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).
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.
H. influenza type a can also cause invasive disease (PubMed) .
Invasive disease should result in a work-up for antibody deficiencies and other immunodeficiencies (PubMed).
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.
Increasing resistance to tetracycline and sulfa precludes their use empirically.