Enhanced recovery of Haemophilus ducreyi from clinical specimens by incubation at 33 versus 35 degrees C

Isolation rates of Haemophilus ducreyi from cases of chancroid are low. Experts recommend that isolation media be incubated at 33 to 35 degrees C, but the possible effect of this temperature range on the recovery of H. ducreyi has not been evaluated. We inoculated two sets of agar plates with material from genital ulcers and incubated one set at 33 degrees C and one at 35 degrees C; incubation at 33 degrees C identified 21% more cases than did incubation at 35 degrees C (109 versus 85 cases, respectively, of the 116 cases from which an isolation was made; P < 0.01).