Invasive disease due to nontypable Haemophilus influenzae in children.

Its virulence factors, immune responses, and sites of isolation characterize nontypable Haemophilus influenzae as a pathogen of mucosal surfaces which rarely causes invasive disease. We isolated nontypable H influenzae in pure culture from thoracentesis fluid in a child with pneumonia. An extensive review of the literature in which serotyping of H influenzae was reported revealed that nontypable strains have accounted for only six other cases of pneumonia diagnosed by blood culture, lung puncture, or thoracentesis fluid. The only isolate reported to cause disease outside the neonatal age group may have been a typable strain. Because this organism rarely causes invasive disease, its isolation from sputum is of questionable significance and other causes should be sought.