Group C and G streptococci

Group C and group G streptococci are bacteria closely related to the group A streptococcus (sore throat or flesh-eating bug) which look like small round beads under the microscope and which produce a range of toxins and surface proteins which combat the human immune system and also cause disease. Unlike the group A streptococcus, the group C and group G streps have not been studied extensively. This is mainly because the diseases due to group C and G are much less common, but also because the diseases caused are less well-recognised. Latin names used to describe some of the members of these two groups include Streptococcus equi, Streptococcus equi subspecies zooepidemicus, Streptococcus equisimilis, and Streptococcus dysgalactiae.

Although Group A strep normally live in people’s throats and can spread in the community from person to person, we know that group C and G streptococci most commonly live on animals such as horses and cattle and can spread to humans through raw milk or contact with animals. However, both types can live in people’s throats and probably spread like the group A strep. Food and milk-borne epidemics of group C or G sore throat used to be commoner, but with pasteurisation, this is rare nowadays. In fact, most people with group C or G strep disease have no history of contact with animals or raw dairy products.

Group C and G streps also can live on the skin, particularly where the skin is damaged by conditions such as eczema, as well as on any other mucous surface of the body, such as the vagina and bowel. They cannot survive for very long away from these types of environment.

Recognition of invasive group C and G streptococcal disease is rising. Unlike group A streptococcal disease, patients with serious group C or G strep disease usually suffer from other medical conditions. Indeed, cases are commonest in people over 75 years of age. For reasons not completely understood, men seem to be at greater risk of group G streptococcal disease.

Despite the link to animals, few people with invasive group C or G streptococcal illness have any history of contact with farm animals or horses. The vast majority of group C and G disease is picked up in the community - they are not normally considered to be ‘hospital infections’, even in patients following surgery.

Although deep infections can easily be treated with antibiotics, we know that some people can die from this type of infection, especially when the bacteria have spread into the bloodstream (bacteremia). Sometimes the blood pressure may fall suddenly and cause other parts of the body to fail (septic shock). The risks are somewhat less than for group A strep disease, but often the patients with group C and G disease may be more frail to start with. There have been a few reports of ‘toxic shock’ with group C and G infections.

Depending on the position in the body where the infection is based, it may be necessary for surgery to be performed to, for example, drain pus from a joint, or replace a heart valve.

By Shiranee Sriskandan FRCP. PhD. Imperial College London