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The role of normal skin in the spread of streptococcal pyoderma
Abstract:
The primary body site of acquisition of group A streptococci was examined prospectively in a population with endemic streptococcal pyoderma. Weekly cultures were obtained during the skin infection season from apparently normal upper respiratory and cutaneous sites (and from skin lesions when present) in 44 children and adults living on the Red Lake Indian Reservation.During the 9-week period of the study 705 of a total of 2305 cultures were positive for group A streptococci. The percentage of positive cultures from the various sites were: throat (20%); nose (24%); wrist (32%); ankle (35%); back (22%); and skin lesions (81%). Group A streptococci were also isolated from fingernail dirt, clothing and bedding as well as from a few household pets and insects.Analysis of serial cultures obtained from the same individuals at weekly intervals suggested that the strains isolated from skin lesions first appeared on normal skin in the 2 weeks preceding the lesion. Spread to the nose and throat followed skin acquisition and/or skin lesions.The high prevalence of group A streptococci on normal skin in the absence as well as the presence of pyoderma, and their appearance on normal skin before recovery from either skin lesions or the upper respiratory tract are consistent with the view that skin acquisition was a primary predisposing factor to pyoderma. Since the literature indicates that group A streptococci are rarely part of the normal skin flora, these findings raise the possibility of unique biological properties of these and perhaps other pyoderma strains, as distinct from other group A streptococci.
Insights
Group A Streptococcus acquisition primarily occurs on the skin, preceding pyoderma development. This suggests skin colonization is a key factor in streptococcal skin infection, differing from typical skin flora patterns.
Area of Science:
- Microbiology
- Dermatology
- Epidemiology
Background:
- Group A Streptococcus (GAS) is a significant pathogen causing various infections.
- Streptococcal pyoderma is endemic in certain populations.
- The primary site of GAS acquisition is not fully understood.
Purpose of the Study:
- To prospectively identify the primary body site of Group A Streptococcus acquisition.
- To investigate the relationship between skin colonization and pyoderma development.
- To explore potential unique properties of pyoderma-associated GAS strains.
Main Methods:
- Prospective weekly culturing of respiratory and cutaneous sites in 44 individuals.
- Inclusion of normal skin and active skin lesions.
- Serial culture analysis to determine acquisition sequence.
Main Results:
- GAS was frequently isolated from normal skin (wrist, ankle, back) and skin lesions.
- Skin colonization preceded the development of skin lesions and upper respiratory tract infections.
- GAS was also found on indirect fomites and household contacts.
Conclusions:
- Skin acquisition appears to be a primary predisposing factor for streptococcal pyoderma.
- The high prevalence on normal skin suggests unique adaptations of pyoderma-associated GAS strains.
- Findings challenge the notion that GAS is rarely part of normal skin flora.