How Long Are You Contagious With Strep After Antibiotics?

With strep throat, you are generally considered no longer contagious after 24 hours on appropriate antibiotics, provided you no longer have a fever. Some guidance uses 12 hours. Most schools and workplaces in the US use the 24-hour standard.

Without antibiotics, you can remain contagious for two to three weeks.

Timeline on treatment

Why you must finish the full course

You will feel better in two or three days. The antibiotic course is ten days for penicillin or amoxicillin. Stopping early is the mistake, and the reason is specific to strep.

Strep bacteria can trigger an immune reaction that damages heart valves — rheumatic fever. It develops two to four weeks after the throat infection and is the reason strep is treated with antibiotics at all, given that the sore throat itself would resolve on its own. The full ten-day course is what reliably clears the bacteria and prevents this.

Rheumatic fever is now rare in the US precisely because of this practice. That is not a reason to relax about it.

If you are not improving after 48 hours

Antibiotics for strep work quickly. If you are no better after two full days of treatment, call your doctor. Possible reasons:

• The infection was viral all along and the test was a false positive or was not done
• An abscess has formed beside the tonsil — suspect this with severe one-sided pain, difficulty opening the mouth, and a muffled voice. This needs same-day care
• Resistance or an unusual organism, which is uncommon

Preventing reinfection in the household

Strep spreads readily among household members. Practical steps:

• Replace your toothbrush after 24 hours on antibiotics — and again at the end of the course
• Do not share cups, utensils, towels, or food
• Wash hands frequently
• Household members with symptoms should get tested; those without symptoms generally do not need testing or treatment

What helps the throat pain meanwhile

Antibiotics treat the bacteria, not the pain. For the first 48 hours:

• Ibuprofen tends to work better than acetaminophen for throat pain because of the inflammation involved — see the comparison
• Salt water gargle several times daily
• Cold foods: ice pops, ice cream, cold yogurt
• Warm tea with honey
• Soft foods only — skip anything sharp or acidic

Was it definitely strep?

Only about one in ten adult sore throats is strep. If you were not tested, it may well have been viral, in which case antibiotics were not doing anything. The absence of a cough, plus white patches, swollen tender glands, and fever, is the classic strep picture. Read strep throat versus viral sore throat and, if you had no fever, sore throat with no fever.

Returning to work or school

Standard guidance: 24 hours on antibiotics and fever-free without medication. Most US schools require this. Note that the fever must be gone on its own — see how long you are contagious after a fever breaks.

Get urgent care for

Difficulty breathing or swallowing, drooling, inability to open your mouth fully, severe one-sided throat swelling, a rash, dark urine, or joint pain and swelling in the weeks after the infection.

Related reading

• Acetaminophen vs Ibuprofen for Fever: Which Works Better?
• Strep Throat vs Viral Sore Throat: Key Differences
• Sore Throat but No Fever: What It Actually Means

Sources

• Centers for Disease Control and Prevention
• MedlinePlus — U.S. National Library of Medicine
• Drug Information — MedlinePlus