Nearly everyone has heard of strep throat and the bacteria that causes it—streptococci. But did you know that there are different types of streptococci bacteria, or they can cause other types of infection too? Group C is one of the more elusive forms of streptococci and among two strains we know little about.
In this post, we'll explain what you need to know about group C streptococci.
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Streptococcus¹ is an entire class of organisms. Many of these bacteria play an important role in both animals and humans. Several of them, however, cause illnesses that need medical treatment. The most well-known of these medically significant groups of streptococci are groups A, B, and D, with groups C and G causing less common illnesses. Below is a breakdown of each of these types of streptococci bacteria.
Also known as streptococcus pyogenes, group A streptococci are most commonly associated with pharyngitis and tonsillitis. Streptococcal pharyngitis is the medical term for strep throat. Although other forms of streptococci can lead to the condition, group A is the most common culprit.
This group can also be responsible for sinusitis, otitis, mastoiditis, pneumonia with empyema, joint or bone infections, necrotizing fasciitis or myositis, meningitis, and endocarditis.
This group of streptococci, otherwise known as streptococcus agalactiae², is most commonly associated with neonatal infections. Its effect on susceptible populations, such as pregnant women, newborns, and the elderly, remains a high source of mortality in those groups.
While group A is commonly associated with pharyngitis, group B more commonly manifests as meningitis, neonatal sepsis, pneumonia in infants and vaginitis, puerperal fever, urinary tract infection, or skin infection in adults.
An example of streptococci that are a normal part of the microbial flora in the human body is enterococcus faecalis³, or group D streptococci. This type of bacteria normally lives in your intestines, where they pose no threat.
However, when the bacteria make their way to other parts of the body, they can cause serious infections. The most common form of infection caused by group D streptococci is urinary tract infection.
As the name implies, streptococcus pneumoniae is most commonly associated with pneumococcal pneumonia. It can also cause meningitis and occult bacteremia. Like group D streptococci, S. pneumoniae is a normal part of the microbial flora in the body.
This type is normally present in the respiratory tract. However, infection from the outside can cause pneumonia and other bacterial infections.
Streptococci groups C and G are rarer than the other types. The most common type is streptococcus anginosus, though one form of them — the streptococcus dysgalactiae subsp. equisimilis (SDSE) — is becoming more common. This strain of bacteria is similar to the group A Streptococcus. pyogenes, commonly associated with throat, skin, and soft tissue infections.
Although the relation of group C and G streptococci to skin and soft tissue infections is clear, there is some doubt about their role in throat infections. While the bacteria have shown up in cultures of people with pharyngitis, they also show up in the throats of healthy people.
Group C streptococci can cause a variety of infections, including the following:
Pharyngitis is a type of sore throat caused by a bacterial infection. Infection from streptococci bacteria is typically referred to as strep throat.
Pharyngitis⁴ is associated with a sudden onset of sore throat, high fever, and pain when swallowing. As a bacterial infection, it's typically spread through direct person-to-person contact.
As mentioned earlier, the exact role of group C streptococci in pharyngitis remains controversial. Although group G has been clearly linked⁵ to outbreaks of pharyngitis, the virulence of group C in human pharyngitis remains unclear.
While studies have shown the bacteria to be present in healthy people and people with pharyngitis, they are found at a higher rate in those with the illness than in the control group. The bacteria's similarity to group A lends further evidence to its role in virulence.
Certain streptococci bacteria in group C are highly associated with bacteremia⁶. This is a dangerous condition that refers to an infection of bacteria in the blood. Bacteremia requires the urgent administration of antibiotics, as a delay in treatment increases the mortality risk of people with it.
People most susceptible to bacteremia infection from group C streptococci are those who already have certain underlying conditions. Depending on the series of bacteria, up to 70% of patients have malignancy, cardiovascular disease, diabetes mellitus, or immunosuppression.
Several types of group C streptococci bacteria can be found as a normal part of a woman's genitourinary flora. Despite this, the bacteria has been attributed to several outbreaks of puerperal fever.
Also known as postpartum infection⁷, puerperal fever caused by group C streptococci is rare. The known incidents were believed to have been caused by environmental factors because the bacteria was traced back to a toilet seat and a bathtub plug.
Infection in infants is also rare. There have been a few cases of meningitis in newborns caused by group C streptococci, but infections of this sort are not common.
Many skin and soft tissue infections can be caused by group C streptococci, including pyoderma, cellulitis, erysipelas, surgical wound infections, abscesses, necrotizing soft tissue infections, and pyomyositis. Among these, cellulitis and erysipelas are particularly common, with group C being responsible in equal or greater frequency than group A.
Group C streptococci can also cause more serious skin infections. These infections include necrotizing fasciitis, Fournier's gangrene, and necrotizing myositis. Here, the dangers of group C clearly outweigh those of group A. Group C is associated with a 33% mortality rate compared to only 11% for group A. These more dangerous infections typically occur in older people with comorbidities.
Bacteria in the streptococci family can also cause an infection in the joints, which results in infectious arthritis. More specifically, streptococcal arthritis. According to the John Hopkins Arthritis Center⁵, streptococcal arthritis goes away when the underlying infection that's causing it clears up. Although this usually happens within 3–12 months, it can last longer for most.
A group of hospitals in France published the occurrence of various streptococci strains in infectious arthritis patients. SDSE was found in 12% of patients and S. anginosus in 11%. These incident rates were second only to the group B type S. agalactiae.
As we've seen, several members of group C streptococci are normal parts of the human microbial flora. So their presence does not mean a course of treatment must be pursued. However, treatment is recommended if the bacteria has caused an infectious illness.
The typical treatment for group C streptococci is the antibiotic penicillin. The need for treatment grows more urgent when the bacteria is causing life-threatening conditions, such as bacteremia or one of the deadly skin infections.
Although less common as a cause of illness than some other groups, infection with strep group C can cause various adverse medical conditions. Some of these conditions can be life-threatening, particularly in older or immunocompromised patients. Group C infections can be treated with prescription antibiotics, most commonly penicillin.
If you believe you may have one of the conditions described above, make an appointment with your doctor. They'll be able to help determine the cause of your illness and which, if any, strep groups are playing a role in it.
Strep group C can cause a range of different illnesses. Some of the infections that the group can cause are quite serious. These include infection of the blood, known as bacteremia, and several skin infections that can be deadly. If you aren't feeling well, it's always best to see a doctor to rule out serious illness.
Yes. Strep group C can spread from person to person as a bacterial infection. Although most forms of group C are spread this way, it's also possible for the bacteria to spread to humans through animal contact, such as contaminated meat products.
Streptococci bacteria can be split into several groupings. The groupings are differentiated by letter. If you see the letter C on a strep test, the bacteria causing your infection comes from streptococci in group C.
Chapter 13: Streptococcus (1996)
Pharyngitis (strep throat) | Centers for Disease Control and Prevention
Postpartum infection (2022)