Seroconversion of a negative first sample to a positive second sample or a fourfold or higher rise in titer can be considered diagnostic of a recent or current infection.[1] A high IgM titer with ELISA can be indicative of a current or recent infection; however, IgM levels can remain detectable for several months to years so elevated IgM levels cannot positively confirm a diagnosis of leptospirosis.[1]. This evidence concerns the gene CD40LG and infection.