Of 30 case patients, six (20%) case patients had evidence of another acute arboviral infection (four had evidence of confirmed or probable WNV and two with POWV) and 20 (67%) had test results that showed cross-reactivity, false-positive IgM results that did not confirm with PRNT, or a previous infection (i.e., IgG antibodies) with another arbovirus (LACV or WNV). The gene discussed is CD40LG; the disease is infection.