CD40LG and leptospirosis: Therefore, if acute-phase IgM had been used to diagnose acute leptospirosis instead of paired serum specimens, only 21 of 120 acute infections would have been identified (sensitivity 17.5%, 95% CI 11.2%–25.5%), and 201 of 653 patients without acute leptospirosis would have been given an erroneous diagnosis (specificity 69.2%, 95% CI 65.5%–72.7%).