Haemophilus paraphrophilus infection: a pitfall in laboratory diagnosis

Many clinical laboratories have difficulty in identifying a group of organisms which are catalase negative, oxidase positive, Gram negative rods. We describe a case of purulent sacroiliitis due to Haemophilus paraphrophilus where the organism was initially misidentified as Eikenella corrodens leading to inappropriate antimicrobial chemotherapy. We review the strains of H. paraphrophilus and E. corrodens that were identified by the National Collection of Type Cultures over the last ten years. Only 21 of 100 strains identified as E. corrodens were submitted as E. corrodens. Seven strains submitted as possible E. corrodens were identified as H. paraphrophilus. Several different species of Gram negative rods may produce pitting on agar and this seems to be poorly recognised. However, further tests are available to facilitate correct identification of these strains.