Is ASO titre alone an indicator of rheumatic fever?

Q: Recently, my eight-year-old son was down with fever (100-103 deg F) for two days. He had cough, intermittent headache and vomiting. He occassionally used to complain of pain in muscles of thigh or arm / forearm, but not essentially joint pains. There was never any swelling or redness over joints. He has enlarged tonsils and gets throat infection 2-3 times in a year. His routine blood investigations were normal. ESR was 7 mm fall in the first hour, CRP was 0.23 mg and ASO titre was 246 todds. His throat infection was treated with Cefadroxil. Presently, his fever has subsided, but he is still on medication. Is ASO titre alone an indicator of rheumatic fever to start the treatment with penicillin in the absence of any other major or minor criteria? What all tests should be done to arrive at a final diagnosis, and after how many days of stopping the treatment for recent infection? Is there any need of repeating ASO titre now? What are the other conditions where ASO titre is raised? Though the upper limit of ASO titre is 200 todds, is 246 todds clinically significant to consider a diagnosis of rheumatic fever? Is there any need to go for tonsillectomy as he gets throat infection 2-3 times in a year?

A:I will answer your questions pointwise.

1. No, the ASOT elevation alone is not an indicator to start treatment for acute rheumatic fever. This is as the attack rate of Streptococcus to cause rheumatic fever is 5 per cent, but the ASOT rises in 85 per cent of children who have a strep sore throat.
2. It is good to have a throat swab as well, prior to starting treatment. An elevated ASOT takes a few weeks to develop, and this is likely to be a dated infection. There is no role of repeating ASOT.
3. There are other streptococcal infections / immune reactions to strep where the ASOT is elevated.
4. Elevated ASOT is one of the mandatory criteria, but on its own without major and minor manifestations does not suggest acute rheumatic fever.
5. Currently there is no role for a tonsillectomy.