan health service three to five. None publishes a pre-symptom contagious figure. What the CDC does say is that if someone has strep throat, the bacteria often spread to other people in their household.

When is scarlet fever most contagious? Before the first dose

For a bacterial infection the most contagious period is simply the untreated period. The NHS says you can spread scarlet fever to other people until 24 hours after you take your first dose of antibiotics; before that dose, while you have the sore throat, fever and rash, you are at your most infectious. Neither the NHS nor the CDC names a peak day within the illness.

It spreads the same way as a cold: the NHS says strep A infections pass by close contact, through coughs and sneezes, or from a wound. Scarlet fever mostly affects young children, according to the NHS, and the CDC says strep throat and scarlet fever are most common in children aged 5 to 15.

How long does scarlet fever last, and when does it stop being contagious?

Scarlet fever lasts for around one week, the NHS says, and a sore throat normally gets better by itself within a week. The contagious period ends much sooner once treatment starts: 24 hours after the first dose of antibiotics, according to the NHS. So for most children the rash and the sore throat are still there on the day they stop being infectious.

Without antibiotics the picture reverses. The NHS says you can spread the infection for two to three weeks after symptoms start, which is longer than the illness itself. Germany's RKI puts the untreated period at up to three weeks, the RIVM at two to three weeks, and Ameli at ten days and up to three weeks. The lesson is the opposite of the one for a cold: with strep, feeling better is not what ends the contagious period; the first dose is.

A peeling rash after scarlet fever, or a throat that is still scratchy on day five, does not mean you are still infectious once you are past the 24 hours. The NHS advice is to keep taking the antibiotics until they are finished, even if you feel better.

The throat swab: what a strep test tells you

A rapid strep test is a throat swab that gives a quick answer on whether group A strep is the likely cause, the CDC says. A throat culture takes longer, because the laboratory waits to see whether the bacteria grow from the swab, and it sometimes finds infections the rapid test misses; the CDC says culture is important after a negative rapid test in children and teenagers.

A positive swab does not settle everything. The CDC explains that a carrier is someone who tests positive but has no symptoms; carriers do not need antibiotics and are less likely to spread the bacteria to others. If a carrier catches a viral sore throat, the strep test can be positive and it is hard to know what is causing the symptoms. In England the NHS says a pharmacist can give the same antibiotic treatment as a GP for a sore throat if you need it.

Antibiotics: what they change, and what they do not

What antibiotics change most is the contagious period, not the length of the illness. The NHS says you stop being able to spread scarlet fever 24 hours after the first dose, and the CDC's clinical guidance says treatment with an appropriate antibiotic for 12 hours or longer limits a person's ability to transmit group A strep. The antibiotic of choice, the CDC says, is penicillin or amoxicillin. The CDC also says antibiotics help people feel better faster and help prevent complications such as rheumatic fever.

They do not, however, end the illness on day one: the rash and sore throat can take about a week to clear. Two rules follow. Finish the course even once you feel better, as the NHS says. And if you have not started antibiotics, the two-to-three-week untreated window applies, which is why the NHS treats scarlet fever as an illness to see a doctor about rather than wait out.

When can you go back to school, nursery or work after scarlet fever or strep throat?

The NHS rule: stay away from nursery, school or work for 24 hours after you take the first dose of antibiotics. The UK Health Security Agency's exclusion list for nurseries and schools uses the same clock: away until 24 hours after antibiotic treatment started. The NHS strep A page repeats it for all group A strep infections, and the NHS wording adds no fever condition.

The CDC draws the line earlier. Its clinical guidance says people can return to work, school or childcare once they have no fever and have had at least 12 to 24 hours of appropriate antibiotics. Germany's RKI and Spain's Catalan service say 24 hours, with the RKI adding that symptoms should be improving and the Catalan rule that the fever should be gone. France's Ameli says 48 hours, and Italy's rule, which comes from a 1998 Ministry of Health circular, is also 48 hours.

The Netherlands stands apart. The RIVM applies no exclusion to an ordinary case of scarlet fever or strep throat: a child can attend school with normal hygiene. The 24-hour rule applies there only to people who work in perinatal care (around births and newborns) or in food preparation, or during an outbreak.

Everyday situations: a newborn, grandparents, a shared bed, the gym, a flight

Count from the first dose of antibiotics. Before it, treat the case as contagious; after 24 hours, the NHS says the risk to others has passed.

• A newborn or a pregnant partner at home: the RIVM singles out perinatal care as the setting where its 24-hour rule always applies, which is a fair signal for a household with a newborn. Keep the sick child away from the baby until 24 hours after the first dose, and do not share towels or bedding, as the NHS advises.
• Grandparents: adults can catch it, though scarlet fever is less common in adults, according to the NHS. Put the visit off until 24 hours after the first dose, and longer if the grandparent has a weakened immune system, which the NHS lists as a reason for urgent advice if they fall ill.
• Sharing a bed: the NHS says do not share cutlery, cups, towels, clothes, bedding or baths with anyone else while contagious. A separate bed for the night before and the night after the first dose is enough on the NHS timeline.
• The gym: strep A spreads by close contact and by coughs and sneezes, the NHS notes. Inside the 24 hours, stay at home; after them, the NHS rule places no restriction.
• A flight or a family dinner: no NHS or CDC rule mentions travel. The 24 hours after the first dose is the NHS threshold; a dinner the evening after the first morning dose falls inside it.
• A care-home visit: neither the NHS nor the UKHSA sets a visitor rule for scarlet fever. Apply the 24-hour rule, and allow the 48 hours that France and Italy use if the person you are visiting is frail.

How long is scarlet fever contagious in children, adults and people with weakened immunity?

Neither the NHS nor the CDC publishes a longer contagious period for any group: the 24-hour rule after the first dose is the same for a five-year-old and an adult, and no European authority in this comparison says otherwise. Children account for most of the cases, not for a longer timeline. The NHS says scarlet fever mostly affects young children and is less common in adults, and the CDC says strep throat and scarlet fever are most common in children aged 5 to 15.

Vulnerability matters for how ill someone gets, not for how long they spread it. The NHS asks for urgent advice if someone with a sore throat has a weakened immune system, for example from diabetes or chemotherapy, has a very high temperature or signs of dehydration, or if the sore throat does not improve after a week. Group A strep can also cause invasive group A strep infection, the NHS says, which is the reason to treat the infection rather than let the three weeks run.

Why the school rule is 24 hours in some countries and 48 in others

Few illnesses show the disagreement so clearly, because here it is entirely about the rule, not the biology. Everyone accepts that antibiotics end contagiousness within a day or two: the NHS says 24 hours, the CDC's clinical guidance says 12 hours or longer limits transmission, the RKI 24 hours, Ameli 48. Those are different safety margins drawn around the same fact.

The UK, Germany, Spain and now the US sit at the short end, 12 to 24 hours after the first dose. France and Italy hold 48 hours, and Italy's rule dates from a 1998 circular that schools and doctors may no longer apply in full. The Netherlands has concluded that excluding an ordinary case is not worth the disruption, and reserves its 24 hours for perinatal care, food preparation and outbreaks.

The untreated figures line up better than the rules: two to three weeks from the NHS and the RIVM, up to three weeks from the RKI, ten days to three weeks from Ameli. If you are in the UK the NHS 24 hours is the rule, and the 48 hours of France and Italy is a reasonable extra margin around a newborn or a frail relative.

What the guidance says in six countries

The same illness, six official positions. Where a country publishes nothing, the table says so rather than borrowing a neighbour's number.

How to stop scarlet fever and strep throat spreading at home

• Start the antibiotics and finish the course, the NHS says; the first dose is what ends the contagious period, and stopping early is what lets the infection come back.
• Keep the sick person away from nursery, school or work for 24 hours after the first dose, as the NHS and the UKHSA advise.
• Wash your hands often with soap and water; both the NHS and the CDC put this first.
• Use tissues to trap germs from coughs or sneezes and bin them straight away, the NHS says.
• Do not share cutlery, cups, towels, clothes, bedding or baths with anyone else; that is also on the NHS list.
• Watch the rest of the household: the CDC says the bacteria often spread to other people in the home, so a second sore throat should be seen and swabbed rather than waited out.

Questions people ask

About this page

Other illnesses

Contagious periods for the other illnesses covered by this tool.

This tool gives general information based on published guidance. It does not diagnose you and does not replace advice from a doctor who knows your situation. You choose the illness; we do not work out what you have.