Q: Treatment of which infection found to show improvement in Idiopathic thrombocytopenic purpura (ITP)?

Answer: Helicobacter pylori

Interestingly, for mechanism not fully understood, particularly in adults who lives in areas with a high prevalence of Helicobacter pylori, diagnosis and treatment of Helicobacter pylori infection has shown to improve platelet counts in many patients.

Reference:

Stasi R, Sarpatwari A, Segal JB, Osborn J, Evangelista ML, Cooper N, Provan D, Newland A, Amadori S, Bussel JB (2009). "Effects of eradication of Helicobacter pylori infection in patients with immune thrombocytopenic purpura: a systematic review". Blood 113 (6): 1231–40.