Haemophilus

The genus Haemophilus in the family Pasteurellaceae are worldwide occurring, immobile, mostly aerobic, rarely anaerobic (facultative anaerobic), gram-negative, coccoid, sporeless rod bacteria found in humans and animals. In humans, a small percentage colonize the nasopharynx without causing symptoms. Vaginal colonization is also possible. So far, 16 species are known. Haemophilus bacteria can occur as encapsulated ("typable") or unencapsulated strains ("non-typeable" or NTHi). Some Haemophilus species cause relevant diseases in animals (Haemophilus parasuis is the causative agent of febrile polyserositis and polyarthritis; Haemophilus paragallinarum is the causative agent of contagious chicken rhinitis).

Species relevant to human medicine are:

• Haemophilus aegypticus (causative agent of contagious infectious conjunctivitis and Brazilian purple fever = haemolytic prupura)
• Haemophilus ducreyi (causative agent of ulcus molle; causative agent of non-venereal chronic ulcers in the tropics)
• Haemophilus haemolyticus (apathogenic colonizer of the nasopharynx)
• Haemophilus influenza (causative agent of meningitis in children, chronic bronchitis, otitis media, osteomyelitis, pericarditis, OPSI in splenectomized patients). Note: H. influenzae was the first organism to be completely sequenced in 1995).
• Haemophilus parahaemolyticus (causative agent of oral cavity infections, endocarditis)
• Haemophilus parinfluenzae (causative agent of endocarditis)

The examination for Haemophilus species is based on the cultivation, identification and typing of the pathogen from patient samples. Culture-independent methods include direct microscopy of body secretions and detection via polymerase chain reaction (PCR). In addition, antigen detections for CSF diagnostics are commercially available.

Note: Diagnostic specimens should always be collected before starting antibiotic therapy. In case of doubtful isolates, PCR detection of specific hi-genes can confirm the diagnosis. Mass spectrometric identification(MALDI-TOF) is also a well-established method and can provide clarity in this regard.

Bacteria of the genus Haemophilus require certain growth factors from the blood. H. influenzae requires both factor X and factor V. Other species require only one or the other factor. Important classification criteria for individual Haemophilis species are the biochemical structure of the capsular polysaccharides.

1. Hof H et al (2019) Haemophilus. In: Hof H, Schlüter D, Dörries R, eds Duale Reihe Medizinische Mikrobiologie. 7th, completely revised and expanded edition. Stuttgart: Thieme p 436-439

2. van Hattem JM et al. (2018) Haemophilus ducreyi cutaneous ulcer contracted at Seram Island, Indonesia, presented in the Netherlands. PLoS Negl Trop Dis 12:e0006273.