Pneumonia and acute febrile tracheobronchitis due to haemophilus influenzae.

Of 30 patients with pneumonia due to Haemophilus influenzae, 26 had infection due to nontypable and 4 due to typable organisms. Biotype I isolates were implicated with surprising frequency. Blood cultures were positive in six patients. An additional 14 patients, all with nontypable H. influenzae infection, had febrile purulent tracheobronchitis that was clinically indistinguishable from pneumonia except for the absence of a radiographic infiltrate; none were bacteremic. Penicillin susceptibility was shown for 95% of isolates, and response to ampicillin was prompt. Patients had high serum levels of bactericidal antibody on admission but had lower levels of serum opsonizing activity against their own organism than did uninfected carriers with chronic bronchitis; 2 to 3 weeks later, levels of opsonizing antibody had risen to equal those of carriers. Deficient opsonizing activity may have contributed to susceptibility to infection. These findings identify both host and bacterial factors that may cause susceptibility to pulmonary infection from H. influenzae.