It is possible to get strep throat again shortly after receiving treatment for a previous infection. Strep throat is caused by the bacterium Streptococcus pyogenes, also known as Group A Streptococcus (GAS). This bacterium is successfully treated with antibiotics, but recovery does not guarantee lasting protection against future infections. Symptoms returning soon after finishing medication are a concern regarding re-infection or recurrence.
Understanding Strep Strains and Immunity
Immunity to Group A Streptococcus is highly specific and does not provide blanket protection against all variations of the bacteria. The immune system primarily targets a surface protein on the bacteria called the M-protein, which is a major virulence factor. The gene that encodes this M-protein, the emm gene, is highly variable, leading to the existence of over 200 distinct serotypes, or strains, of GAS.
When a person recovers from a strep infection, their body develops protective antibodies directed specifically against the M-protein of the infecting strain. This means that immunity is serotype-specific; the person is protected from that particular strain, but remains susceptible to any of the other circulating serotypes. The existence of numerous strains makes it possible to contract a new infection quickly, even after the previous one was fully cleared.
Contracting an infection from one serotype, such as emm1, grants protection against only that strain. However, the body remains vulnerable to subsequent infections from other serotypes, like emm28 or emm89. Constant exposure to various strains, especially in high-contact environments like schools, increases the likelihood of sequential infections.
Is It New Strep or a Lingering Infection?
When strep symptoms return soon after antibiotic treatment, doctors must determine if it is a true re-infection or a recurrence, as the distinction affects management. A true re-infection means the patient has been exposed to and contracted a completely new strain of Group A Streptococcus. This is generally treated as a new, separate infection with a standard course of antibiotics.
The second possibility is a recurrence, meaning the original infection was not completely eradicated. This happens if the prescribed course of antibiotics was not fully completed, allowing some bacteria to survive and multiply once the medication stops. Studies have shown that patients often stop taking their medication early once symptoms improve, which fosters recurrence.
A common scenario leading to a positive test after treatment is the patient being an asymptomatic carrier, or colonized, with GAS. Carriers harbor the bacteria in their throat without experiencing typical strep throat symptoms. While carriers are generally less contagious than those with an active infection, they can still test positive for the bacteria.
In this situation, the patient’s current symptoms may be caused by a viral illness, with the positive strep test resulting only from the carrier state. Treating the carrier state is often unnecessary unless complications are present or there is an outbreak. Distinguishing between a true recurrent infection and the carrier state can involve a follow-up culture after antibiotic treatment or checking for specific antibodies.
Preventing Future Strep Infections
Protecting against future strep infections involves hygiene practices to minimize exposure to the bacteria. Since the bacteria spread through respiratory droplets from coughing or sneezing, frequent and thorough hand washing is a primary defense. Hands should be washed with soap and water for at least 20 seconds, especially after coughing or being in public.
It is important to avoid sharing personal items that come into contact with the mouth or nose, such as utensils or towels. The strep bacteria can live on these surfaces, facilitating transmission from an infected person or a carrier. After completing the antibiotic course, replacing the toothbrush is recommended to prevent re-infection from residual bacteria on the bristles.
People with repeated infections should ensure that close contacts, particularly family members, are tested if they develop symptoms. This helps identify and treat the source of potential re-exposure, which is often an asymptomatic carrier in the household. Completing the entire course of antibiotics as prescribed, even after symptoms disappear, is necessary to ensure the initial bacterial population is fully eliminated, reducing the risk of recurrence.