Haemophilus influenzae and haemophilus parainfluenzae in chronic obstructive pulmonary disease

The importance of nonencapsulated strains of Haemophilus influenzae and H. parainfluenzae in the pathogenesis of chronic obstructive pulmonary disease (C.O.P.D.) has been investigated in 150 patients observed at two-month intervals from 1968 to 1975. H. influenzae was distinguished from H. parainfluenzae by demonstrating requirements for both X and V factors. H. influenzae was isolated more often from sputum cultures from patients with severe C.O.P.D. (13.8%) than from patients with mild disease (4.4%, P less than 0.01). In contrast, H. parainfluenzae was isolated with equal frequency from sputums of patients with mild (40%) or severe (43%) disease. H. influenzae was present in the sputum more often during exacerbations of acute respiratory illness (15.4%) than during sympton-free periods (9.6%, P less than 0.01), while isolation rates of H. parainfluenzae did not increase during periods of illness (35% versus 39%). Antigens specific for the H. influenzae species and for the H. parainfluenzae species were used in a complement-fixation test to detect antibody rises in sera collected from the patient population. Fourfold or greater rises in titre of antibodies to H. influenzae were detected on 76 occasions in 53 patients, and 46 of these rises were associated with acute respiratory illnesses. In contrast, no antibody rises were detected with the H. parainfluenzae antigen. These observations indicate that nonencapsulated strains of H. influenzae may have pathogenic potential in patients with C.O.P.D., whilst H. parainfluenzae should be considered as normal flora.