Bacteriology and clinical significance of hemolytic Haemophilus in the throat.

Hemolytic Haemophilus are rarely isolated in the clinical laboratory, as they do not grow on sheep or human blood-agar alone. On rabbit blood-agar they grow well and are hemolytic, but they grow less well and are not hemolytic on sheep blood-agar with added X and V factors. A survey was made to determine their incidence in pharyngitis. From 28 of 100 sore throats and from 57 of 100 normal throats, only normal bacterial flora were isolated. beta-Streptococci were present in significant numbers in 9 sore and 11 normal throats; staphylococci in 8 sore and 4 normal throats; pneumococci in 20 sore and 11 normal throats; H. influenzae or H. parainfluenzae in 13 sore and no normal throats; hemolytic Haemophilus in 30 sore and 18 normal throats; enteric bacilli in 1 of each; Candida and Neisseria in 2 sore throats each. All of the 33 hemolytic Haemophilus isolates identified to species were H. parahaemolyticus. All were sensitive in vitro to chloramphenicol, erythromycin, and tetracycline; 30 were sensitive to ampicillin and 30 to penicillin, 26 to novobiocin, and 12 to methicillin. H. influenzae, H. parainfluenzae, and H. haemolyticus are indistinguishable by Gram stain morphology, but H. parahaemolyticus is larger than the other three. Hemolytic and nonhemolytic species are indistinguishable by colonial morphology or by nutritional requirements; only hemolysis gives positive differentiation. Nevertheless, only rarely would this be of clinical importance. H. parahaemolyticus apparently may cause pharyngitis, but it is almost always susceptible to penicillin and rarely if ever causes sequelae.