What are the triggers for Henoch-Schönlein Purpura (HSP)?

Triggers for Henoch-Schönlein Purpura (HSP)

Infections are the most frequent triggers of HSP, particularly upper respiratory tract infections caused by group A streptococcus, which accounts for approximately 17% of cases. 1, 2

Primary Infectious Triggers

Bacterial Infections

• Streptococcal infections are the most common bacterial trigger, identified in 17.08% of HSP cases, particularly group A streptococcus causing pharyngitis or tonsillitis 1, 3, 2
• Helicobacter pylori infection accounts for 5.92% of cases 1
• Mycoplasma pneumoniae is identified in 4.83% of cases 1, 2
• Subacute bacterial endocarditis has been documented as a rare but important trigger, with HSP resolving after treatment of the underlying endocarditis 3

Viral Infections

• Parainfluenza virus is identified in 0.5% of cases 1
• Respiratory syncytial virus accounts for 0.08% of cases 1
• Epstein-Barr virus has been implicated as a trigger 1
• Influenza A (H1N1) infection has been associated with HSP 4

Parasitic Infections

• Toxoplasma gondii has been identified in rare cases (0.08%) 1

Vaccination-Related Triggers

• Influenza vaccination has been documented as a trigger, particularly during the 2009 H1N1 pandemic, though the absolute incidence remains very low 4
• Cases typically develop within weeks of vaccination, with clustering observed in October-November 2009 4
• Caution is warranted in children with prior immunologically-mediated diseases (previous HSP, drug eruptions, food allergies), though vaccination should not be routinely withheld 4

Non-Infectious Environmental Triggers

• Cold exposure has been associated with HSP onset 2
• Insect bites can trigger the condition 2
• Drug allergies are recognized triggers 5, 2
• Food reactions have been implicated 2
• Toxin exposure may precipitate HSP 5

Underlying Systemic Conditions

• Malignancy can serve as a triggering factor 5
• Systemic diseases may precipitate HSP 5

Epidemiological Patterns Suggesting Trigger Influence

• Seasonal variation is evident, with HSP occurring more commonly in spring and winter than summer, consistent with respiratory infection patterns 1
• Geographic gradient exists (west-to-east in Anhui province, China), suggesting regional variation in infectious agent exposure 1
• Approximately 50% of cases have identifiable infectious triggers on admission 1

Clinical Implications for Management

• Complete elimination of infectious triggers significantly improves remission rates of purpura (p<0.01), supporting the use of adjunctive anti-infectious agents when infection is identified 1
• Etiological investigations are required as a triggering factor is found in approximately half of patients 5
• Infection remains the most frequent trigger regardless of clinical phenotype (renal, gastrointestinal, or isolated cutaneous) or whether the case represents initial presentation or relapse/recurrence 1

Important Caveats

• Not all HSP cases have identifiable triggers; more than 40-50% of cases lack a clear precipitating factor 1, 5
• The temporal relationship between trigger exposure and HSP onset varies, typically occurring days to weeks after the inciting event 3, 4
• While vaccination-associated HSP has been documented, the extremely low incidence does not justify withholding recommended vaccinations in the general population 4