Amongst the bacteria pathogenic for man, few show such variety in clinical manifestations and epidemiology as the streptococci. Streptococcus pyogenes (Lancefield group A) in particular has attracted much attention over the years as one of the major human pathogens and it remains very common as a cause of skin infection throughout the world, despite the availability of antibiotics. There is an increasing appreciation of other haemolytic and non-haemolytic streptococci in clinical specimens and in disease as a result of the growing use of streptococcal identification and Lancefield grouping kits in laboratories.

Skin infection with streptococci covers a range from simple colonization to primary and secondary infections; the skin provides an important portal of entry for systemic infection by these organisms. Skin infection may be complicated by non-suppurative sequelae such as nephritis and scarlet fever; conversely, streptococcal infection at other sites in the body may lead to skin manifestations, as in rheumatic fever and acute guttate psoriasis. The following account will consider these conditions, excluding streptococcal infections of the mouth, alimentary, respiratory and genitourinary tracts or deeper structures except insofar as they are relevant to the skin.

Biology and classification of streptococci

As a group the streptococci are Gram-positive, spherical, aerobic and facultatively anaerobic bacteria arranged in chains or pairs, non-sporing, catalase negative, oxidase negative and mainly non-motile. They ferment carbohydrates with the production of lactic acid but no gas, and they fail to reduce nitrate.