Group A Beta Haemolytic Streptococcus (GABHS)

Group A β haemolytic streptococcus (streptococcus pyogenes) is the infective agent responsible for the most serious complications of tonsillopharyngitis (image, above, reproduced with permissions from CDC).

The M protein GABHS is associated with diseases outside the pharynx, and it is the similarity of some of the serotypes to myocardial sarcolemma antigens that is responsible for the development of rheumatic fever in some patients.

A different process of antigen/antibody complex deposition in glomeruli is responsible for the development of post-streptococcal glomerulonephritis.

Exotoxins

GABHS may also release a variety of exotoxins which are responsible for illnesses such as toxic shock syndrome and necrotising fasciitis. One of these exotoxins, streptolysin O, provokes a reliable immune response which can be measured via the antistreptolysin O titre (ASOT), a standard marker of GABHS infection.

Carriage rates

GABHS may be carried asymptomatically, maximally between the ages of 3 and 15, where carriage rates have been found between 5% and 21%. In adults, the rates are far lower, lying between 2.4% and 3.7% [5].

Complications

Untreated GABHS infection normally lasts between 8-10 days with patients remaining infectious during, and one week after, the illness. Complications of GABHS infection are categorised into suppurative and non-suppurative.

Suppurative complications

Suppurative complications such as otitis media, sinusitis and peritonsillar abscess arise from direct spread of infection into adjacent structures.

Non-suppurative complications

Non-suppurative complications are far rarer with the most common, rheumatic fever, having an annual incidence of less than 10 cases per 100,000 in western Europe and the USA [6].

However, 95% of new cases worldwide occur in the developing world (6) where rheumatic fever remains a significant problem and is responsible for approximately 500,000 deaths annually [7].

Learning bite

Although rheumatic fever is a rare complication of GABHS infection in the western world, it remains a significant problem in the developing world.