Childhood Langerhans cell histiocytosis increased during El Niño 1997-98: a report from the Taiwan Pediatric Oncology Group.

From 1995-1999, a nation-wide study of Langerhans cell histiocytosis (LCH) in children less than 15 years old was conducted by the Taiwan Pediatric Oncology Group. The demographic and clinical data of 55 cases were analyzed. Thirty-two cases presented from the beginning of 1997 to the end of 1998, when the most severe El Niño in the century occurred. The incidence was higher than expected during this El Niño period (32 cases versus 22 cases, p = 0.003). During 1997-98, most LCH was diagnosed in summer (n = 15), autumn (n = 8), and winter (n = 8) but rarely in spring (n = 1); coincidentally, rainfall was least in winter but peaked in summer. During 1997-98, the most significant increase occurred in the polyostotic LCH subcategory (p = 0.017), with younger ages at diagnosis (p = 0.039). The incidence of LCH cytopenia, fever, and diseases of the skin, liver, spleen or other organs did not differ significantly. Local treatment modality, disseminated diseases and diagnosis during the El Niño of 1997-98 were independent risk factors predicting the recurrence or progression of LCH. Our findings suggest that particular infections or other environmental factors associated with El Niño might be related to the etiology of childhood LCH.