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S. pyogenes infections are worldwide in distribution.
· Prevalence of streptococcal pyoderma is higher in tropics with no seasonal variation, whereas it is more common in winter months in temperate countries.
· Rheumatic fever is most frequently observed in children aged5–15 years, the age group most susceptible to S. pyogenesinfections. The attack rate of rheumatic fever following upper respiratory tract infection is approximately 3% for persons with untreated or inadequately treated infections.
Streptococci are normal flora of the oral cavity, nasopharynx, skin, fingernails, perianal region, intestine, and upper respira-tory tract of humans.
Infected human cases are the reservoirs of infection. Respiratory and salivary secretions in the form of droplets and contami-nated fomites are the sources of S. pyogenes infection.
Streptococcal carrier rate as high as 20–40% has been reported. However, these carriers with chronic asymptomatic pharyngeal and nasopharyngeal colonization are not usually at risk of spreading disease, as they mostly inhabit avirulent organisms.
· Person-to-person transmission is the main route of trans-mission. The infection is transmitted from person to person through respiratory droplets. The infection is also trans-mitted through breaks in the skin by direct contact with infected patient, fomites, or arthropod vectors. Children with untreated acute infections spread organisms by their salivary droplet and nasal discharge.
· Occasional food-borne and waterborne outbreaks have also been documented.
Overcrowding (crowded homes and class rooms) is an impor-tant factor in transmission of S. pyogenes infection. Both impe-tigo and pharyngitis are more likely to occur in children living in crowded homes and under poor hygienic conditions.
Bacteriocin and phage typing of streptococci are employed in research and epidemiologic studies.
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