Haemophilus Influenzae Surveillance and Its Clinical Laboratory Diagnosis

Haemophilus influenzae is an aerobic pleomorphic gram-negative coccobacillus that requires both X and V factors for growth. It grows poorly, if at all, on ordinary blood agar unless streaked with Staph. aureus. It grows well on chocolate agar. Because this medium is often not used in culturing specimens from adults and because the organism may be overgrown by other bacteria, the frequency of H. influenzae infections has undoubtedly been seriously underestimated. This is aggravated by the failure of many physicians to obtain blood cultures in suspected bacterial infections and the failure of many laboratories to subculture them routinely onto chocolate agar. H. influenzae, along with Streptococcus pneumoniae, is a major factor in acute sinusitis. It is probably the most frequent etiologic agent of acute epiglottitis. It is probably a common, but commonly unrecognized, cause of bacterial pneumonia, where it has a distinctive appearance on Gram stain. It is unusual in adult meningitis, but should particularly be considered in alcoholics; in those with recent or remote head trauma, especially with cerebrospinal fluid rhinorrhea; in patients with splenectomies and those with primary or secondary hypogammaglobulinemia. It may rarely cause a wide variety of other infections in adults, including purulent pericarditis, endocarditis, septic arthritis, obstetrical and gynecologic infections, urinary and biliary tract infections, and cellulitis. Antimicrobial susceptibility testing is somewhat capricious in part from the marked effect of inoculum size in some circumstances. In vitro and in vivo results support the use of ampicillin, unless the organism produces beta- lactamase. Alternatives in minor infections include tetracycline, erythromycin, and sulfamethoxazole-trimethoprim. For serious infections chloramphenicol is the best choice if the organism is ampicillin-resistant or the patient is penicillin- allergic.