After 24 hours of starting antibiotic treatment. To explain this in detail, let first provide some information about strep and its treatment with antibiotics:

Step 1: Understanding strep throat
Strep throat is an infection caused by group A Streptococcus bacteria. It is a common infection in children and can cause a sore throat, fever, and swollen lymph nodes. If left untreated, it can lead to more serious complications like rheumatic fever or scarlet fever.

Step 2: Treating strep throat with antibiotics
Antibiotics are usually prescribed to treat strep throat. The most commonly used antibiotics include penicillin, amoxicillin, and cephalosporins. These medications work by targeting and killing the bacteria that cause the infection.

Step 3: Time required for strep to become non-contagious after starting antibiotics
It takes approximately 24 hours after starting antibiotic treatment for the patient to become non-contagious. This is because it takes around this amount of time for the antibiotic to reach the appropriate levels in the bloodstream and start effectively killing the bacteria. During this time, it is essential for the infected individual to take the antibiotics as prescribed and to follow proper hygiene practices to avoid spreading the infection to others.

Step 4: How antibiotics work against strep throat
Antibiotics work by inhibiting the bacteria's ability to produce cell walls or by killing the bacteria outright. Once the antibiotics are in the bloodstream, they travel to the throat and inhibit or kill the bacteria. This process helps to eliminate the infection and prevent further spread.

Step 5: Proper hygiene during the contagious period
To reduce the risk of spreading strep throat to others, individuals should practice good hygiene during the contagious period. This includes washing their hands frequently, covering their mouth and nose when coughing or sneezing, and avoiding close contact with others. Additionally, they should not share personal items like toothbrushes or utensils until they have completed the full course of antibiotics.

Step 6: Importance of taking antibiotics as prescribed
To ensure that strep throat is effectively treated and the patient becomes non-contagious within 24 hours of starting antibiotic treatment, it is critical to take the medication as prescribed. Missing doses or stopping the medication early can result in incomplete eradication of the bacteria and prolong the contagious period, which may lead to complications or the possibility of reinfection.

In conclusion, the answer to the question, "when are you not contagious after starting antibiotics for strep?" is after 24 hours of starting antibiotic treatment. This is because it takes this amount of time for the antibiotics to reach effective levels in the bloodstream and kill the bacteria, reducing the likelihood of spreading the infection to others. It is essential to follow proper hygiene practices and take antibiotics as prescribed during this time to prevent complications and reinfection.