Final answer:
Sydenham's chorea, characterized by involuntary movements, is a criterion for diagnosing rheumatic fever following a group A strep infection, which can lead to comorbidities like arthritis and carditis. It requires treatment with antimicrobial therapy to address the underlying infection and prevent heart valve damage.
Step-by-step explanation:
The child with group A strep suspected of having rheumatic fever, and now displaying involuntary irregular movements of limbs and face, is exhibiting signs consistent with Sydenham's chorea, also known as rheumatic chorea. This is one of the major criterias for the diagnosis of rheumatic fever, a serious sequela of streptococcal pharyngitis. The diagnosis is based on a combination of clinical findings and history of recent strep infection. Rheumatic fever can also have other comorbidities such as arthritis and carditis, which can lead to heart murmur due to valve damage.
Antimicrobial therapy is important in treating the underlying streptococcal infection to prevent further acute-phase proteins reaction and to diminish the severity of acute rheumatic fever's symptoms. The disease requires careful management because of the risk of recurrences and long-term complications, such as rheumatic heart disease. Therefore, early detection and treatment is crucial for better outcomes.