Strep C (Group C Streptococcus) is a collection of bacteria within the Streptococcus genus that can cause illness in humans. While less common than Strep A or Strep B, Strep C can lead to a range of diseases, from mild infections like a sore throat to potentially severe conditions. Like its relatives, Strep C infections are generally treated effectively with antibiotics.
Classification and Defining Features
Strep C is classified using the Lancefield grouping system, which categorizes Streptococcus species based on carbohydrate antigens on their cell walls. The “C” refers to the unique C antigen structure expressed by these bacteria. This system aids in the clinical identification of different streptococcal types.
These bacteria are characterized as Gram-positive cocci, appearing purple and spherical under a microscope. They typically grow in chains, a characteristic shared by all Streptococcus species. Most Strep C strains exhibit beta-hemolytic activity, meaning they produce toxins that completely destroy red blood cells when grown on a blood agar plate.
The group C designation includes several species, with Streptococcus dysgalactiae subspecies equisimilis being the most common cause of human infection. This species is closely related to Group A Streptococcus (S. pyogenes) and shares similar virulence factors. While the Lancefield grouping provides quick identification, modern techniques offer more detailed species-level identification.
Sources and Transmission Pathways
Strep C is often considered a zoonotic pathogen, meaning it can be transmitted from animals to humans, though person-to-person spread is also common for certain strains. Primary reservoirs for some species, such as Streptococcus equi subspecies zooepidemicus, are livestock like horses and cattle. These animal-associated strains can cause significant disease in their host animals.
Transmission to humans occurs through direct contact with infected animals or consumption of contaminated food products. Outbreaks have been linked to ingesting unpasteurized milk or dairy products containing the bacteria. Individuals with occupational exposure, such as farmworkers or veterinarians, face a higher risk of direct animal-to-human transmission.
The species most frequently isolated from human infections, Streptococcus dysgalactiae subspecies equisimilis, is adapted to humans. It often resides harmlessly in the human upper airway, skin, and gastrointestinal tract. Transmission of this strain typically occurs through person-to-person contact via respiratory droplets or contaminated surfaces, similar to Strep A.
Range of Human Infections
Strep C infections range from localized, mild illness to severe, invasive disease. The most common presentation is pharyngitis (strep throat), often occurring in outbreak settings. Symptoms are similar to Strep A, including a sore throat, fever, and sometimes white patches or pus on the tonsils.
The bacteria can also cause skin and soft tissue infections, such as cellulitis, characterized by painful, swollen, and warm areas of skin. Less frequent manifestations include deep-seated infections like septic arthritis or osteomyelitis, affecting the joints and bones. These infections develop when the bacteria enter the body through a break in the skin or spread from a colonization site.
Invasive disease occurs when the bacteria enter the bloodstream, known as bacteremia. From the bloodstream, Strep C can travel to various organs, potentially causing endocarditis (inflammation of the heart lining or valves). Invasive infections are rare but are more likely in individuals with underlying medical conditions, such as those who are immunocompromised or have chronic illnesses.
Detection and Treatment Strategies
Diagnosis begins with a physical examination and assessment of symptoms. For suspected strep throat, a throat swab is taken to test for the bacteria. The sample can be analyzed using a rapid antigen detection test or a throat culture, which is the diagnostic standard.
If a widespread or invasive infection is suspected, blood cultures confirm the bacteria’s presence in the bloodstream. Once isolated, the bacteria are identified as Group C Streptococcus using the Lancefield grouping test. Accurate identification helps healthcare providers choose the most effective course of treatment.
The standard treatment involves antibiotics, with penicillin being the drug of choice due to the bacteria’s sensitivity. Amoxicillin is a highly effective alternative, often preferred for ease of administration. For patients with a penicillin allergy, options include cephalosporins or macrolides.
Patients must complete the entire prescribed course of antibiotics, even if symptoms improve quickly. This ensures all bacteria are eliminated and prevents potential complications or antibiotic resistance. Treatment of invasive infections often requires prolonged intravenous antibiotics to fully eradicate the bacteria.