Nontypable Haemophilus Influenzae Meningitis

Since 1988 when Haemophilus influenzae type b (Hib) conjugate vaccines were introduced, there has been a rapid and substantial decline in the incidence of invasive Hib disease in infants and children.1 Vaccination has also caused a decline in the pharyngeal colonization with Hib in this group.2 In light of these findings some investigators have suggested that a concurrent increase in disease caused by other capsular types or nontypable H. influenzae strains is to be anticipated.3, 4 We report a case of nontypable H. influenzae meningitis in a previously healthy 10-year-old boy and discuss a method of unequivocal organism identification by polymerase chain reaction. Case report. The patient, a 10-year-old white boy, was well until the day of admission, when he experienced the sudden onset of headache and nausea. On examination several hours later he had an oral temperature of 38.5°C and normal vital signs. He complained of severe headache but did not appear toxic. Nuchal rigidity was prominent but there was no photophobia. Examination of the head, eyes, ears, nose and throat was normal; skin was without rashes or petechiae; and the neurologic examination was normal. The remainder of the physical examination was unremarkable. Laboratory evaluation revealed a white blood cell count of 25 800/mm3 with 74% polymorphonuclear leukocytes, 11% band forms and 8% lymphocytes. The cerebrospinal fluid contained 1034 white blood cells/mm3 with 69% polymorphonuclear leukocytes and 31% lymphocytes, 1108 red blood cells/mm3, protein of 131 mg/dl and glucose of 41 mg/dl, with blood glucose of 183 mg/dl. The Gram-stained smear of the spinal fluid showed no bacteria. Cultures of blood were sterile. Culture of cerebrospinal fluid yielded beta-lactamase-producing nontypable H. influenzae. Treatment with intravenous ceftriaxone 50 mg/kg every 12 h was started and continued for 10 days, 4 days in the hospital and 6 days as an outpatient. The child responded well to therapy, with headache and meningismus markedly improved within 24 h. Fever resolved by the third hospital day. At discharge on Day 4 the physical examination was normal. Because the H. influenzae was nontypable an immunologic evaluation was initiated. The patient had an unremarkable past medical history and had received the appropriate childhood vaccinations, including a single dose of Hib vaccine at age 30 months. Quantitative serum immunoglobulins, total complement hemolytic activity and antibody titers to tetanus and diphtheria were normal. Serum antibody concentrations to five of six pneumococcal serotypes tested were also normal, reflecting normal response to prior exposure. Further characterization of the infecting organism was pursued. Biotyping was performed by defining reactions with indole, urease and ornithine decarboxylase, identifying H. influenzae biotype III. Organism identification and biotyping were confirmed by the Centers for Disease Control in Atlanta, GA. The H. influenzae isolate was then evaluated by PCR for serotype-specific capsular DNA and for a gene (bexA) obligatory for capsular export (experiments performed in the laboratory of M. M. Farley, Emory University School of Medicine). PCR was performed with primers HI-1 and HI-2 (specific for the bexA gene), b1 and b2 (type b capsule-specific primers) and f1 and f2 (type f capsule-specific primers), with appropriate positive and negative H. influenzae controls.5 No capsule-associated DNA was identified, confirming the classification as a nontypable strain. Discussion. Pittman6 originally described six antigenically distinct capsular types of H. influenzae, designated a to f, in 1931. Nontypable strains are distinguished from other isolates of H. influenzae by their absence of a polysaccharide capsule. They are identified on the basis of their failure to agglutinate with typing antisera directed against capsular types a through f. Nontypable isolates are genetically diverse and in general not capsule-deficient phenotypic variants of encapsulated strains.7 Noncapsulate spontaneous deletion mutants of H. influenzae type b (b- strains) have been described but their role in invasive disease remains unclear.8 In the 1970s Killian9 described the separation of H. influenzae isolates into eight subgroups called biotypes. Subsequent investigators have used a variety of techniques to classify isolates. At present the standard method of laboratory identification involves assigning capsular type by agglutination with serotype-specific antiserum. A potential confounding factor is that many nontypable strains autoagglutinate. Most recently PCR-based assays have been developed for rapid identification of capsule-specific DNA in H. influenzae, allowing unequivocal assignment of capsular type.5 The capsule-associated gene bexA, identified by Kroll8 in 1988, encodes an export protein necessary for polysaccharide capsule expression in H. influenzae. When bexA primers are used in conjunction with primers derived from capsule type-specific DNA sequences, capsulate, noncapsulate and capsule-deficient type b mutant (b-) strains can be differentiated. PCR capsular typing overcomes the problems of cross-reaction and autoagglutination associated with serotyping of H. influenzae strains. Nontypable strains of H. influenzae have been rarely reported as a cause of meningitis in infants and children.10 In the pre-Hib vaccine era little attention was paid to the identification of such strains, because the predominance of early childhood meningitis was caused by H. influenzae type b. In contrast approximately one-half of the cases of H. influenzae meningitis in adults are caused by nontypable strains. Most adults in whom nontypable H. influenzae meningitis develops have predisposing factors such as cerebrospinal fluid leaks, head trauma or immune compromise. With the elimination of the majority of childhood H. influenzae type b invasive disease, other serotypes and nontypable strains are becoming increasingly visible as pathogens. In particular capsular types e and f have been implicated. Urwin et al.4 have recently published data showing a trend toward increasing H. influenzae type f disease prevalence, although their data represent surveillance in adults as well as children. Bisgard et al.1 reviewed national surveillance data from 1994 and 1995 and found that non-type b encapsulated H. influenzae and nontypable strains represented 18 and 8%, respectively, of identified isolates in children <5 years of age who have H. influenzae meningitis. These organisms must be considered potential pathogens, even in anatomically and immunologically normal patients. Thorough investigation of all childhood H. influenzae meningitis, particularly cases occurring in vaccine recipients, is recommended. Sara L. Cuthill, M.D. Monica M. Farley, M.D. Leigh G. Donowitz, M.D.