How Strep Throat Spreads
Strep throat spreads primarily through respiratory droplets released when an infected person coughs, sneezes, talks, or sings, with transmission occurring mainly during close contact with symptomatic individuals. 1
Primary Transmission Routes
Respiratory droplets are the dominant mechanism of spread. When someone with strep throat coughs or sneezes, they expel bacteria-containing droplets into the air that can be inhaled by people in close proximity (typically within 1 meter). 1, 2 The droplets produced during talking and coughing average 50-100 micrometers in size, with considerable variation between individuals. 3
Direct contact with infected secretions also transmits the bacteria. This occurs when:
- An infected person coughs or sneezes into their hand, then shakes hands with another person 4
- Someone touches contaminated surfaces (fomites) and then touches their nose, mouth, or eyes 4, 1
- Direct contact occurs with tissues or other items recently contaminated with respiratory secretions 4
Contagiousness Timeline and Risk Factors
The incubation period is 2-5 days after exposure. 2 People with acute pharyngitis are most contagious when symptomatic, actively shedding bacteria through respiratory secretions. 1 After starting appropriate antibiotic therapy, patients become non-contagious within 24 hours. 5
Symptomatic individuals pose the highest transmission risk. Acute pharyngitis patients are the primary source of spread, while asymptomatic carriers (less than 5% of adults) are unlikely to transmit the organism to close contacts and pose very low risk. 1 During winter and spring, up to 20% of school-aged children may be asymptomatic carriers, but these carriers rarely transmit infection. 1, 2
Environmental and Seasonal Factors
Strep throat peaks in late winter and early spring when children are predominantly indoors for school and sports, facilitating close contact transmission. 2 While streptococci can survive in dust and on fomites, this is not the primary transmission route—environmental sources account for only 9.8% of cases in outbreak investigations. 1
The disease is most common in school-aged children with a peak at 7-8 years of age, and is rare in children under 3 years old. 2 In crowded settings like schools, outbreaks are common due to increased opportunities for respiratory droplet transmission. 2
Household Transmission Risk
Household contacts do not routinely require testing or treatment except in specific high-risk situations (history of rheumatic fever, outbreak settings, or frequent infections). 1 The risk of transmission to close contacts is substantially higher from symptomatic individuals than from carriers. 1 Secondary cases of severe invasive strep infection have rarely occurred in family contacts. 1
Key Clinical Pitfall
Do not confuse asymptomatic carriers with infectious cases. Carriers have bacteria present but show no immunologic response (no rising antibody titers) and pose minimal transmission risk. 1 Routine screening and treatment of asymptomatic household contacts is not recommended in typical circumstances. 1