Microbiology
Gram-negative coccobacillus. H. aprophilus (now Aggregatibacter aphrophilus), H. ducreyi, H. haemolyticus (Can be confused with H. influenza in the COPD patient but is not a pathogen (PubMed), H. influenzae, H. parahaemolyticus, H. parainfluenzae, H. paraaprophilus, Haemophilus segnis (now Aggregatibacter segnis).
Epidemiologic Risks
Being human, and, for Type b H. influenza, being an unvaccinated human.
H. influenza can be type b, other types (a,c,d,e, f as examples) and untypable.
Kids used to get type b, adults usually get other types or untypable. The vaccine has pretty much eradicated b disease.
H. influenza type a can also cause invasive disease (PubMed), and along with untypeable strains, is increasing (PubMed).
Syndromes
H. influenzae: otitis media, sinusitis, epiglottitis, pneumonia, meningitis (especially children who are not vaccinated). And urethritis (PubMed).
Invasive disease should result in a workup for antibody deficiencies and other immunodeficiencies (PubMed).
7% of patients under age 40 with bacteremia from Streptococcus pneumoniae, Streptococcus pyogenes group A, Neisseria meningitidis, Neisseria gonorrhoeae, or Haemophilus influenzae will die and 25% will be readmitted in the subsequent two years. They have immunologic issues: low immunoglobulins or a complement deficiency (Pubmed).
H. ducreyi: chancroid, painful, ulcerated, genital ulcers with inguinal adenopathy. In the developing world, it causes chronic skin ulcers in children (PubMed).
H. aprophilus (now Aggregatibacter aphrophilus), parainfluenza and paraaprophilus: endocarditis. Part of any disease where spit is an issue.
Treatment
H. influenzae: any and all beta-lactams (except ampicillin) and quinolones. See specific diseases. Type b with increasing resistance to ampicillin.
H. ducreyi: azithromycin 1 g orally in a single dose OR ceftriaxone 250 mg (IM) in a single dose OR ciprofloxacin 500 mg orally twice a day for 3 days OR erythromycin base 500 mg orally three times a day for 7 days (CDC).
H. aprophilus, parainfluenza and paraaprophilus endocarditis: ampicillin +/- gentamicin for four (native valve) to six weeks (prosthetic valve). A third-generation cephalosporin OR aztreonam are reasonable alternatives if resistance OR allergies preclude the use of beta-lactams.
Notes
Increasing resistance to tetracycline and sulfa precludes their use empirically.
Curious Cases
Relevant links to my Medscape blog
Last update: 01/30/20