G6PD and infection: Class A, with median G6PD activity <20%, is associated with chronic non-spherocytic hemolytic anemia; variants having <20% activity and only acute hemolytic anemia triggered by oxidant drugs, fava beans, or infections are grouped into Class B. Class B (median G6PD activity <45%) encompasses most common polymorphic variants and entails risks of severe neonatal jaundice and acute hemolytic anemia from such stimuli, incorporating former Class II and III.