Haemophilus infections

The incidence of mixed viral⁄bacterial infections has increased recently because of the dramatic increase in antibiotic-resistant strains, the emer-gence of new pathogens, and the resurgence of old ones. Despite the relat-ively well-known role of viruses in enhancing bacterial infections, the impact of bacterial infections on viral infections remains unknown.

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Antibiotic Regimens Otitis Media (Table 128-4) Current treatment recommendations for otitis media are based on the following points: (1) Acute otitis media is the most common diagnosis leading to an antibiotic prescription in the United States. (2) The diagnosis is often based on inadequate evidence for true middle-ear infection. (3) In proven cases, S. pneumoniae and H. influenzae are the most likely causes.

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Site of Infection The location of the infected site may play a major role in the choice and dose of antimicrobial drug. Patients with suspected meningitis should receive drugs that can cross the blood-CSF barrier; in addition, because of the relative paucity of phagocytes and opsonins at the site of infection, the agents should be bactericidal. Chloramphenicol, an older drug but occasionally useful in the treatment of meningitis, is bactericidal for common organisms causing meningitis (i.e.

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Clinical Manifestations Infection is acquired as the result of a break in the epithelium during sexual contact with an infected individual. After an incubation period of 4–7 days, the initial lesion—a papule with surrounding erythema—appears. In 2 or 3 days, the papule evolves into a pustule, which spontaneously ruptures and forms a sharply circumscribed ulcer that is generally not indurated (Fig. 139-2). The ulcers are painful and bleed easily; little or no inflammation of the surrounding skin is evident.

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Harrison's Internal Medicine Chapter 140. Infections Due to the HACEK Group and Miscellaneous Gram-Negative Bacteria The HACEK Group HACEK organisms are a group of fastidious, slow-growing, gram-negative bacteria whose growth requires an atmosphere of carbon dioxide. Species belonging to this group include several Haemophilus species, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella kingae. HACEK bacteria normally reside in the oral cavity and have been associated with local infections in the mouth.

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Prevention Vaccination (See also Chap. 116) The development of conjugate vaccines that prevent invasive infections with Hib in infants and children has been a dramatic success. Three such vaccines are licensed in the United States. In addition to eliciting protective antibody, these vaccines prevent disease by reducing rates of pharyngeal colonization with Hib. The widespread use of conjugate vaccines has dramatically reduced the incidence of Hib disease in developed countries. Even though the manufacture of Hib vaccines is costly, vaccination is cost-effective.

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Harrison's Internal Medicine Chapter 139. Haemophilus Infections Haemophilus influenzae Microbiology Haemophilus influenzae was first recognized in 1892 by Pfeiffer, who erroneously concluded that the bacterium was the cause of influenza. The bacterium is a small (1- by 0.3-µm) gram-negative organism of variable shape; hence, it is often described as a pleomorphic coccobacillus. In clinical specimens such as cerebrospinal fluid (CSF) and sputum, it frequently stains only faintly with phenosafranin and therefore can easily be overlooked. H.

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Pathogenesis Hib strains cause systemic disease by invasion and hematogenous spread from the respiratory tract to distant sites such as the meninges, bones, and joints. The type b polysaccharide capsule is an important virulence factor affecting the bacterium's ability to avoid opsonization and cause systemic disease. Nontypable strains cause disease by local invasion of mucosal surfaces. Otitis media results when bacteria reach the middle ear by way of the eustachian tube. Adults with chronic bronchitis experience recurrent lower respiratory tract infection due to nontypable strains.

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Nontypable H. influenzae Nontypable H. influenzae is a common cause of community-acquired bacterial pneumonia in adults. Nontypable H. influenzae pneumonia is especially common among patients with COPD or AIDS. The clinical features of H. influenzae pneumonia are similar to those of other types of bacterial pneumonia (including pneumococcal pneumonia). Patients present with fever, cough, and purulent sputum, usually of several days' duration. Chest radiography reveals alveolar infiltrates in a patchy or lobar distribution.

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