Pneumonia caused by Haemophilus influenzae bacteria, computer illustration. H. influenzae are coccobacillus Gram-negative bacteria. These bacteria cause a number of diseases including meningitis in children, pneumonia, epiglottitis, laryngitis, conjunctivitis, neonatal infection, otitis media (middle ear infection) and sinusitis in adults. H. influenzae harmlessly colonize the upper respiratory tract in most humans within the first few months of life. Encapsulated strains spread to cause diseases such as bronchitis and pneumonia.