The most common cause of bacterial pharyngitis is the Lancefield group A, Streptococcus pyogenes.
Healthy carriers of group A streptococci are usually children in whom rates of up to 20% - 30% have been reported, but rates are much lower in adults (5% - 15%).
In these individuals isolation of Lancefield group A streptococci does not necessarily imply a role in infection.
Extrapharyngeal manifestations of Lancefield group A streptococcus infection can be divided into those associated with acute infection and the nonsuppurative post streptococcal sequelae such as acute rheumatic fever and glomerulonephritis, which occur 2-3 weeks after pharyngeal infection.
In acute infection, bacteraemia and streptococcal toxic shock may occur. Post streptococcal sequelae appear to be limited to a circumscribed set of serotypes.
Lancefield group C streptococci have been reported as a cause of pharyngitis - Streptococcus dysgalactiae subspecies dysgalactiae.
The Lancefield group G streptococci are known to cause pharyngitis.
Most of the evidence for Lancefield groups C and G streptococci causing pharyngitis
comes from reports of outbreaks.
Source - standards for microbiology investigations.
So it could be a group C or G strep?