Further investigation of acute Q fever patients with M. pneumoniae IgM revealed that few had 4-fold increases (3.6% and 11.1%) and IgG seroconversion (28.6% and 11.1%) as measured by the two ELISA kits (Table 3), indicating that the presence of IgM did not result from true infection. The gene discussed is CD40LG; the disease is Q fever.