Contagiousness Duration for Strep Pharyngitis

Strep pharyngitis remains contagious until 24 hours after starting appropriate antibiotic therapy. 1

Contagiousness Timeline

Patients are no longer contagious after completing 24 hours of appropriate antibiotic therapy (penicillin, amoxicillin, or other appropriate antibiotics). 1, 2
Clinical improvement typically occurs within 24-48 hours of starting antibiotics, though this represents symptom relief rather than complete bacterial clearance. 3, 2
The full 10-day antibiotic course must still be completed to maximize bacterial eradication from the pharynx and prevent complications like acute rheumatic fever, even though contagiousness ends much earlier. 3, 4

Untreated strep throat remains contagious for the entire duration of illness and potentially for weeks afterward as a carrier. 1
Strep pharyngitis is a self-limited disease that typically resolves within less than 1 week even without antibiotics, but the patient remains infectious throughout this period. 3

Children with strep pharyngitis should complete a full 24 hours of antibiotics before returning to school or daycare. 5
Research demonstrates that 36% of patients still had positive throat cultures the morning after initiating antibiotic therapy, but 83% became culture-negative within the first 24 hours. 5

Healthcare workers with symptomatic strep pharyngitis must stay away from clinical work until at least 24 hours of appropriate therapy AND resolution of symptoms has occurred. 1
Asymptomatic healthcare workers who test positive should stay away from work until 24 hours of appropriate therapy. 1
A longer exclusion period may be required for healthcare workers with skin lesions or in outbreak situations. 1

Do not confuse the 24-hour contagiousness window with the 10-day treatment duration—both are important for different reasons. 1

24 hours of antibiotics: Eliminates contagiousness and allows return to normal activities. 1, 5
10 days of antibiotics: Required to maximize bacterial eradication and prevent acute rheumatic fever. 3, 4

Asymptomatic carriers can harbor Group A Streptococcus for several months, though they are unlikely to spread the organism to close contacts and are at little or no risk for complications. 1, 6
Chronic GABHS colonization is common despite appropriate antibiotic therapy, but these carriers are at low risk of transmitting disease. 6
Routine testing or empiric treatment of asymptomatic household contacts is not recommended. 3, 1

Up to one-third of households include individuals who will develop symptomatic GAS pharyngitis that warrants diagnostic testing and treatment. 3
Household contacts should only be tested and treated if they develop symptoms consistent with strep pharyngitis. 1
Penicillin prophylaxis has not been shown to reduce the incidence of subsequent GAS pharyngitis in household contacts. 3, 1
Given the self-limited nature of GAS pharyngitis, high frequency of GAS throat carriage, limited efficacy of antibiotic prophylaxis, and potential concerns about antibiotic resistance, routine testing or treatment of asymptomatic household contacts is not warranted. 3

Do not allow patients to return to school/work before completing 24 hours of antibiotics, even if they feel better the morning after starting treatment—research shows over one-third still have positive cultures at that point. 5
Do not discontinue antibiotics after 24 hours when symptoms improve and contagiousness ends—the full 10-day course is essential for preventing rheumatic fever. 3, 4
Do not test or treat asymptomatic household contacts as this has not been shown to be beneficial and contributes to antibiotic resistance. 3, 1