Necrotising fasciitis and Group C & G streptococci

Group C and G streptococci

What are Group C & 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.

Where does Group C & G Strep normally live?

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.

Group C & G streptococci infections

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.

Surface infections that are not serious in themselves include sore throat (pharyngitis) and impetigo.

Unlike group A strep infections, Group C and G strep surface infections do not commonly lead to immune complications such as rheumatic fever. Rarely, post-strep glomerulonephritis (kidney inflammation) can occur after group C infection.

Deeper infections caused by Group C & G Strep

• Skin and soft tissue infection (Cellulitis; rarely necrotising fasciitis)
• Arthritis (joint infection)
• Pneumonia
• Rarer infections e.g. endocarditis (heart valve infection), neonatal infection, puerperal infection (childbirth-related)
• Bacteremia (bacteria in the blood/blood poisoning)

Complications of deeper infections can include septic shock and toxic shock, though this is rarely reported and is more common with group A strep disease.

Find out more about each infection below:

Group C and G related necrotising fasciitis

Necrotising fasciitis can be caused by a number of bacteria, though the group A strep is a leading cause in about half of all cases that occur in the community setting. Group C and G can also cause this condition, though rarely.

If streptococci spread below the thick layers under the outer skin surface, they will reach the connective tissue or “fascia” These are the fibrous bands of tissue which separate muscle bundles. Arranged in layers, with blood vessels and fats within them, these fascia provide a “freeway’ for streptococci to spread. Again, the immune response will attempt to contain the infection but, in some cases, the bacteria will succeed in establishing an infection. As the infection is deep and well below the outer skin, redness and swelling of the skin may not occur (unless there is cellulitis as well). The classical symptom is severe pain, in association with a fever or other ‘flu-like symptoms.

Skin changes may begin to occur in the later stages of illness and include blistering and colour change. This is usually a clear sign that tissue in the fascia has died as a result of infection. Antibiotics will normally be administered quickly to assist in killing bacteria, but the main aim of treatment will be to remove as much dead or dying tissue as possible. This will involve surgery, which may be carried out repeatedly, as surgeons attempt to identify dead areas of tissue and preserve parts that are not dead. Sometimes surgery is quite disfiguring, due to the part of the body involved, or the extent of disease. There is a difficult balance between preserving normal body shape and performing surgery, which may be life-saving. Plastic surgery may be required in the convalescent period. Some cases of necrotising fasciitis due to strep are complicated by bacteremia (bacteria spreading into the bloodstream) and septic or toxic shock. Patients who are particularly ill may be nursed in the intensive care unit. Sometimes, patients are given intravenous immunoglobulin (“IVIG”) which is an infusion of antibodies purified from large numbers of blood donations. Antibodies are proteins made by the immune system to fight infection; IVIG might help the body’s immune response to the streptococcal toxins and bacteria causing disease, although there have been no clinical trials that show this yet (and it has not particularly been used for group C or G strep infection).

Streptococci tend to affect the arms, legs, or less commonly, the trunk of the body. It is important to recognise that other bacteria can also cause necrotising fasciitis. Roughly half of all cases of NF are due to other bacteria which act as a ‘team’ to cause a similar aggressive infection which results in the death of tissues in the fascia. These cases often follow surgery or injury to the abdominal wall. Diabetics are more prone to the condition. Bacteria from the bowel or groin area team up with other common skin bugs to invade the tissues of the abdominal wall (sometimes known as “Meleney’s synergistic gangrene”) or in the groin (sometimes known as “Fournier’s Gangrene”). In these cases, the layers of tissue immediately under the skin are often involved as well, and the infection is often more obvious. Distinguishing a simple post-surgical wound infection from necrotising fasciitis can sometimes be difficult but worsening of symptoms, blood tests, and skin changes provide good evidence. As with strep necrotising fasciitis, surgery to remove all dead tissue is essential, along with antibiotics that kill all the likely bacteria.