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ANSWER:It is important to remember the following facts about Group A beta-haemolytic Streptococcal (GABHS) upper respiratory tract infection (such as sore throat) and rheumatic fever:

1. Group A Streptococci produce beta-haemolysis (i.e. complete haemolysis) on sheep blood agar (a bacteriological culture media) hence they are known as GABHS.
   
2. Not all patients with GABHS infection will get rheumatic fever. Only a minority of patients (according to some reports around 3%) get this non-pyogenic or non-pus forming complication of GABHS infection.
   
3. Localised clinical presentation of the throat such as pharyngitis or tonsillitis and pyogenic complications such as peri-tonsillar abscess, retro-pharyngeal abscess, otitis media are much more common with GABHS than the distant complications.
   
4. GABHS can colonise the throat without causing infection. Therefore other potential causes of throat infection or inflammation should be excluded even when the culture or antigen detection test results demonstrate the presence of GABHS.
   
5. The presence of significantly raised antibodies against Streptolysin O (or raised ASO titre as in this case) would be consistent with infection rather than colonisation. However, in individuals with recurrent infection with GABHS the ASO titre might be raised from an earlier infection. Hence demonstration of a significant change in ASO titre is more important than a single “positive” or high titre in an age group where such infections are common. In children ASO titres in excess of 320 Todd units/ml is considered to be clinically significant.
   
6. The occurrence of rheumatic fever and its manifestations after GABHS infection of the throat is dependent on several factors which may include socio-economic (more common in developing countries), serotype of GABHS (M-protein serotypes (for example, 1, 3, 5, 6, 18, 24), virulence of the strain, recurrence of infection, age of onset of illness, administration of antibiotics and possible genetic predisposition to the development of rheumatic fever.
   
7. Early administration of appropriate antibiotics (usually within 9 days of onset of the GABHS associated throat infection) seems to diminish the chance of occurrence of rheumatic fever.
   
8. The treatment of GABHS infection of throat usually involves a 10-day course of an appropriate antibiotic (usually of the penicllin, macrolide group). The selection of the appropriate antibiotic depends on clinical judgement and discretion.
   
9. One should consult a paeditrician to rule out the presence of complication and direct appropriate management.

Answered by:  Dr Sanjay Bhattacharya    |  Associate Consultant, 
Department of Microbiology, 
Tata Medical Center, Kolkata