Tags: Diphtheria

Important Anaerobes

Anaerobic bacteria are the predominant component of the normal microbial flora of the human body. The following sites harbor the vast majority of them:

Haemophilus, Bordetella, & Branhamella Species

Before 1990, strains of Haemophilus influenzae type b were found in the upper respiratory tract of 3-5% of children and a small percentage of adults. Colonization rates with type-b strains are even lower now, reflecting routine immunization of infants against H influenzae type b. Non-type-b encapsulated H influenzae are present in the nasopharynx of < 2% of individuals, whereas nonencapsulated (nontypable [see below]) strains colonize the respiratory tract of 40-80% of children and adults.

Bordetella Species: Clinical Syndrome

The catarrhal stage is characterized by nonspecific upper respiratory symptoms, including rhinorrhea, mild cough, and low-grade fever. During this stage, which typically lasts 1-2 weeks, the disease is highly communicable. The paroxysmal stage is marked by sudden attacks or paroxysms of severe, repetitive coughing, often culminating with the characteristic whoop and frequently followed by vomiting.

Haemophilus Influenzae: Clinical Syndromes

H influenzae was first isolated during the 1892 influenza pandemic and was originally believed to be the causative agent of influenza. Although subsequent studies revealed the fallacy of this idea, H influenzae has proved to be a common cause of localized respiratory tract and systemic disease, including meningitis, epiglottitis, pneumonia, pyogenic arthritis, cellulitis, otitis media, and sinusitis, among others (Box 1). Meningitis is the most common and serious form of invasive H influenzae type-b disease. In the mid-1980s, before the introduction of effective vaccines, ~ 10,000-12,000 cases of H influenzae type-b meningitis occurred in the United States each year, and 95% of cases involved children < 5 years old.

Pseudomonas Aeruginosa

The genus Pseudomonas consists of a number of human pathogens, the most important of which is Pseudomonas aeruginosa. P aeruginosa is an opportunistic pathogen found widely in soil, water, and organic material, reflecting its limited nutritional requirements. A moist environment is favored. Human colonization in the community is rare, and, when it occurs, the skin, gut, and upper or lower airway are colonized.

Gram-Positive Aerobic Bacilli

L monocytogenes is found in soil, fertilizer, sewage, and stream water; on plants; and in the intestinal tracts of many mammals. It is a foodborne pathogen that causes bacteremic illness and meningoencephalitis, with few if any gastrointestinal manifestations.

Diphtheria

Humans are the only known natural hosts for C diphtheriae, the organism that causes diphtheria. This organism is usually spread via upper respiratory tract droplets, but it can also be spread by direct contact with skin lesions. Transmission appears to be more common when people are living indoors in crowded conditions.

Other Syndromes

Primary pneumococcal bacteremia (ie, no identifiable anatomic focus) is common in children but infrequent in adults. S pneumoniae is the major pathogen of otitis media in children, being responsible for between 33% and 50% of all cases in which an etiologic agent can be identified. It is also one of the two most important (along with H influenzae) agents implicated in acute sinusitis.

Parainfluenza Virus

Parainfluenza is a ubiquitous virus. It is the primary cause of acute laryngotracheobronchitis (croup) in children aged 6 months to 3 years. It is capable of infecting the lower respiratory tract as well by manifesting as bronchiolitis or pneumonia. Outbreaks can follow regular epidemic patterns or be sporadic. Certain antigenic types (described below) do follow epidemic patterns.