What is the likely cause of the symptoms described in a child recovering from a severe sore throat, including chest pain and swollen joints?

The symptoms described in the child, particularly chest pain and swollen joints following a severe sore throat, strongly suggest rheumatic fever. This condition is a known complication of untreated or inadequately treated streptococcal throat infections, commonly caused by Group A Streptococcus.

Rheumatic fever typically manifests several weeks after the initial sore throat infection and can result in a constellation of symptoms, including fever, joint inflammation (arthritis), heart involvement (which may explain chest pain), and other systemic effects. The pathophysiology involves an autoimmune response where antibodies produced against the streptococcus bacteria mistakenly attack the body's own tissues, particularly in the heart, joints, skin, and nervous system.

In contrast, pneumonia often presents with respiratory symptoms, such as cough and difficulty breathing, rather than joint pain or chest pain that follows a sore throat. A viral infection may lead to similar symptoms but usually would not cause significant joint pain or link directly with the previous symptoms of a sore throat in this context. Asthma exacerbations primarily involve airway obstruction and respiratory symptoms rather than joint swelling and chest pain. Therefore, the combination of a recent severe sore throat followed by the indicated symptoms makes rheumatic fever the most plausible diagnosis in this scenario.