How Strep Throat Spreads
Strep throat spreads primarily through respiratory droplets when an infected person coughs or sneezes, requiring close contact with someone who has active symptoms. 1
Primary Transmission Routes
Respiratory droplets are the main mode of transmission. When someone with acute streptococcal pharyngitis coughs or sneezes, they release bacteria-laden droplets into the air that others can inhale during close contact. 1 This makes symptomatic individuals the most contagious, as they actively shed bacteria through their respiratory secretions. 1
Direct contact with infected secretions or contaminated surfaces can also transmit the bacteria, though this is a less common route. 1 While streptococci can survive in dust and on objects (fomites), environmental sources account for only about 10% of transmission cases. 1
Who Is Most Contagious
People with acute pharyngitis symptoms are highly contagious, while asymptomatic carriers pose minimal transmission risk. 1 This is a critical distinction:
- Symptomatic patients actively spread the organism to close contacts 1
- Asymptomatic carriers (up to 20% of school-aged children during winter/spring) are unlikely to spread the organism to their close contacts and pose very low transmission risk 1, 2
- Carriers have bacteria present but show no immunologic response (no rising antibody titers), making them fundamentally different from acutely infected individuals 1, 2
Household and Close Contact Risk
Approximately 25% of household members may harbor the bacteria, but routine testing or treatment of asymptomatic contacts is not necessary except in specific high-risk situations. 3 These exceptions include:
- History of rheumatic fever 1
- Documented outbreak settings 1
- Closed or semi-closed communities experiencing outbreaks 2
The risk of transmission is substantially higher from symptomatic individuals than from carriers. 1 Secondary cases of severe invasive infection have rarely occurred in family contacts. 3, 1
Seasonal and Environmental Factors
Transmission peaks during winter and spring in temperate climates, when up to 20% of asymptomatic school-aged children may be carriers. 1, 2 The bacteria can persist in the environment, but this is not the primary concern for transmission. 1
Common Pitfall to Avoid
Do not confuse an asymptomatic positive throat culture with active contagious infection. 2 Carriers colonized for several months may test positive during intercurrent viral pharyngitis, appearing to have strep throat when they actually have a viral infection and are not spreading streptococcus. 3